Publications

abstract
Growth of structural mass and energy reserves influences individual survival, reproductive success, and population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue deposition for structural growth and energy stores and their prioritization within bioenergetic budgets are poorly documented. This is particularly true across marine mammal species as resources are accumulated at sea, limiting the ability to measure energy allocation and prioritization. We reviewed the literature on marine mammal growth to summarize growth patterns, explore their tissue compositions, assess the energetic costs of depositing these tissues, and explore the tradeoffs associated with growth. Generally, marine mammals exhibit logarithmic growth. This means that the energetic costs related to growth and tissue deposition are high for early postnatal animals, but small compared to the total energy budget as animals get older. Growth patterns can also change in response to resource availability, habitat, and other energy demands, such that they can serve as an indicator of individual and population health. Composition of tissues remained consistent with respect to protein and water content across species; however, there was a high degree of variability in the lipid content of both muscle (0.1-74.3%) and blubber (0.4-97.9%) due to the use of lipids as energy storage. We found that relatively few well-studied species dominate the literature, leaving data gaps for entire taxa, such as beaked whales. The purpose of this review was to identify such gaps, to inform future research priorities, and to improve our understanding of how marine mammals grow and the associated energetic costs.

keywords     growth, bioenergetics, body composition, northern fur seals

abstract
Sea otters (Enhydra lutris) are known ecosystem engineers that have significant impacts on their kelp forest and rocky intertidal communities due to their high levels of food intake. Quantifying sea otter food biomass and energy intake is a valuable way to understand potential ecological impacts of sea otter populations on ecosystems and for predicting future population trends and potential for expansion. While detailed, fine-scale, age-specific food intake is difficult to quantify in wild sea otters, there is a wealth of potential information available from otters under human care. This study used food and energy intake data from husbandry records of 10 sea otters collected over three decades at the Vancouver Aquarium. Within these husbandry records, daily food biomass intake and body mass measurements were recorded and converted to annual average food mass and gross energy intake (GEI). Age-, sex-, and mass-specific trends were also observed. Young sea otters had the highest relative ingested food mass, equivalent to ~26% of body mass, which decreased to ~20% in adult otters. Young otters similarly had the high- est mass-specific GEI, where measures from near birth to year 1 were ~40% higher than at year 3, the age of sexual and physical maturity. There were also key differences in trends between sexes. Captive adult male sea otters were 25 to 42% larger than females and their GEI was 23 to 58% higher, although mass-specific GEI was almost identical for male and non-reproductive female otters at all ages, plateauing at ~650 kJ kg-1 d-1. Despite high levels of ingested food mass, GEI was only 5 to 15% higher than for other captive marine mammals and was comparable to previous estimates for wild sea otters. These estimates of ingested food mass and energy intake requirements are valuable when modelling the ecological impact of sea otter populations and for considering the potential effects of future environmental changes.

keywords     sea otters, Enhydra lutris, food intake, energetics, nutrition, growth, body mass

abstract
Between 2012 and 2022, the Vancouver Aquarium Marine Mammal Rescue Centre sedated 110 harbor seal pups for physical examinations, diagnostic procedures, or treatment. A sedation protocol of butorphanol and midazolam (0.1– 0.2 mg/kg each) was administered via a single i.v. injection in 171 procedures. Of these, 21 pups were anesthetized only with the injectables, while supplemental isoflurane inhalation anesthesia by mask was provided during 58 procedures; 92 other animals required intubation for respiratory support due to apnea or to achieve a deeper plane of anesthesia to facilitate more invasive procedures. Of the 171 sedations, five were euthanized due to poor prognosis and six failed to recover. Maximum sedation, sufficient for intended procedure or anesthesia induction, was achieved within a mean of 8.5 ± 5.8 min for i.v. injection (n = 133). Sedation duration (drug administration to full recovery) without supplemental inhalation anesthesia had a mean of 30.2 min and ranged from 14 to 52 min (n = 13). When used in stabilized young harbor seals, administration of injectable butorphanol and midazolam proved to be an effective protocol to obtain safe and reliable sedation for physical examination, minimally invasive diagnostic procedures, or as a premedication for general anesthesia.

keywords     harbour seal, seadtion, marine mammal medicine, husbandry

abstract
Bioenergetics is the study of how animals achieve energetic balance. Energetic balance results from the energetic expenditure of an individual and the energy they extract from their environment. Ingested energy depends on several extrinsic (e.g prey species, nutritional value and composition, prey density and availability) and intrinsic factors (e.g. foraging effort, success at catching prey, digestive processes and associated energy losses, and digestive capacity). While the focus in bioenergetic modelling is often on the energetic costs an animal incurs, the robust estimation of an individual’s energy intake is equally critical for producing meaningful predictions. Here, we review the components and processes that affect energy intake from ingested gross energy to biologically useful net energy (NE). The current state of knowledge of each parameter is reviewed, shedding light on research gaps to advance this field. The review highlighted that the foraging behaviour of many marine mammals is relatively well studied via biologging tags, with estimates of success rate typically assumed for most species. However, actual prey capture success rates are often only assumed, although we note studies that provide approaches for its estimation using current techniques. A comprehensive collation of the nutritional content of marine mammal prey species revealed a robust foundation from which prey quality (comprising prey species, size and energy density) can be assessed, though data remain unavailable for many prey species. Empirical information on various energy losses following ingestion of prey was unbalanced among marine mammal species, with considerably more literature available for pinnipeds. An increased understanding and accurate estimate of each of the components that comprise a species NE intake are an integral part of bioenergetics. Such models provide a key tool to investigate the effects of disturbance on marine mammals at an individual and population level and to support effective conservation and management.

keywords     marine mammals, energy intake, bioenergetics

abstract
Biologging tags that record high-resolution tri-axial accelerometry data are proving to be integral to the study of foraging ecology of large, free-roaming marine mammals, such as whales. They have been applied to a number of baleen whale species that feed pelagically through lunges or ram filtration to quantitatively define behaviours and estimate energetic costs. However, few behavioural ecology studies using accelerometry data have been conducted on grey whales, a unique baleen whale that performs benthic suction feeding. Using suction cup tri-axial accelerometer tag deployments on 10 Pacific Coast Feeding Group (PCFG) grey whales along the Oregon and Washington coasts, I defined signals of foraging behaviour at both the broad state (dive) and foraging tactic (roll event) scales. I then estimated the relative energetic cost of these behaviours using energy expenditure proxies derived from the accelerometry data—Overall Dynamic Body Acceleration (ODBA; ms-2), stroke rate (Hz), stroke amplitude (radians per s), and duration of dives with different foraging tactics performed (min). Hidden Markov Models (HMMs) defined three biologically distinct states—forage, search, and transit—using turn angle, dive duration, dive tortuosity and presence of roll events. Classification and Regression Tree (CART) models best defined the foraging tactics of headstands, benthic digs, and side swims using median pitch, depth to body length ratio, and absolute value of the median roll. These definitions of grey whale foraging signals using accelerometry data add to the quantitative descriptions of foraging behaviours previously described for baleen whales. Stroke rate identified foraging and headstanding as being the most energetically costly activities at the broad state and foraging tactic scales. These findings contribute to the foundational understanding of grey whale foraging energetics needed to assess the impacts of various conservation concerns on the fitness and interpret patterns of behaviour choice of this unique group of grey whales.

abstract
Between 20 and 24 marine extinctions, ranging from algal to mammal species, have occurred over the past 500 years. These relatively low numbers question whether the sixth mass extinction that is underway on land is also occurring in the ocean. There is, however, increasing evidence of worldwide losses of marine populations that may foretell a wave of oncoming marine extinctions. A review of current methods being used to determine the loss of biodiversity from the world’s oceans reveals the need to develop and apply new assessment methodologies that incorporate standardized metrics that allow comparisons to be made among different regions and taxonomic groups, and between current extinctions and past mass extinction events. Such efforts will contribute to a better understanding of extinction risk facing marine flora and fauna, as well as the ways in which it can be mitigated.

keywords     Biodiversity loss; sixth mass extinction; overfishing; extirpation; extinction risk

abstract
Background: Animal movement data are regularly used to infer foraging behaviour and relationships to environmental characteristics, often to help identify critical habitat. To characterize foraging, movement models make a set of assumptions rooted in theory, for example, time spent foraging in an area increases with higher prey density. Methods: We assessed the validity of these assumptions by associating horizontal movement and diving of satellite‐ telemetered ringed seals (Pusa hispida)—an opportunistic predator—in Hudson Bay, Canada, to modelled prey data and environmental proxies. Results: Modelled prey biomass data performed better than their environmental proxies (e.g., sea surface temperature) for explaining seal movement; however movement was not related to foraging effort. Counter to theory, seals appeared to forage more in areas with relatively lower prey diversity and biomass, potentially due to reduced foraging efficiency in those areas. Conclusions: Our study highlights the need to validate movement analyses with prey data to effectively estimate the relationship between prey availability and foraging behaviour.

abstract
The ecological impact of environmental changes at high latitudes (e.g., increasing temperature, and decreased sea ice cover) on low-trophic species, such as bowhead whales, are poorly understood. Key to understanding the vulnerability of zooplanktivorous predators to climatic shifts in prey is knowing whether they can make behavioural or distributional adjustments to maintain sufficient prey acquisition rates. However, little is known about how foraging behaviour and associated environmental conditions fluctuate over space and time. We collected long-term movement (average satellite transmission days were 397 (±204 SD) in 2012 and 484 (±245 SD) in 2013) and dive behaviour data for 25 bowhead whales equipped with time-depth telemetry tags, and used hierarchical switching-state-space models to quantify their movements and behaviours (resident and transit). We examined trends in inferred two-dimensional foraging behaviours based on dive shape of Eastern Canada-West Greenland bowhead whales in relation to season and sea ice, as well as animal sex and age via size. We found no differences with regards to whale sex and size, but we did find evidence that subsurface foraging occurs year-round, with peak feeding occurring in fall (7.3 hrs d-1 ± 5.70 SD; October) and reduced feeding during spring (2.7 hrs d-1 ± 2.55 SD; May). Although sea ice cover is lowest during summer foraging, whales selected areas with 65% (± 36.1 SD) sea ice cover. During winter, bowheads occurred in areas with 90% (± 15.5 SD) ice cover, providing some open water for breathing. The depth of probable foraging varied across seasons with animals conducting epipelagic foraging dives (< 200 m) during spring and summer, and deeper mesopelagic dives (> 400 m) during fall and winter that approached the sea bottom, following the seasonal vertical migration of lipid-rich zooplankton. Our findings suggest that, compared to related species (e.g., right whales), bowheads feed at relatively low rates and over a large geographic area throughout the year. This suggests that bowhead whales have the potential to adjust their behaviours and shift their distributions to adapt to climate-change induced environmental conditions. However, the extent to which energetic consumption may vary seasonally is yet to be determined.

abstract
OBJECTIVE To establish normal values for pre- and post-prandial bile acids and protein C in Pacific harbor seal (Phoca vitulina richardsi) pups. ANIMALS 45 harbor seals undergoing rehabilitation at the Vancouver Aquarium Marine Mammal Rescue Centre, 0 to 16 weeks, and deemed healthy aside from malnutrition or maternal separation. PROCEDURES Venous blood was collected from the intervertebral extradural sinus in fasted seals and again 2 hours after a fish meal. RESULTS The reference interval (90% CL, confidence limit) for pre-prandial (fasting) bile acids was 17.2 μmol/L to 25.4 μmol/L, post-prandial bile acids were 36.9 μmol/L to 46.4 μmol/L, and protein C was 72.3% to 85.4%, across ages. For comparison between developmental ages, pups were grouped into 3 age classes: < 14 days, 5 to 8 weeks, and 10 to 16 weeks. Age affected pre- and post-prandial bile acids; pups < 14 days had significantly higher pre-prandial bile acids (36.0 μmol/L ± 16.5 μmol/L; P < .0001) than other age groups and pups 5 to 8 weeks had significantly higher post-prandial bile acids (50.4 μmol/L ± 21.9 μmol/L; P < .001). Protein C was also affected by age, with seals < 14 days having significantly lower values (mean, 51.8% ± 16.7%; P < .0001). CLINICAL RELEVANCE This study established normal reference intervals for bile acids in harbor seal pups and offered a preliminary investigation into protein C in pinnipeds. The bile acid values from 0- to 16-week-old seal pups were well above established normal ranges for domestic species, highlighting the utility of age- and species-specific reference ranges. The values presented here and the differences across age classes will aid clinicians in accurately diagnosing hepatobiliary disease in harbor seal pups.

keywords     harbor seal pups, health, bile acids, Protein C

abstract
Pinniped populations around the world increased rapidly after hunting and culling during the nineteenth and twentieth centuries ended. Some believe that pinnipeds are now preventing the recovery of certain fish populations, and that controlling pinniped population abundance using lethal measures such as harvesting or by non‐lethal means like contraception could recover fish populations. It is unclear, however, how effective and how long it would take for such methods of population control to bring numbers of pinnipeds down to target levels. We used sex‐ and age‐structured population models to estimate how quickly harbor seal (Phoca vitulina) abundance in British Columbia, Canada, could be reduced by 50%, through combinations of lethal removals and sterilization of adult females. Models were fit to seal abundance, demographic, and harvest data collected between 1879 and 2014. Simulation modeling suggests reliance on contraception exclusively is unlikely to reduce the current harbor seal population (numbering ~100,000) by 50% within 25 years, and would result in more variable outcomes, compared to lethal removals. Contraception could be combined with harvesting to maintain a target abundance of harbor seals (although captive studies with harbor seals are needed to confirm the efficacy of contraception). Our simulation modeling approach provides a useful framework to assess how non‐lethal measures could be integrated into policies that promote active population control of harbor seal numbers.

keywords     British Columbia, harbor seal, integrated population model, population control, sterilization

abstract
Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted seals (Phoca largha), one ringed seal (Pusa hispida) and one bearded seal (Erignathus barbatus) during and outside the molting period, while resting in water and when hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species, regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

keywords     Energetics, Thermoregulation, Molting physiology, Respirometry

abstract
Eastern North Pacific grey whales (Eschrichtius robustus) rely on energy reserves obtained on their northern feeding grounds to complete their annual 17,000 km round-trip migration between the Arctic and Mexico. However, estimates of how much food is required to complete the annual migration is limited to adult whales of average size, and is not readily available across all age classes of males and females. I constructed an age-structured bioenergetics model using detailed information on the grey whale life cycle and migration timings to predict the energy requirements of different cohorts of grey whales. Results show that nursing calves require 24–35 L of milk daily in their first 9 to 10 months. Once weaned, juveniles require ~345 kg day-1 of benthic invertebrates (4.5% of body weight), while the largest adult whales will need a minimum of ~870 kg day-1 (4.3% of body weight) during the ~5 month (154 days) summer foraging season in the Arctic. In contrast, pregnant individuals need 1,630–1,969 kg of prey day-1 (9.3–10.3% of body weight) during this same period to support foetal growth and store sufficient energy to produce milk once the calves are born in Mexico. Lactating whales returning to the Arctic with their calves will require 1,360–1,960 kg of prey day-1 (8.2–8.9% of body weight) over the next 4.5 months to continue producing milk. My results can be combined with measured densities of benthic prey in the Arctic to assess and anticipate the likelihood of climate change or conspecific competition causing starvation-related mortality of grey whales in the future. My age-structured bioenergetics model is simple and flexible enough to adapt to any migratory species of interest, including rare, endangered species that may otherwise be considered data deficient.

abstract
Guadalupe fur seals (Arctocephalus townsendi) have established a second colony in the Gulf of California on El Farallón de San Ignacio Island, along the mainland coast of Mexico. They appear to have been coming to this island since 2014, and numbered as many as 771 in 2020 (mostly juveniles). The discovery of this new haulout brings the total number of sites where this species is known to rest and breed to just four. Guadalupe fur seals remain vulnerable and may require additional protection in the southern Gulf of California to secure their future.

keywords     Guadalupe, fur seal, endangered, Mexico, El Farallón de San Ignacio Island, Gulf of California, haulout

abstract
Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting exercise to identify high-priority unanswered questions in marine mammal bioenergetics, with an emphasis on questions relevant to conservation and management. Electronic communication and a virtual workshop were used to solicit and collate potential research questions from the marine mammal bioenergetic community. From a final list of 39 questions, 11 were identified as key questions because they received votes from at least 50% of survey participants. Key questions included those related to energy intake (prey landscapes, exposure to human activities) and expenditure (field metabolic rate, exposure to human activities, lactation, time-activity budgets), energy allocation priorities, metrics of body condition and relationships with survival and reproductive success, and extrapolation of data from one species to another. Existing tools to address key questions include labeled water, animal-borne sensors, mark-resight data from long-term research programs, environmental DNA, and unmanned vehicles. Further validation of existing approaches and development of new methodologies are needed to comprehensively address some key questions, particularly for cetaceans. The identification of these key questions can provide a guiding framework to set research priorities, which ultimately may yield more accurate information to inform policies and better conserve marine mammal populations.

abstract
Estimates of prey and energy consumption are important for effective management and conservation of marine mammals and the ecosystems they inhabit. We used routinely collected husbandry data on body mass, food intake (kilo- grams), and energy intake (megajoules) from northern fur seals (Callorhinus ursinus) in zoological institutions to examine how these variables changed throughout the year, and with age, sex, and reproduction. Fur seals exhibited seasonal changes in all three variables, but the magnitude and timing of trends varied among age and sex groups. Notably, adult males exhibited rapid increases in body mass leading up to the breeding season. Fur seals were most efficient at converting energy intake to mass gain in the spring and least efficient in the fall. Intake increased into adulthood as animals grew in body mass. Sex-specific differences in intake were detectable early in development, likely related to size dimorphism. Pregnancy was energetically inexpensive compared with lactation, with food and energy intake rapidly increasing post parturition to values that were double those during early pregnancy. This study highlights the importance of accounting for different age, sex, and life history stages when estimating prey consumption of northern fur seals.

keywords     bioenergetic model, caloric intake, energetics, fatted male phenomenon, growth, lactation, otariids

abstract
The global population of California sea lions (Zalophus californianus) has declined in the Gulf of California (Mexico), while numbers have increased along the California coastline (U.S.). It is unclear what is behind the divergent population trends, but differences in diets likely play a role. I used diet data to investigate whether the changes in sea lion population numbers that occurred in sea lion numbers from 1980–2020 could be explained by differences or shifts in diet quality — specifically energy density and diet diversity. I also explored whether diet quality in the Gulf of California was affected by increased sea surface temperatures that occurred in 2014. I considered rookeries in California (Channel Islands) to be a single ecological Zone and divided the Gulf of California breeding islands into nine Zones based on geographic proximities and similarities in population trajectories. Years with matching population and diet data within all these Zones were used to test for relationships between measures of diet quality and population changes. My results showed that diet variability and composition differed between the Channel Islands and the Zones within the Gulf of California. In general, sea lions breeding in the Gulf of California consumed a large variety of mostly benthic species and schooling fish, whereas sea lions at the Channel Islands primarily consumed schooling fish and squid. Contrary to expectations, no significant relationships were found between population changes and measures of diet quality across all Zones and times. However, the average energy density of sea lion diets in certain Zones within the Gulf of California declined as sea surface temperatures increased. While my results did not reveal a direct relationship between population changes and diet quality, they demonstrate the significance of considering the influence of environmental heterogeneity on regional population dynamics. My results also highlight the importance of better understanding the ecosystem dynamics of the Gulf of California at small regional scales. Such findings may be key to fully understanding the interplay between environmental changes, diets, and future population trajectories of California sea lions and other pinniped species in geographic locations throughout Mexico and the U.S.

abstract
Data sets comprised of sequences of curves sampled at high frequencies in time are increasingly common in practice, but they can exhibit complicated dependence structures that cannot be modelled using common methods of Functional Data Analysis (FDA). We detail a hierarchical approach which treats the curves as observations from a hidden Markov model (HMM). The distribution of each curve is then defined by another fine-scale model which may involve auto-regression and require data transformations using moving-window summary statistics or Fourier analysis. This approach is broadly applicable to sequences of curves exhibiting intricate dependence structures. As a case study, we use this framework to model the fine-scale kinematic movement of a northern resident killer whale (Orcinus orca) off the western coast of Canada. Through simulations, we show that our model produces more interpretable state estimation and more accurate parameter estimates compared to existing methods.

keywords     Accelerometer data; animal movement; biologging; diving behaviour; hierarchical modelling; killer whales; state-switching; statistical ecology; time series

abstract
Marine trophic ecology data are in high demand as natural resource agencies increasingly adopt ecosystem-based management strategies that account for complex species interactions. Harbour seal (Phoca vitulina) diet data are of particular interest because the species is an abundant predator in the northeast Pacific Ocean and Salish Sea ecosystem that consumes Pacific salmon (Oncorhynchus spp.). A multi-agency effort was therefore undertaken to produce harbour seal diet data on an ecosystem scale using, 1) a standardized set of scat collection and analysis methods, and 2) a newly developed DNA metabarcoding diet analysis technique designed to identify prey species and quantify their relative proportions in seal diets. The DNA-based dataset described herein contains records from 4,625 harbour seal scats representing 52 haulout sites, 7 years, 12 calendar months, and a total of 11,641 prey identifications. Prey morphological hard parts analyses were conducted alongside, resulting in corresponding hard parts data for 92% of the scat DNA samples. A custom-built prey DNA sequence database containing 201 species (192 fishes, 9 cephalopods) is also provided.

keywords     Marine, trophic ecology, data, harbor seal, Phoca vitulina, diet, Pacific Ocean, Salish Sea DNA metabarcoding, DNA proportions, scats, salmon, hake, herring

abstract
Five ecotypes of killer whales occur in the southern hemisphere: Types A, B (B1 and B2), C, and D. Antarctic Type A has a circumpolar distribution around Antarctica, and are often associated with their preferred prey (minke whales, seals and penguins) in ice-free waters. Ecotype B typically occurs near or within pack ice where they predomi­nantly consume seals, as well as fish, squid, and penguins. Type C killer whales have been predominantly sighted in East Antarctica, and relatively little is known about the Type D individuals. We report seven sightings of Antarctic Type B and C killer whales in Australian coastal waters—as well as a third morphological form, closely resembling the Antarctic Type A ecotype. These records confirm that at least two of the five Antarctic eco-types described from the Southern Hemisphere also occur in Australian coastal waters.

abstract
Knowing size‐at‐age is important for determining food requirements and making inferences about the nutritional status of individuals and their populations. Accurate growth curves are also needed to quantify drug dosages to treat wounded or entangled animals. However, body sizes are often based on small numbers of measured animals that must be improved as new data become available. We updated an existing body growth model for North Atlantic right whales (NARWs) using new data from dead animals and from older individuals. Our models indicate that NARWs attain mean lengths and weights of 4.3 m and 1.0 mt at birth, and 13.1 m and 31.7 mt when sexually mature. Calves more than double their length and attain nearly three‐quarters of their asymptotic adult size during their first year of life. Overall, our length estimates agreed well with previous estimates, but our mass‐at‐age values were considerably higher. These differences revealed that necropsy data used alone in allometric models underestimate mass due possibly to several of the stranded animals in the database having been chronically entangled and in poor body condition. Augmenting the database with healthier individuals, such as harvested North Pacific right whales, yielded mass predictions that reflect both healthy and unhealthy individuals.

keywords     body size, Eubalaena glacialis, growth models, length, mass, morphometry, photogrammetry

abstract
North Atlantic right whale (Eubalaena glacialis) population fed in the Gulf of St. Lawrence (Canada) in recent years. However, little is known about the distribution of copepods in the Gulf, and whether their abundance is sufficient to energetically sustain right whales. We used a mechanistic modeling approach to predict areas within the Gulf that have foraging potential for adult female right whales, based on the annual energetic needs of resting, pregnant, and lactating females, and their theoretical prey density requirements. We identified suitable foraging areas for right whales by coupling a foraging bioenergetics model with a 12-year data set (2006-2017) describing the abundance and three-dimensional distribution of late-stage Calanus spp. in the Gulf. Prey densities in the southern Gulf (from Shediac Valley to the Magdalen Islands) supported all three reproductive states in most (≥ 6) years. However, foraging habitat became progressively sparse in the southern Gulf over time, with noticeably less suitable habitat available after 2014. Few other potentially suitable foraging areas were identified elsewhere in the Gulf. Overall, the availability of foraging habitat in the Gulf varied considerably between years, and was higher for resting females than for pregnant and lactating females. Our findings are consistent with the recent low calving rates, and indicate that prey biomass in the Gulf of St. Lawrence may be insufficient in most years to support successful reproduction of North Atlantic right whales.

keywords     nutritional stress, bioenergetics, endangered, copepods, energy requirements, foraging, habitat, Calanus, right whale, Gulf of St Lawrence, prey density

abstract
Photo-identification studies of transient killer whales (Orcinus orcas) off western North America have primarily been conducted in the coastal inland waterways of Washington State, British Columbia, and southeastern Alaska. Less is known about transient killer whales along the outer coast and offshore waters of Oregon and central and northern California. We examined 13 years of photo-identification data to identify individuals and obtain a minimum census for this region, and to summarize information that could be useful for evaluating a hypothesis that whales using this area belong to a distinct assemblage. Data contributions came from opportunistic marine mammal surveys, whale watch ecotours, and dedicated line transect surveys. Transient killer whale photographs were obtained from 146 encounters between 2006 – 2018. These included 136 encounters in Monterey Bay, California, 5 encounters off central and northern California, and 5 encounters off Oregon. The number of unique individuals seen during this time totaled 155, of which 150 were considered to be alive (as of 2018). These included 34 adult males, 51 adult females, 24 sub-adults, and 41 juveniles. Through repeated observations of association patterns, a total of 30 matrilineal groups were identified. New whales were identified each year, including previously unidentified adults and new calves. Identification images of the dorsal fins, saddle patches and postocular patches were obtained. Details on sex, maternal ancestry, sighting history, and distribution are provided where known. These cataloged transient killer whales were predominantly encountered off the outer coast near the continental shelf break or in deep pelagic waters overlying the Monterey Submarine Canyon. The vast majority (>83 %) of whales identified in the study area could not be matched to transient killer whales in photo ID catalogs for coastal waters of the Pacific Northwest. These factors are consistent with there being a distinct “outer coast” assemblage within the west coast population of transient killer whales, but more research is needed to investigate this further.

abstract
Changes in Arctic ice conditions have raised concerns regarding potential impacts on energy expenditure and food requirements of walruses. Modelling the repercussions of environmental changes requires accurate species-specific measures of bioenergetic expenditures. This is particularly true for walruses, who have a unique anatomy and foraging ecology from other pinnipeds. This study measured resting metabolic rate (RMR) and subsurface swimming metabolism in two juvenile walruses over a 13-month period. The walruses had relatively low RMR compared to studies of other young pinnipeds. RMR was greater for the male than the female, as expected given his larger size; the reverse was true on a mass-specific basis. There was also considerable variability in RMR for each walrus during the year that could not be accounted for by changes in body mass. Metabolism while swimming was about twice RMR, and locomotor costs were higher than generally predicted for other marine mammals. The lower calculated swimming efficiency may reflect the fact that walruses are not “high velocity” pursuit predators. The estimates of metabolic expenditure obtained in this study for young walruses are invaluable for quantifying the energetic consequences of behavioral changes induced by environmental shifts in the wild.

keywords     bioenergetics, metabolism, swimming, walrus

abstract
This study quantified the effect of changes in prey intake on the growth of individual Steller sea lions. Data from 12 female sea lions subject to various experimental episodes of restricted food intake were used to produce an overall model predicting changes in growth rates from different levels of unpredicted reductions in energy intake. The resulting equation was robust across different types and levels of restriction, seasons, and age classes. This predictive relationship between changes in food intake and growth is invaluable for incorporating into bioenergetic models estimating the effects of environmental changes on wild Steller sea lions.

keywords     Steller sea lion, food intake, growth, body mass, energy intake, bioenergetics

abstract
Quantifying the energy needs of individual animals and understanding the relationship between food intake and physical growth are necessary to determine species-level food requirements and model potential responses to changing environmental conditions. To provide fine-scale information about developmental and seasonal patterns in the energetic requirements of Arctic phocid seals, we documented longitudinal changes in food intake, body mass, and standard length in four spotted seals (Phoca largha), three ringed seals (Pusa hispida), and two bearded seals (Erignathus barbatus). The seals were studied for up to 9 years in sub-Arctic and/or temperate climates while living under human care. Seals were fed using behavioral criteria that allowed their food intake and body mass to vary naturally. Gross energy intake (GEI) increased with age in all species, reaching a plateau as seals matured. GEI was greatest for the largest species (bearded seals) and lowest for the smallest (ringed seals). Mass-specific GEI declined with age, and was similar between spotted and ringed seals, with bearded seals consuming about half that of the smaller species. Overlaid upon long-term developmental changes were predictable seasonal cycles in food intake and body mass which became more pronounced as seals matured. Seasonal cycles in food intake and body mass did not always reflect simple cause-and-effect relationships. For example, seasonal peaks in food intake were regularly associated with simultaneous declines in body mass. The consistency of energy intake patterns, despite seals being maintained in semi-artificial conditions in different local climates, supports the hypothesis that seasonal oscillations are guided by underlying hormonal changes linked to key life history events and mediated by the physical environment. The described physiological patterns serve to highlight times of year when free-ranging Arctic seals may be more sensitive to environmental perturbations.

keywords     Phoca largha, Pusa hispida, Erignathus barbatus, food intake, caloric intake, body mass, growth, development, environmental conditions, nutrition

abstract
The decline of southern resident killer whales may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4-6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success.

abstract
An array of predators that consume juvenile salmon may account for the poor returns of adult salmon to the Salish Sea. However, the Pacific great blue heron (Ardea herodias fannini) is rarely listed among the known salmon predators, despite being regularly seen near salmon streams. Investigating heron predation by scanning nesting sites within 35 km of three British Columbia rivers for fecal remains containing Passive Integrated Transponder (PIT) tags implanted in >100,000 juvenile salmon from 2008-2018 yielded 1,205 tags, representing a minimum annual predation rate of 0.3-1.3% of all juvenile salmon. Most of this predation (99%) was caused by ~420 adult herons from three heronries. Correcting for tags defecated outside of the heronry raised the predation rates to 0.7-3.2%-and was as high as 6% during a year of low river flow. Predation occurs during chick-rearing in late spring, and accounts for 4.1-8.4% of the heron chick diet. Smaller salmon smolts were significantly more susceptible to heron predation than larger conspecifics. The proximity of heronries relative to salmon bearing rivers is likely a good predictor of heron predation on local salmon runs, and can be monitored to assess coast-wide effects of great blue herons on salmon recovery.

keywords     predation, salmon, smolts, herons, chicks, diet

abstract
Pinniped hearts have been well described via dissection, but in vivo measurements of cardiac structure, function, and electrophysiology are lacking. Electrocardiograms (ECGs) were recorded under anesthesia from 8 Steller sea lions (Eumetopias jubatus), 5 northern fur seals (Callorhinus ursinus), and 1 walrus (Odobenus rosmarus) to investigate cardiac electrophysiology in pinnipeds. In addition, echocardiograms were performed on all 8 anesthetized Steller sea lions to evaluate in vivo cardiac structure and function. Measured and calculated ECG parameters included P‑wave, PQ, QRS, and QT interval durations, P‑, R‑, and T‑wave amplitudes, P‑ and T‑wave polarities, and the mean electrical axis (MEA). Measured and calculated echocardiographic parameters included left ventricular internal diameter, interventricular septum thickness, and left ventricular posterior wall thickness in systole and diastole (using M-mode), left atrium and aortic root dimensions (using 2D), and maximum aortic and pulmonary flow velocities (using pulsed wave spectral Doppler). ECG measurements were similar to those reported for other pinniped species, but there was considerable variation in the MEAs of Steller sea lions and northern fur seals. Echocardiographic measurements were similar to those reported for southern sea lions (Otaria flavenscens), including 5 out of 8 Steller sea lions having a left atrial to aortic root ratio < 1, which may indicate that they have an enlarged aortic root compared to awake terrestrial mammals. Isoflurane anesthesia likely affected some of the measurements as evidenced by the reduced fractional shortening found in Steller sea lions compared to awake terrestrial mammals. The values reported are useful reference points for assessing cardiac health in pinnipeds under human care.

abstract
Although the ability of marine mammals to lower heart rates for extended periods when diving is well documented, it is unclear whether marine mammals have electrophysiological adaptations that extend beyond overall bradycardia. We analyzed electrocardiographic data from 50 species of terrestrial mammals and 19 species of marine mammals to determine whether the electrical activity of the heart differs between these two groups of mammals. We also tested whether physiological state (i.e., anesthetized or conscious) affects electrocardiogram (ECG) parameters. Analyses of ECG waveform morphology (heart rate, P-wave duration, and PQ, PR, QRS, and QT intervals) revealed allometric relationships between body mass and all ECG intervals (as well as heart rate) for both groups of mammals and specific differences in ECG parameters between marine mammals and their terrestrial counterparts. Model outputs indicated that marine mammals had 19% longer P-waves, 24% longer QRS intervals, and 21% shorter QT intervals. In other words, marine mammals had slower atrial and ventricular depolarization, and faster ventricular repolarization than terrestrial mammals. Heart rates and PR intervals were not significantly different between marine and terrestrial mammals, and physiological state did not significantly affect any ECG parameter. On average, ECG interval durations of marine and terrestrial mammals scaled with body mass to the power of 0.21 (range: 0.19 - 0.23) rather than the expected 0.25—while heart rate scaled with body mass to the power of -0.22 and was greater than the widely accepted -0.25 derived from fractal geometry. Our findings show clear differences between the hearts of terrestrial and marine mammals in terms of cardiac timing that extend beyond diving bradycardia. They also highlight the importance of considering special adaptations (such as breath-hold diving) when analyzing allometric relationships.

keywords     ECG, electrocardiogram, marine mammal, heart rate, anesthesia, allometry, cardiac timing, comparative electrophysiology

abstract
Arctic seals, including spotted (Phoca largha), ringed (Pusa hispida), and bearded (Erignathus barbatus) seals, are directly affected by sea ice loss. These species use sea ice as a haul-out substrate for various critical functions, including their annual molt. Continued environmental warming will inevitably alter the routine behavior and overall energy budgets of Arctic seals, but it is difficult to quantify these impacts as their metabolic requirements are not well known—due in part to the difficulty of studying wild individuals. Thus, data pertaining to species-specific energy demands is urgently needed to better understand the physiological consequences of rapid environmental change. We used open-flow respirometry over a four-year period to track fine-scale, longitudinal changes in the resting metabolic rate (RMR) of four spotted, three ringed, and one bearded seal trained to participate in research. Simultaneously, we collected complementary physiological and environmental data. Species-specific metabolic demands followed expected patterns based on body size, with the largest species, the bearded seal, exhibiting the highest absolute RMR (0.48±0.04 L O2 min-1) and the lowest mass-specific RMR (4.10±0.47 ml O2 min-1 kg-1), followed by spotted (absolute: 0.33±0.07 L O2 min-1; mass-specific: 6.13±0.73 ml O2 min-1 kg-1) and ringed (absolute: 0.20±0.04 L O2 min-1; mass-specific: 7.01±1.38 ml O2 min-1 kg-1) seals. Further, we observed clear and consistent annual patterns in RMR that related to the distinct molting strategies of each species. For species that molted over relatively short intervals—spotted (33±4 days) and ringed (28±6 days) seals—metabolic demands increased markedly in association with molt. In contrast, the bearded seal exhibited a prolonged molting strategy (119±2 days), which appeared to limit the overall cost of molting as indicated by a relatively stable annual RMR. These findings highlight energetic trade-offs associated with different molting strategies and provide quantitative data that can be used to assess species-specific vulnerabilities to changing conditions.

keywords     Arctic seals, spotted seal, ringed seal, bearded seal, sea ice, molt, climate change, respirometry, resting metabolic rate, energetic trade-offs

abstract
Two competing hypotheses were proposed to explain why Steller sea lions had declined in the Gulf of Alaska, Bering Sea and Aleutian Islands. One of the theories was that young sea lions were starving because fisheries had reduced the abundance of groundfish-the overfishing hypothesis. The other was that these low-fat species of fish had increased in abundance as the sea lion population declined following the 1976-1977 oceanic regime shift, and were compromising sea lion reproductive and survival rates-the junk-food hypothesis. Behavioral ecologists tested these hypotheses by comparing sea lion behaviors in the declining region (Gulf of Alaska and Aleutian Islands) with sea lion behaviors in an increasing region (Southeast Alaska) to determine whether the populations exhibited behavioral differences consistent with food shortages. These studies involved comparing dive depths, dive durations, time spent foraging, and time spent nursing by regions and seasons. Research also focused on weaning-a critical life-history stage-to determine when and how it occurs. Collectively, these observations and measures of behavioral responses revealed that most dependent young begin supplementing their milk diet with fish between April and May, and wean just before the start of the upcoming June breeding season. However, the proportion of young sea lions that wean at 1, 2 or 3 years of age appears to vary by year due to regional and temporal differences in the quantity and quality of prey available to them once weaned. None of the behavioral studies of adult and juvenile Steller sea lions supported the overfishing hypothesis-but were, instead, consistent with the junk-food hypothesis. It appears that lactating females that consume large amounts of low-energy fish (such as walleye pollock and Pacific cod) have a high probability of miscarriage, and will keep their dependent young for an extra one or two years-thereby causing birth rates and population size to decline. In contrast, lactating females that consume larger amounts of fattier fish (such as sand lance and Pacific herring) can successfully wean a pup every year. Plasticity in age at weaning appears to be an evolutionary adaptation to natural shifts in community prey structure in the North Pacific Ocean-and is an adaptation that successfully slows population declines of Steller sea lions until the ocean shifts to an alternative state containing greater portions of energy-rich fish that allows sea lion numbers to increase again.

keywords     Eumetopias jubatus, Life history, Population decline,Endangered, Maternal strategies, Phenology,Weaning, Abortions, Breeding, Junk food, Overfishing,Regime shifts

abstract
Availability of preferred salmonid prey and a sufficiently quiet acoustic environment in which to forage are critical to the survival of resident killer whales (Orcinus orcas) in the northeastern Pacific. Although piscivorous killer whales rely on echolocation to locate and track prey, the relationship between echolocation, movement, and prey capture during foraging by wild individuals is poorly understood. We used acoustic biologging tags to relate echolocation behavior to prey pursuit and capture during successful feeding dives by fish-eating killer whales in coastal British Columbia, Canada. The significantly higher incidence and rate of echolocation prior to fish captures compared to afterward confirms its importance in prey detection and tracking. Extremely rapid click sequences (buzzes) were produced before or concurrent with captures of salmon at depths typically exceeding 50 m, and were likely used by killer whales for close-range prey targeting, as in other odontocetes. Distinctive crunching and tearing sounds indicative of prey-handling behavior occurred at relatively shallow depths following fish captures, matching concurrent observations that whales surfaced with fish prior to consumption and often shared prey. Buzzes and prey-handling sounds are potentially useful acoustic signals for estimating foraging efficiency and determining if resident killer whales are meeting their energetic requirements.

keywords     biologging tag, echolocation, foraging behavior, killer whale, Orcinus orca, prey handling, salmon predation

abstract
Understanding variability in growth patterns of marine mammals provides insights into the health of individuals and status of populations. Body growth of gray whales (Eschrichtius robustus) has been described for particular life stages, but has not been quantified across all ages. We derived a comprehensive growth equation for gray whales by fitting a two-phased growth model to age-specific length data of eastern North Pacific gray whales that were captured, stranded, or harvested between 1926 and 1997. To predict mass-at-age, we used the allometric relationship between mass and length. We found that on average (± SD), calves were 4.6 ± 0.094 m and 972 ± 27 kg at birth, and reached 8.53 ± 0.098 m and 7,645 ± 162 kg by the end of their first year of life (n = 118). Thus, calves almost double (2×) in length and octuple (8×) in mass while nursing, and are effectively about two-thirds of their asymptotic adult length and one-third of their maximum mass when weaned. The large sample of aged individuals (n = 730) indicates that gray whales live up to ~48 years and have a life expectancy of < 30 years. Adult females attain a mean (± SD) asymptotic size of 13.2 ± 0.054 m and 20,706 ± 249 kg, while the smaller males average 12.6 ± 0.054 m and 19,812 ± 249 kg at ~40 years of age. Females are thereby ~4% longer and heavier than males. These age-specific estimates of body size can be used to estimate food requirements and assess nutritional status of individuals.

keywords     eastern gray whale, growth curves, length, life expectancy, longevity, mass, morphometrics, Putter model, sexual dimorphism

abstract
There is increasing evidence that predation by harbour seals on out-migrating salmon smolts may be responsible for the low return of adult coho and Chinook salmon in the Salish Sea. However, little attention has been given to understanding where and when this predation occurs, and the extent to which it might be conducted by few or many seals in the population. We equipped 17 harbour seals with data-loggers to track seal movements, and used accelerometry to infer prey encounter events (PEE) following the release of ~384,000 coho (May 4th) and ~3 million Chinook smolts (May 14th) into the Big Qualicum River. We found a small proportion (5.7%) of all PEE occurred in the estuary where salmon smolts entered the ocean-and that only one-quarter of the seals actively fed there. PEE counts increased in the estuary after both species of smolts were released. However, the response of the seals was less synchronous and occurred over a greater range of depths following the release of the smaller-bodied and more abundant Chinook smolts. Harbour seals feeding in the estuary appeared to target coho smolts at the beginning of May, but appeared to pursue predators of Chinook smolts in mid-May. PEE counts in the estuary increased as tide height rose, and were higher at dusk and night-especially during full moonlight. Such fine-scale behavioural information about harbour seals in relation to pulses of out-migrating smolts can be used to design mitigation strategies to reduce predation pressure by seals on salmon populations.

keywords     predation, salmon, harbour seals, coho, Chinook, data-loggers, biologging, accelerometry, accelerometers, prey encounters, estuary, size selection, mitigation, PIT tags

abstract
Pinnipeds have specific macronutrient (protein, lipid) requirements to satisfy physiological functions, yet little is known about how diet characteristics affect macronutrient digestibility. We measured relative and absolute lipid and protein digestibility in six female northern fur seals (Callorhinus ursinus (Linnaeus 1758)) fed eight experimental diets composed variously of four prey species (Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes 1847), walleye pollock (Gadus chalcogrammus Pallas 1814, formerly Theragra chalcogrammus (Pallas 1814)), capelin (Mallotus villosus (Müller 1776) and magister armhook squid (Berryteuthis magisterial (Berry 1913)). We quantified how digestibility was affected by proximate composition of the diet (%lipid or protein), levels of food mass and macronutrient intake, and tested for any potential benefit of multi-species diets. Overall, digestibility of both protein and lipid were high across diets, although macronutrient retention of lipids (96.0–98.4%) was significantly higher than protein (95.7–96.7%) for all but the two highest protein diets. Increased levels of protein intake resulted in increased protein retention, but decreased lipid digestibility. There was no evidence that mixed-species diets provide greater macronutrient digestibility over single-species diets. The results suggest that high to moderate lipid diets are more beneficial to northern fur seals as they lead to increased levels of lipid retention without large decreases in protein digestibility. This raises concerns that dietary factors may be contributing to the population declines of northern fur seals in the Bering Sea.

keywords     Northern fur seal, Callorhinus ursinus, diet composition, macronutrients, lipid digestibility, protein digestibility

abstract
As zooplanktivorous predators, bowhead whales (Balaena mysticetus) must routinely locate patches of prey that are energy-rich enough to meet their metabolic needs. However, little is known about how the quality and quantity of prey might influence their feeding behaviours. We addressed this question using a new approach that included: 1) multi-scale biologging and unmanned aerial system observations of bowhead whales in Cumberland Sound, Nunavut (Canada), and 2) an optical plankton counter (OPC) and net collections to identify and enumerate copepod prey species through the water column. The OPC data revealed two prey layers comprised almost exclusively of lipid-rich calanoid copepods. The deep layer contained fewer, but larger, particles (10% greater overall biomass) than the shallow prey layer. Dive data indicated that the whales conducted long deep Square-shaped dives (80% of dives; averaging depth of 260.4 m) and short shallow Square-shaped dives (16%; averaging depth of 22.5 m) to feed. The whales tended to dive proportionally more to the greater biomass of zooplankton that occurred at depth. Combining behavioural recordings with prey sampling showed a more complex feeding ecology than previously understood, and provides a means to evaluate the energetic balance of individuals under current environmental conditions.

keywords     bowhead whales, foraging

abstract
Climate change may affect the foraging success of bowhead whales Balaena mysticetus by altering the diversity and abundance of zooplankton species available as food. However, assessing climate-induced impacts first requires documenting feeding conditions under current environmental conditions. We collected seasonal movement and dive-behaviour data from 25 Eastern Canada-West Greenland bowheads instrumented with time-depth telemetry tags and used state-space models to examine whale movements and dive behaviours. Zooplankton samples were also collected in Cumberland Sound (CS) to determine species composition and biomass. We found that CS was used seasonally by 14 of the 25 tagged whales. Area-restricted movement was the dominant behaviour in CS, suggesting that the tagged whales allocated considerable time to feeding. Prey sampling data suggested that bowheads were exploiting energy-rich Arctic copepods such as Calanus glacialis and C. hyperboreus during summer. Dive behaviour changed seasonally in CS. Most notably, probable feeding dives were substantially shallower during spring and summer compared to fall and winter. These seasonal changes in dive depths likely reflect changes in the vertical distribution of calanoid copepods, which are known to suspend development and overwinter at depth during fall and winter when availability of their phytoplankton prey is presumed to be lower. Overall, CS appears to be an important year-round foraging habitat for bowheads, but is particularly important during the late summer and fall. Whether CS will remain a reliable feeding area for bowhead whales under climate change is not yet known.

keywords     Climate change, zooplankton, prey availability, foraging behavior, biologging, state-space model, bowhead whale, copepods, Calanus

abstract
As an annual ice-associated species, bowhead whales (Balaena mysticetus) are known to move northward in mid-to-late March and southward in early winter while following the annual cycle of sea ice decay and formation. We sought to determine when and where different demographic groups of Eastern Canada-West Greenland bowhead whales foraged throughout their range and what seasonal patterns occurred in their migratory and residency behaviour over a 16-year time period (2001-2016). Fifty-nine bowhead whales were equipped with satellite telemetry tags and hierarchical switching-state-space models (HSSSM) were used to infer probable foraging and travelling behaviour. Overall, 18,294 locations were predicted with the HSSSM and 70% of the locations (n = 12,784) were associated with probable foraging behaviour and 15% (n = 2709) included movements consistent with travelling behaviour. Both males and females were found to reside in Hudson Strait during winter. Females showed a slight preference for more northern regions (e.g. Gulf of Boothia) for feeding during summer compared with males who appeared to spend more time in more southern foraging grounds (e.g. Cumberland Sound). Females in Gulf of Boothia were significantly larger than females in Cumberland Sound but males were of comparable sizes in both regions. Lancaster Sound had the lowest occupancy, representing less than 0.8% of all HSSSM locations (n = 154) suggesting that this area may not be preferred by subadult male or female bowhead whales. Understanding whale movement behaviour will assist in anticipating patterns in distribution shifts associated with warming.

abstract
Physiology places constraints on an animal’s ability to forage and those unable to adapt to changing conditions may face increased challenges to reproduce and survive. As the global marine environment continues to change, small, air-breathing, endothermic marine predators such as otariids (fur seals and sea lions) and particularly females and juveniles may experience increased difficulties in successfully obtaining adequate food resources. We explored whether physiological limits of female otariids may be innately related to body morphology (fur seals vs sea lions) and/or dictate foraging strategies (epipelagic vs mesopelagic or benthic). We conducted a systematic review of the increased body of literature since the original reviews of Costa et al. (2004) and Arnould and Costa (2006) on behavioural (dive duration and depth) and physiological (total body oxygen stores and diving metabolic rates) parameters. We also estimated calculated aerobic dive limit (cADL - estimated duration of aerobic dives) for species, and used simulations to predict the proportion of dives that exceeded the cADL. We then tested whether body morphology or foraging strategy were the primary predictors of these behavioural and physiological characteristics. We found that foraging strategy more than morphology was a better predictor of most parameters, including whether a species was more likely to exceed their cADL during a dive and the ratio of dive time to cADL. This suggests that benthic divers are more likely to be foraging at their physiological capacity. For species operating near their physiological capacity (regularly exceeding their cADL), the ability to switch strategies is limited as the cost of foraging deeper and longer is disproportionally high. It is proposed that some otariids may not have the ability to switch foraging strategies and so be unable adapt to a changing oceanic eco

keywords     otariid, aerobic dive limit, prey availability, meta analysis, diving

abstract
Populations of Chinook (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) have experienced significant declines in abundance and productivity over the last 50 years in the Salish Sea as harbour seals (Phoca vitulina) recovered from hunting and culling. Some have hypothesized that increased predation by seals may be responsible for the declines in salmon survival, and their failure to recover after reductions in fishing effort. However, it is not known if these correlations exist for every population of salmon in the Salish Sea, or how many young Chinook and coho salmon are consumed by seals each year. I developed mathematical and statistical models to investigate the potential causal relationship between seal predation and declines in Chinook and coho salmon populations in the Salish Sea. I also used simulation modeling to evaluate outcomes that may result if managers reduced British Columbia’s harbour seal population to promote the recovery of salmon populations. I found that harbour seal densities were strongly negatively associated with productivity of most wild Chinook salmon populations in the Salish Sea and Washington Coast that were included in the study. Integrating recently collected seal diet data with a novel predation model indicates that large numbers of juvenile Chinook and coho salmon are eaten by seals, and that predation-related mortality has likely increased significantly over the last 50 years. The results of my simulation model suggest both lethal removals and contraception could reduce the seal population, but that important tradeoffs exist between the two approaches. Overall, my findings increase understanding of the role that marine mammal predation plays in the early marine life stage of juvenile salmon, and identifies potential outcomes and tradeoffs of actively managing predator populations.

keywords     predation, harbor seal, salmon, coho, Chinook, culling, hunting, modelling, hatcheries, diet, contraception, juvenile salmon, smolts, management

abstract
Carnivores come into conflict with humans when they cause damage to livestock, crops and other prop­erty. However, conflict is not only a land-based issue. As in terrestrial settings, human-wildlife conflict in the marine environment can have signif­icant financial repercussions and present animal wel­fare issues. To encourage sharing of knowledge on alternative approaches to managing wildlife conflict situations, a work­shop entitled Predator controls: lessons from land to sea was convened at the World Marine Mammal Con­ference in Barcelona, Spain in December 2019. Workshop participants concluded that: 1. Whilst there appears to be little transfer of an­ti-predator technologies between land and sea, people who farm and fish have common issues in­cluding ensuring the effectiveness of the measures deployed. This warrants a formal assessment of the common issues and solutions and a proper assess­ment of their welfare implications. 2. The welfare implications of conflict mitigation methods concerned many attending the workshop. How control methods impact predator welfare de­pends on the method used and how it is applied. 3. Standard protocols to assess the welfare and effec­tiveness of conflict mitigation techniques need to be developed and endorsed by the international community and could apply equally to land and sea situations. The approach used by Sharp and Saunders (2011) was noted as promising, as is the welfare assessment tool developed by the Interna­tional Whaling Commission. 4. Reducing conflict requires a thorough under­standing of the situation, including socio-eco­nomic aspects, determining whether the conflict is limited to individual problem animals or is more pervasive and evaluating how the problem at the site has developed. In addition, it is necessary to determine whether the conflict is more prevalent at a particular time of year, in a particular location or under certain ecological conditions or geopo­litical circumstances. Conflict resolution requires gathering as much in­formation as possible about the conflict in order to take appropriate actions and is an area where marine experts can learn from the experiences of terrestrial experts and vice versa. For this reason, providing plat­forms to marine and terrestrial experts to exchange knowledge and experience can benefit the conser­vation and welfare of wild predators on land and in the sea.

abstract
An array of foragers prey on salmon in rivers and estuaries while salmon smolts out-migrate from their natal streams-and may account, in part, for the poor returns of adult salmon to the Salish Sea. However, the Pacific great blue heron (Ardea herodias fanning) has not been identified as a predator of smolts despite being regularly seen near salmon streams. I investigated the role that herons may be playing in the depredation of salmon by scanning fecal remains under heron nests for Passive Integrated Transponder (PIT) tags that had been implanted in wild and hatchery-reared salmon smolts from 2008-2018. These nests were located in three heron rookeries that were within 35 km of the mouth of the Cowichan, Big Qualicum, and Capilano Rivers. Using a mobile PIT antenna, I recovered 1,199 smolt tags, representing a minimum annual predation rate of 0.3-1.3% of all smolts in the three rivers. Correcting for tags consumed by herons and defecated outside of the rookery raised the estimated proportion of smolts to 0.7-3.2% of the outmigrating fish, but predation rates as high as 6% were documented during a low river-flow year in the Cowichan River. The distribution and timing of tag depositions under the heron nests indicated that most great blue herons prey on salmon smolts and that consumption occurs in late spring during the chick-rearing phase of the breeding season. Energetic analyses suggest that smolt consumption provides a substantial proportion of the heron chick diet during a time of peak energy demand. Predation on smolts occurred primarily in the lower rivers and upper estuaries. Smaller salmon smolts were significantly more susceptible to heron predation in all systems, and predation rates were comparable between wild and hatchery-reared smolts. Recovering so many tags from smolts at heron rookeries was unexpected and indicates that great blue herons are a new predator of wild and hatchery-reared juvenile salmon. Locations of heron rookeries relative to salmon bearing rivers are likely good predictors of heron impacts on local salmon runs, and a potential means to assess coast-wide effects of great blue herons on salmon recovery.

abstract
The North Atlantic right whale (Eubalaena glacialis, NARW) is an endangered cetacean which faces population decline from anthropogenic activities. Climate change may also be adding pressure on population recovery by shifting distribution of their preferred prey, Calanus copepods. The Gulf of St. Lawrence (GSL) in eastern Canada has been used as a foraging ground by a large proportion of the NARW population in recent years (at least from 2015 to present). Given the motivation to better understand NARW contemporary habitat use patterns and propose recovery measures for this population, we used a mechanistic modeling approach to predict areas that hold foraging potential in the GSL. We first assessed the overall annual energetic costs incurred by an adult female NARW in one of three reproductive states, and determined the theoretical prey densities required to sustain energy demand. We used a 12-year data set describing the abundance and three-dimensional distribution of late-stage Calanus copepods in the GSL coupled to a foraging bioenergetics model to identify potentially suitable foraging areas for NARW. Results show interannual variations in the spatial distribution and quantity of suitable habitat, with a decreasing amount of habitat available for resting, pregnant and lactating females, respectively. Suitable prey densities for foraging NARW were found in nearly all areas of the GSL that were surveyed for copepods, in one year or another, with a greater frequency of suitable prey densities identified in the southern GSL. Yearly maps of suitable foraging habitat for NARW were superimposed to identify areas that showed temporal persistence; the southern GSL (from Shediac Valley east to the Magdalen Islands) had suitable prey densities for all three reproductive states in most (≥ 6) years of the study period. For resting and pregnant females, other potential areas of foraging importance included offshore of Chaleurs Bay as well as the southern slope of the Laurentian Channel north of the Magdalen Islands. These findings highlight areas where NARWs may occur based on habitat modelled foraging value, and emphasize the need to survey offshore, under-studied regions in the GSL to better characterize NARW occurrence and habitat use patterns.

abstract
The Steller sea lion is the largest member of the Otariidae family and is found in the coastal waters of the northern Pacific Rim. Here, we present the Steller sea lion genome, determined through DNA sequencing approaches that utilized microfluidic partitioning library construction, as well as nanopore technologies. These methods constructed a highly contiguous assembly with a scaffold N50 length of over 14 megabases, a contig N50 length of over 242 kilobases and a total length of 2.404 gigabases. As a measure of completeness, 95.1% of 4104 highly conserved mammalian genes were found to be complete within the assembly. Further annotation identified 19,668 protein coding genes. The assembled genome sequence and underlying sequence data can be found at the National Center for Biotechnology Information (NCBI) under the BioProject accession number PRJNA475770.

keywords     Steller sea lion, genetics

abstract
Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released smolts as covariates in spatially-structured Bayesian hierarchical stock-recruitment models, we found significant negative correlations between seal densities and productivity of Chinook salmon (Oncorhynchus tshawytscha) for 14 of 20 wild Chinook populations in the Pacific Northwest. Changes in numbers of seals since the 1970s were associated with a 74% decrease (95% CI: -85%, -64%) in maximum sustainable yield in Chinook stocks. In contrast, hatchery releases were significantly correlated with Chinook productivity in only one of 20 populations. Our findings are consistent with recent research on predator diets and bioenergetics modeling that suggest there is a relationship between harbour seal predation on juvenile Chinook and reduced marine survival in parts of the eastern Pacific. Forecasting, assessment, and recovery efforts for salmon populations of high conservation concern should thus consider including biotic factors, particularly predator-prey interactions.

keywords     salmon, seal density, hatchery

abstract
Marine mammal diving behaviour is influenced by multiple physiological processes, both at depth and at the surface. To date, the majority of research in diving physiology has focused solely on how quickly marine mammals utilize their O2 during a dive, as seen in the numerous studies of the aerobic dive limit (ADL) and calculated aerobic dive limit (cADL). In this thesis I investigated other physiological limits, namely how long it takes for marine mammals to recover after a dive, and how these animals transition between aerobic and anaerobic metabolism at depth. Specifically, I 1) determined how post-dive rates of O2 and CO2 gas exchange are affected by dive behaviour, and 2) measured how lactate accumulates with increased dive time, and examined how this indicator of metabolic transition affected post-dive recovery times. To measure gas exchange, I used flow-through respirometry to determine the time required for Steller sea lions (Eumetopias jubatus) to reach within 5% of stable rates of O2 uptake and CO2 excretion following a dive. These times were interpreted as the O2 and CO2 recovery times, respectively. CO2 recovery time was longer and became more extended with increasing dive time when compared to O2, requiring an extra 44 sec per minute submerged for CO2 as opposed to 33 sec per minute submerged for O2. This indicates that recovery time was limited by CO2 as opposed to O2, and this difference became greater with increased dive time. Contrary to traditional models, plasma lactate concentration was present even after short dives, and increased linearly with dive duration. Neither O2 nor CO2 recovery rates were affected by levels of blood lactate. This indicates that anaerobic metabolism may be used long before the body’s total O2 stores have been consumed. These results support the idea that there is not a distinct threshold between aerobic and anaerobic pathways, but rather a progressive transition, which casts doubt on the usual interpretations of the ADL and cADL. My thesis challenges long-held assertions in diving physiology, and underlines the need to further examine how CO2 and lactate accumulation may act as limits to diving behaviour.

keywords     Steller sea lion, metabolism, foraging

abstract
The hearts of marine mammals frequently sustain marked changes in heart rate and vascular resistance when diving. However, it is not known how marine mammal hearts facilitate these changes. I examined cardiac function and electrical activity of marine mammal hearts to understand how they might differ from terrestrial mammals. I measured electrocardiographic parameters in 8 Steller sea lions, 5 northern fur seals, and 1 walrus-and echocardiographic function in all 8 Steller sea lions. I also compiled electrocardiographic parameters from 17 species of marine mammals (including my measurements) for comparison with 50 species of terrestrial mammals. I found that atrial and ventricular depolarization are slower in marine mammals after accounting for differences in body mass-and that the left ventricle of Steller sea lions contracts less than expected for a mammal of that size. These differences in cardiac timing and function may reflect specialized adaptations for diving. Electrocardiographic measurements of Steller sea lions, northern fur seals, and a walrus also varied between species and among the individuals of each species. For example, sinus arrhythmias occurred in 5 out of 8 individual Steller sea lions, but not in northern fur seals or the walrus. Mean electrical axes were also unique to each individual and varied greatly. Measurements ranged from -124° to 80°-with 3 of the Steller sea lions having extreme right axis deviation (-111° to -124°). Echocardiographic measurements showed that left ventricular form was similar between Steller sea lions and terrestrial mammals, except that Steller sea lions have larger aortic roots and larger left ventricular end-systolic dimensions than terrestrial mammals. Overall, my results show that marine mammals have functionally similar hearts to terrestrial mammals with a number of notable differences that likely support anatomical adaptations to diving.

abstract
Calculating trophic levels is a necessary first step to quantify and understand trophic interactions between marine mammals and other species in marine ecosystems. This can be achieved using dietary information collected from stomachs and scats, or by measuring isotopic ratios contained in marine mammal tissues. These data indicate that marine mammals occupy a wide range of trophic levels beginning with dugong and manatees (trophic level 2.0), and followed by baleen whales (3.35), sea otters (3.45), seals (3.95), sea lions and fur seals (4.03), toothed whales (4.23) and polar bears (4.80). With the aid of ecosystem models and other quantitative analyses, the degree of competition can be quantified, and the consequences of changing predator-prey numbers can be predicted. These analyses show that many species of fish are major competitors of marine mammals. A number of field studies have also shown negative effects of reduced prey abundance on body size and survival of marine mammals. However, there are fewer examples of marine mammal populations affecting their prey due perhaps to the difficulty of monitoring such interactions, or to the complexity of most marine mammal food webs

abstract
This workshop assembled scientists and managers with technical expertise on seals, sea lions, and salmonids to identify and evaluate knowledge and uncertainties about the diets and population dynamics of pinnipeds (harbour seals, Steller sea lions, and California sea lions), as well as the impacts that pinnipeds may be having on salmonids in British Columbia and Washington State waters. The primary focal area was the Salish Sea, but included coastal Washington and British Columbia. Pinniped impacts in the Columbia River basin were not addressed. The workshop focused on what is known about predation by seals and sea lions on salmon-and how assumptions and uncertainties in the data affect the conclusions drawn to date about the effect of pinnipeds on salmon. This workshop was a first step in bringing together scientists and managers with pinniped and salmon expertise from Canada and the United States to identify and evaluate the impact that pinnipeds may be having on salmonids. It has identified the major knowledge gaps and need for focused research to address the key uncertainties that prevent drawing definitive conclusions about the role that pinnipeds play in the Salish Sea and their impact on other important ecosystem components such as salmon.

abstract
Decreased health may have lowered the birth and survival rates of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands over the past 30 yr. Reference ranges for clinical hematology and serum chemistry parameters needed to assess the health of wild sea lion populations are limited. Here, blood parameters were serially measured in 12 captive female Steller sea lions ranging in age from 3 wk to 16 yr to establish baseline values and investigate age-related changes. Whether diving activity affects hematology parameters in animals swimming in the ocean compared with animals in a traditional aquarium setting was also examined. Almost all blood parameters measured exhibited significant changes with age. Many of the age-related changes reflected developmental life history changes, including a change in diet during weaning, an improvement of diving capacity, and the maturity of the immune system. Mean corpuscular hemoglobin and mean corpuscular volume were also higher in the ocean diving group compared with the aquarium group, likely reflecting responses to increased exercise regimes. These data provide ranges of hematology and serum chemistry values needed to evaluate and compare the health and nutritional status of captive and wild Steller sea lions.

keywords     Diving, Eumetopias jubatus, hematology, marine mammal, serum chemistry, Steller sea lion

abstract
The Guadalupe fur seal Arctocephalus townsendi was intensively hunted and considered extinct by the end of the 1800s. However, small numbers (<20 seals) were reported on Guadalupe Island (Mexico) in the mid-1950s and were observed at a second location (San Benito Islands, Mexico) in the late 1990s. Sporadic counts at these 2 sites have followed a relatively rapid increase in numbers, but considerable uncertainty remains about the long-term viability of this recovering species. We performed a population viability analysis using historic seal counts from Guadalupe Island and the San Benito Islands to predict the probability of each colony (and both colonies combined) going extinct under 3 critical population threshold scenarios (100, 500, and 1000 seals). Using a diffusion approximation model, we found that the growth rates of the 2 colonies were similar (10−11% yr−1) and that the population totaled ~41 000 individuals in 2017 (⎯x = 40 614, 95% CI = 35 779−46 877). Guadalupe fur seals appear to be vulnerable to extreme climatic events. Of the 2 fur seal colonies, the San Benito Islands colony is less secure and is Endangered to Critically Endangered, depending on the quasi-extinction value used under the quantitative listing criteria established by the IUCN. In contrast, the Guadalupe Island colony and the 2 colonies combined meet the quantitative analysis criteria of Least Concern. Population viability analysis is an important component of assessing the status of wildlife populations and assisting nations and organizations in assigning appropriate categories of protection.

keywords     Guadalupe fur seal, population viability analysis, PVA, probability of extinction, endangered species, population trend, pinnipeds

abstract
Foraging strategies and their resulting efficiency (energy gain to cost ratio) affect animals' survival and reproductive success and can be linked to population dynamics. However, they have rarely been studied quantitatively in free-ranging animals. We investigated foraging strategies and efficiencies of wild northern fur seals Callorhinus ursinus during their breeding season to understand potential links to the observed population decline in the Bering Sea. We equipped 20 lactating females with biologgers to determine at-sea foraging behaviors. We measured energy expenditure while foraging using the doubly labeled water method, and energy gained using (1) the types and energy densities of prey consumed, and (2) the number of prey capture attempts (from acceleration data). Our results show that seals employed 2 foraging strategies. One group (40%) fed mostly in oceanic waters on small high energy-density prey, while the other (60%) stayed over the shallow continental shelf feeding mostly on larger, lower quality fish. Females foraging in oceanic waters captured 3 times more prey, and had double the foraging efficiencies of females that foraged on-shelf in neritic waters. However, neritic seals made comparatively shorter trips, and likely fed their pups ~20-25% more frequently. The presence of these strategies which either favor foraging efficiency (energy) or frequency of nursing (time) might be maintained in the population because they have similar net fitness outcomes. However, neither strategy appears to simultaneously maximise time and energy allocated to nursing, with potential impacts on the survival of pups during their first year at sea.

abstract
Most stocks of Atlantic cod (Gadus morhua) in the northwest Atlantic collapsed in the early 1990s, with little sign of recovery since then. In the southern Gulf of St. Lawrence (sGSL), the failed recovery is due to severe increases in the natural mortality of adult Atlantic cod. We examined the role of predation by grey seals (Halichoerus grypus) in this failed recovery by directly incorporating grey seal predation in the population model for Atlantic cod via a functional response. Estimated predation mortality of adult Atlantic cod increased sharply during the cod collapse and has continued to increase, comprising the majority of mortality since the early 2000's. While predation by grey seals appeared to play a minor role in the collapse of Atlantic cod, we found it to be the main factor preventing recovery. Our results are consistent with the hypothesis that failed recovery is due to predation-driven Allee effects, a demographic effect due to the decline in cod abundance and an emergent effect resulting from increasing grey seal abundance. Under current conditions, extirpation of sGSL Atlantic cod appears likely unless there is a large decline in the abundance of grey seals.

abstract
The field notes of Frachtenberg (1916) and others note that the Quileute had been practicing whaling since immemorial times. Additional historical and archaeological data confirm that the Quileute successfully hunted and consumed many of the same species taken by the Makah and Nuu-chah-nulth whale hunters during and before treaty times. The archaeological, historical, and ecological data are thus consistent with the Quileute hunters being exceptional seamen, navigators, and whalers.

keywords     whales, whaling, indigenous people, prehistoric, middens, gray whale, humpback whale, fin whale, blue whale, sperm whale, right whale

abstract
Animal-borne instruments have become a standard tool for collecting important data from marine mammals. However, few studies have examined whether placement of these data loggers affects the behavior and energetics of individual animals, potentially leading to biasing data. We measured the effect of two types of relatively small data loggers (<1% of animals

keywords     northern fur seals, Callorhinus ursinus, telemetry, bioenergetics, biologging, diving, swimming, marine mammal

abstract
Ecosystem-based management requires a clear understanding of marine ecosystem functioning, particularly the transfer of energy (consumption) to higher trophic levels. However, robust estimates of consumption are generally hampered by a dearth of data for predators (diet and abundance), and by methodological weaknesses. We undertook a comprehensive assessment of energy requirements and prey consumption for the 10 most abundant cetacean species in the Bay of Biscay (northeastern Atlantic Ocean, France) by combining recent data on their abundances from aerial surveys, and diets from stomach content analyses. We also incorporated functional considerations to group prey and address interspecific differences in the cost of living of cetaceans that are independent of body size. Species considered included harbour porpoise, common dolphins, striped dolphins, bottlenose dolphins, long-finned pilot whales, Risso's dolphins, sperm whales, Cuvier's beaked whales, minke whales and fin w hales. We used Monte Carlo resampling methods to estimate annual and seasonal (winter and summer) consumption over the continental shelf and slope

keywords     food webs, consumption, cetaceans, continental shelf, toothed whales, baleen whales

abstract
This workshop assembled scientists and managers with technical expertise on killer whales and Chinook salmon to identify and evaluate short-term management actions that might increase the immediate abundance and accessibility of Chinook salmon for southern resident killer whales, given the current size of Chinook salmon stocks. The workshop did not consider ways of producing more Chinook salmon (which will be the subject of a subsequent workshop), but rather considered ways of making more of the fish that are presently in the ocean available to southern resident killer whales (SRKW). Workshop participants presented and discussed technical information on the prey requirements of SRKW, the availability of Chinook salmon, and current protections for SRKW. Participants then split into four groups with an even distribution of expertise to evaluate three potential non- exclusive Management Actions: 1) Increase the abundance of Chinook for SRKW by reducing coast-wide fishery removals; 2) Increase the abundance of Chinook for SRKW by adjusting fishery removals at specific times and in specific areas of SRWK habitat; and 3) Increase the accessibility of Chinook by decreasing underwater noise and the physical presence of vessels where SRKW forage.

keywords     killer whales, southern resident, prey, availability, abundance, accessibility, noise, disturbance, fishing, commercial, recreational, Chinook, salmon

abstract
There is increasing evidence that predation by harbour seals (Phoca vitulina) on young salmon (smolts) out-migrating from rivers may be a significant source of mortality for coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) salmon populations in British Columbia. Studies supporting this have focused on documenting what and how much harbour seal populations eat - and the potential impact this has on salmon populations. However, little attention has been given to understanding where, when and how this predation occurs, and the extent to which it might be opportunistic or specialist feeding behaviour by a few or many individual seals. I documented the spatiotemporal foraging behaviour of harbour seals in the Salish Sea by equipping 17 seals with GPS loggers and Daily Diary tags - and tracking them before and after the release of thousands of coho and Chinook smolts from the Big Qualicum Hatchery. Reconstructing the high-resolution movements of the seals - and quantifying feeding using counts of prey chasing events (PCEs) detected by accelerometry - revealed that the Big Qualicum estuary was a feeding hotspot for 47.0% of the 17 tracked seals, but was relatively small geographically (accounting for 3% of PCEs) compared to the largest feeding area outside the estuary (26% of PCEs). Comparing the foraging behaviours of smolt specialists with non-specialist seals revealed 4 different foraging strategies. One consisted of seals (17.6%) that only fed on coho smolts and ignored Chinook in the river mouth, while a second group of seals (17.6%) appeared to target larger fish that preyed on Chinook smolts near the river mouth. The two other seal groups did not feed at the river mouth in association with the concentrated numbers of smolts, but either remained resident (52.9%) and fed near their main haul-out sites, or were transient (11.8%) and left the study area all together. My results suggest a high degree of individual foraging and diet specializations - and show that a small number of seals were specialized in consuming coho smolts, but did not appear to respond to the large pulse of the smaller bodied Chinook smolts. Such information concerning the fine-scale foraging behaviour of harbour seals in relation to pulses of out-migrating smolts can be used to design mitigation strategies to enhance coho and Chinook populations.

abstract
Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser devil rays Mobula cf. hypostoma, but their disc widths were between 207 and 230 cm, which is almost double the reported maximum disc width of 120 cm for this species. These morphometric data suggest that lesser devil rays are either larger than previously recognized or that these specimens belong to an unknown sub-species of Mobula in the Caribbean Sea. Better data are needed to describe the distribution, phenotypic variation and population structure of this poorly known species.

abstract
Bowhead whales (Balaena mysticetus) have a nearly circumpolar distribution, and occasionally occupy warmer shallow coastal areas during summertime that may facilitate molting. However, relatively little is known about the occurrence of molting and associated behaviors in bowhead whales. We opportunistically observed whales in Cumberland Sound, Nunavut, Canada with skin irregularities consistent with molting during August 2014, and collected a skin sample from a biopsied whale that revealed loose epidermis and sloughing. During August 2016, we flew a small unmanned aerial system (sUAS) over whales to take video and still images to: 1) determine unique individuals; 2) estimate the proportion of the body of unique individuals that exhibited sloughing skin; 3) determine the presence or absence of superficial lines representative of rock-rubbing behavior; and 4) measure body lengths to infer age-class. The still images revealed that all individuals (n = 81 whales) were sloughing skin, and that nearly 40% of them had mottled skin over more than two-thirds of their bodies. The video images captured bowhead whales rubbing on large rocks in shallow, coastal areas --likely to facilitate molting. Molting and rock rubbing appears to be pervasive during late summer for whales in the eastern Canadian Arctic.

abstract
1-Energy expenditure is an important component of foraging ecology, but is extremely difficult to estimate in free-ranging animals and depends on how animals partition their time between different activities during foraging. Acceleration data has emerged as a new way to determine energy expenditure at a fine scale but needs to be tested and validated in wild animals. 2-This study investigated whether vectorial dynamic body acceleration (VeDBA) could accurately predict the energy expended by marine predators during a full foraging trip. We also aimed to determine whether the accuracy of predictions of energy expenditure derived from acceleration increased when partitioned by different types of at-sea activities (i.e., diving, transiting, resting and surface activities) vs calculated activity-specific metabolic rates. 3-To do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20 Antarctic fur seals (Arctocephalus gazella) with GPS, time-depth recorders and tri-axial accelerometers, and obtained estimates of field metabolic rates using the doubly-labelled water (DLW) method. VeDBA was derived from tri-axial acceleration, and at-sea activities (diving, transiting, resting and surface activities) were determined using dive depth, tri-axial acceleration and traveling speed. 4-We found that VeDBA did not accurately predict the total energy expended by fur seals during their full foraging trips (R2 = 0.36). However, the accuracy of VeDBA as a predictor of total energy expenditure increased significantly when foraging trips were partitioned by activity and used activity-specific VeDBA paired with time activity budgets (R2 = 0.70). Activity-specific VeDBA also accurately predicted the energy expenditures of each activity independent of each other (R2 > 0.85). 5-Our study confirms that acceleration is a promising way to estimate energy expenditures of free-ranging marine mammals at a fine scale never attained before. However, it shows that it needs to be based on the time-activity budget that make up foraging trips rather than being derived as a single measure of VeDBA applied to entire foraging trips. Our activity-based method provides a cost-effective means to accurately calculate energy expenditures of fur seals using acceleration and time-activity budgets, a stepping stone for numerous other research fields.

keywords     Antarctic fur seal, Arctocephalus gazella, Callorhinus ursinus, diving, energy expenditure, foraging, metabolic rate, northern fur seal, time-activity budget

abstract
The efficiency with which individuals extract energy from their environment defines their survival and reproductive success, and thus their selective contribution to the population. Individuals that forage more efficiently (i.e., when energy gained exceeds energy expended) are likely to be more successful at raising viable offspring than individuals that forage less efficiently. Our goal was to test this prediction in large long-lived mammals under free-ranging conditions. To do so, we equipped 20 lactating Antarctic fur seals (Arctocephalus gazella) breeding on Kerguelen Island in the Southern Ocean with tags that recorded GPS locations, depth and tri-axial acceleration to determine at-sea behaviours and detailed time-activity budgets during their foraging trips. We also simultaneously measured energy spent at sea using the doubly-labeled water (DLW) method, and estimated the energy acquired while foraging from 1) type and energy content of prey species present in scat remains, and 2) numbers of prey capture attempts determined from head acceleration. Finally, we followed the growth of 36 pups from birth until weaning (of which 20 were the offspring of our 20 tracked mothers), and used the relative differences in body mass of pups at weaning as an index of first year survival and thus the reproductive success of their mothers. Our results show that females with greater foraging efficiencies produced relatively bigger pups at weaning. These mothers achieved greater foraging efficiency by extracting more energy per minute of diving rather than by reducing energy expenditure. This strategy also resulted in the females spending less time diving and less time overall at sea, which allowed them to deliver higher quality milk to their pups, or allowed their pups to suckle more frequently, or both. The linkage we demonstrate between reproductive success and the quality of individuals as foragers provides an individual-based quantitative framework to investigate how changes in the availability and accessibility of prey can affect fitness of animals.

keywords     foraging, energetics, pups, growth, biologging, doubly-labeled water, Antarctic fur seal, Arctocephalus gazella

abstract
Time and energy are the two most important currencies in animal bioenergetics. How much time animals spend engaged in different activities with specific energetic costs ultimately defines their likelihood of surviving and successfully reproducing. However, it is extremely difficult to determine the energetic costs of independent activities for free-ranging animals. In this study, we developed a new method to calculate activity-specific metabolic rates, and applied it to female fur seals. We attached biologgers (that recorded GPS locations, depth profiles, and triaxial acceleration) to 12 northern (Callorhinus ursinus) and 13 Antarctic fur seals (Arctocephalus gazella), and used a hierarchical decision tree algorithm to determine time allocation between diving, transiting, resting, and performing slow movements at the surface (grooming, etc.). We concomitantly measured the total energy expenditure using the doubly-labelled water method. We used a general least-square model to establish the relationship between time-activity budgets and the total energy spent by each individual during their foraging trip to predict activity-specific metabolic rates. Results show that both species allocated similar time to diving (~29%), transiting to and from their foraging grounds (~26-30%), and resting (~8-11%). However, Antarctic fur seals spent significantly more time grooming and moving slowly at the surface than northern fur seals (36% vs. 29%). Diving was the most expensive activity (~30 MJ/day if done non-stop for 24 hr), followed by transiting at the surface (~21 MJ/day). Interestingly, metabolic rates were similar between species while on land or while slowly moving at the surface (~13 MJ/day). Overall, the average field metabolic rate was ~20 MJ/day (for all activities combined). The method we developed to calculate activity-specific metabolic rates can be applied to terrestrial and marine species to determine the energetic costs of daily activities, as well as to predict the energetic consequences for animals forced to change their time allocations in response to environmental shifts.

keywords     Antarctic fur seal, Arctocephalus gazella, Callorhinus ursinus, diving, energy expenditure, foraging, metabolic rate, northern fur seal, time-activity budget

abstract
Accurately estimating predators' diets at relevant spatial and temporal scales is key to understanding animals' energetics and fitness, particularly in populations whose decline might be related to their diet such as northern fur seals Callorhinus ursinus. Our goals were to improve the accuracy of diet estimates and extend understanding of feeding ecology by combining 2 scat-based methods of diet determination (hard-part identification and DNA-metabarcoding) with stable isotope measurements and individual behavioural data. We collected 98 scats on a northern fur seal breeding colony. We also tracked 20 females with biologgers, and took blood samples to determine δ13C and δ15N values as proxies for seal foraging habitat and diet. Results show that diet composition from hard-parts analysis corresponded well with DNA results, with DNA yielding a greater diversity of prey species at a finer taxonomic level. Overall, scat-based methods showed that seals mostly fed on neritic shelf-associated prey. Cluster analyses of combined hard-parts and DNA results however identified 2 diet groups, one mostly neritic and the other mostly pelagic. Stable isotopes and behavioural data revealed that 40% of seals fed in oceanic waters on pelagic prey. This is more than indicated by scat-based analyses, which are likely biased towards animals foraging closest to the colony and underestimate some dietary specializations within the population. Consequently, the combination of multiple methods for diet identification with at-sea tracking of individuals can help identify and quantify specialist groups within a population and provide a wider spatial and temporal ecological context for dietary analysis.

abstract
Direct measures of energy expenditure are difficult to obtain in marine mammals, and accelerometry may be a useful proxy. Recently its utility has been questioned as some analyses derived their measure of activity level by calculating the sum of accelerometry-based values and then comparing this summation to summed (total) energy expenditure (the so-called 'time trap'). To test this hypothesis, we measured oxygen consumption of captive fur seals and sea lions wearing accelerometers during submerged swimming and calculated total and rate of energy expenditure. We compared these values with two potential proxies of energy expenditure derived from accelerometry data: flipper strokes and dynamic body acceleration (DBA). Total number of strokes, total DBA, and submergence time all predicted total oxygen consumption (sVO2 ml kg−1). However, both total DBA and total number of strokes were correlated with submergence time. Neither stroke rate nor mean DBA could predict the rate of oxygen consumption (sV.O2 ml min−1 kg−1). The relationship of total DBA and total strokes with total oxygen consumption is apparently a result of introducing a constant (time) into both sides of the relationship. This experimental evidence supports the conclusion that proxies derived from accelerometers cannot estimate the energy expenditure of marine mammals.

keywords     energy expenditure, accelerometers, Steller sea lions

abstract
Energy expenditure of free-living fur seals and sea lions is difficult to measure directly, but may be indirectly derived from flipper stroke rate. We filmed 10 captive otariids swimming with accelerometers either attached to a harness (Daily Diary: sampling frequency 32Hz, N = 4) or taped to the fur (G6a+: 25Hz, N = 6). We used down sampling to derive four recording rates from each accelerometer (Daily Diary: 32, 16, 8, 4Hz; G6a+: 25, 20, 10, 5Hz). For each of these sampling frequencies we derived 20 combinations of two parameters (RMW - the window size used to calculate the running mean, and m – the minimum number of points smaller than the local maxima used to detect a peak), from the dynamic acceleration of x, z and x+z, to estimate stroke rate from the accelerometers. These estimates differed by up to ~20% in comparison to the actual number of foreflipper strokes counted from videos. RMW had little effect on the overall differences, nor did the choice of axis used to make the calculations (x, z or x+z), though the variability was reduced when using x+z. The best m varied depending on the axis used and the sampling frequency, where a larger m was needed for higher sampling frequencies. This study demonstrates that when parameters are appropriately tuned, accelerometers are a simple yet valid tool for estimating the stroke rates of swimming otariids.

keywords     otariid, swim mechanics, stroke rate, accelerometer, energetics, biologger

abstract
Marine mammals are characterized as having physiological specializations that maximize the use of oxygen stores to prolong time spent under water. However, it has been difficult to undertake the requisite controlled studies to determine the physiological limitations and trade-offs that marine mammals face while diving in the wild under varying environmental and nutritional conditions. For the past decade, Steller sea lions (Eumetopias jubatus) trained to swim and dive in the open ocean away from the physical confines of pools participated in studies that investigated the interactions between diving behaviour, energetic costs, physiological constraints, and prey availability. Many of these studies measured the cost of diving to understand how it varies with behaviour and environmental and physiological conditions. Collectively, these studies show that the type of diving (dive bouts or single dives), the level of underwater activity, the depth and duration of dives, and the n utritional status and physical condition of the animal affect the cost of diving and foraging. They show that dive depth, dive and surface duration, and the type of dive result in physiological adjustments (heart rate, gas exchange) that may be independent of energy expenditure. They also demonstrate that changes in prey abundance and nutritional status cause sea lions to alter the balance between time spent at the surface acquiring oxygen (and offloading CO2 and other metabolic by-products) and time spent at depth acquiring prey. These new insights into the physiological basis of diving behaviour further our understanding of the potential scope for behavioural responses of marine mammals to environmental changes, the energetic significance of these adjustments, and the consequences of approaching physiological limits.

abstract
Knowing the species and life stages of prey that predators consume is important for understanding the impacts that predation may have on prey populations, but traditional methods for determining diets often cannot provide sufficient detail. We combined data from two methods of scat analysis (DNA metabarcoding and morphological prey ID) to quantify the species and life stages of salmon (Oncorhynchus spp.) consumed by harbour seals (Phoca vitulina) in the Strait of Georgia, Canada, where juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon survival is poor. Harbour seals primarily consumed adult salmon of lesser conservation concern in the fall (August-November): chum (Oncorhynchus keta: 18.4%), pink (Oncorhynchus gorbuscha: 12.6%), sockeye (Oncorhynchus nerka: 7.4%), Chinook (7.1%), and coho (1.8%). However, the opposite species trend occurred during the spring when seals preferred juvenile salmon of greater conservation concern (April july): coho (2.9%), Chinook (2.9%), sockeye (2.5%), pink (1.4%), and chum (0.8%)percentages that can equate to many individuals consumed. Our data suggest that harbour seals select juveniles of salmon species that out-migrate at ages >1 year and provide evidence of a potential causal relationship between harbour seal predation and juvenile salmon survival trends.

keywords     seals, predation, salmon, coho, Chinook, diet

abstract
Polar oceans are poorly monitored despite the important role they play in regulating Earth's climate system. Marine mammals equipped with biologging devices are now being used to fill the data gaps in these logistically difficult to sample regions. Since 2002, instrumented animals have been generating exceptionally large data sets of oceanographic CTD casts (>500,000 profiles), which are now freely available to the scientific community through the MEOP data portal (http://meop.net). MEOP (Marine Mammals Exploring the Oceans Pole to Pole) is a consortium of international researchers dedicated to sharing animal-derived data and knowledge about the polar oceans. Collectively, MEOP demonstrates the power and cost-effectiveness of using marine mammals as data-collection platforms that can dramatically improve the ocean observing system for biological and physical oceanographers. Here, we review the MEOP program and database to bring it to the attention of the international community.

abstract
Background: We sought to quantitatively describe the fine-scale foraging behavior of northern resident killer whales (Orcinus orcas), a population of fish-eating killer whales that feeds almost exclusively on Pacific salmon (Oncorhynchus spp.). To reconstruct the underwater movements of these specialist predators, we deployed 34 biologging Dtags on 32 individuals and collected high-resolution, three-dimensional accelerometry and acoustic data. We used the resulting dive paths to compare killer whale foraging behavior to the distributions of different salmonid prey species. Understanding the foraging movements of these threatened predators is important from a conservation standpoint, since prey availability has been identified as a limiting factor in their population dynamics and recovery. Results: Three-dimensional dive tracks indicated that foraging (N = 701) and non-foraging dives (N = 10,618) were kinematically distinct (Wilks

keywords     Foraging, Movement, Diving behavior, Biologging, Dtag, Accelerometry, Killer whale, Orcinus orca, Pacific salmon

abstract
Protozoal infections have been widely documented in marine mammals and may cause morbidity and mortality at levels that result in population level effects. The presence and potential impact on the recovery of endangered Hawaiian monk seals Neomonachus schauinslandi by protozoal pathogens was first identified in the carcass of a stranded adult male with disseminated toxoplasmosis and a captive monk seal with hepatitis. We report 7 additional cases and 2 suspect cases of protozoal-related mortality in Hawaiian monk seals between 2001 and 2015, including the first record of vertical transmission in this species. This study establishes case definitions for classification of protozoal infections in Hawaiian monk seals. Histopathology and immunohistochemistry were the primary diagnostic modalities used to define cases, given that these analyses establish a direct link between disease and pathogen presence. Findings were supported by serology and molecular data when available. Tox oplasma gondii was the predominant apicomplexan parasite identified and was associated with 100% of mortalities (n = 8) and 50% of suspect cases (n = 2). Incidental identification of sarcocysts in the skeletal muscle without tissue inflammation occurred in 4 seals, including one co-infected with T. gondii. In 2015, 2 cases of toxo-plasmosis were identified ante-mortem and shared similar clinical findings, including hematological abnormalities and histopathology. Protozoal-related mortalities, specifically due to toxoplasmosis, are emerging as a threat to the recovery of this endangered pinniped and other native Hawaiian taxa. By establishing case definitions, this study provides a foundation for measuring the impact of these diseases on Hawaiian monk seals.

keywords     Protozoa, Mortality, Pathology, Immunohistochemistry, Toxoplasma gondii, Sarcocystis, Pinniped

abstract
Bioenergetic studies can quantify the conversion of chemical energy contained in food to biologically useful energy to understand how changes in diet quality and quantity affect overall energy budgets and nutritional status. However, chemical energy is intrinsically linked to the macronutrients contained in food (i.e., lipid and protein) in terms of energetic density and digestive efficiency. For northern fur seals (Callorhinus ursinus) it is unknown how efficiently they transform dietary gross energy to net energy. I fed six trained adult female fur seals eight experimental diets composed of four prey species (capelin, walleye pollock, Pacific herring, and Magister squid), alone or combined. I measured the fur seals' digestive efficiency for energy and macronutrients across diets. I also investigated the effect of dietary intake on digestive efficiency, and tested the hypothesis that mixed-species diets provide a greater nutritional return than equivalent single-species diets. I quantified net energy uptake by measuring excreta energy loss and measuring heat increment of feeding. My results revealed significant differences between digestive parameters across diets. I found that digestible energy (95.9-96.7%) was negatively affected by both ingested mass and dietary crude protein. Furthermore, urinary energy loss (9.3-26.7%) increased significantly with increases in dietary crude protein. I also found that the heat increment of feeding (4.3-12.4%) increased with decreasing dietary lipid content. Overall, net energy gain (57.9-83.0%) was positively correlated with lipid content. I found that macronutrient digestibility differed across diets and that, overall, lipids were more digestible (96.0-98.4%) than crude proteins (95.7-96.7%). Also, dietary protein influenced the ability of fur seals to digest lipids and proteins. Overall, my results demonstrate that low lipid prey not only contain less gross energy, but result in proportionally lower net energy gain following digestion, partly due to decreasing digestibility of lipids in high protein diets. I also found that, counter to predictions, mixed-species diets do not provide fur seals with greater energetic or macronutrient gains than single-species diets. These findings contribute to understanding the nutritional ecology of northern fur seals and the impact that changes in diet can have on the fur seals' nutritional state.

abstract
Understanding whether northern fur seals (Callorhinus ursinus (L., 1758)) are negatively affected by changes in prey quality or diversity could provide insights into their on-going population decline in the central Bering Sea. We investigated how six captive female fur seals assimilated energy from eight different diets consisting of four prey species (walleye pollock (Gadus chalcogrammus Pallas, 1814, formerly Theragra chalcogrammus (Pallas, 1814)), Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847), capelin (Mallotus villosus (Muller, 1776)), and magister armhook squid (Berryteuthis magister (Berry, 1913))) fed alone or in combination. Net energy was quantified by measuring fecal energy loss, urinary energy loss, and heat increment of feeding. Digestible energy (95.9%-96.7%) was high (reflecting low fecal energy loss) and was negatively affected by ingested mass and dietary protein content. Urinary energy loss (9.3%-26.7%) increased significantly for high-protein diets. Heat increment of feeding (4.3%-12.4%) was significantly lower for high-lipid diets. Overall, net energy gain (57.9%-83.0%) was affected by lipid content and varied significantly across diets. Mixed-species diets did not provide any energetic benefit over single-species diets. Our study demonstrates that diet quality was more important in terms of energy gain than diet diversity. These findings suggest that fur seals consuming low-quality prey in the Bering Sea would be more challenged to obtain sufficient energy to satisfy energetic and metabolic demands, independent of high prey abundance.

keywords     northern fur seal, Callorhinus ursinus, net energy, mixed-species diets, diet quality

abstract
Recent studies of stranded marine mammals indicate that exposure to underwater military sonar may induce pathophysiological responses consistent with decompression sickness (DCS). However, DCS has been difficult to diagnose in marine mammals. We investigated whether blood microparticles (MPs, measured as number/l plasma), which increase in response to decompression stress in terrestrial mammals, are a suitable biomarker for DCS in marine mammals. We obtained blood samples from trained Steller sea lions (Eumetopias jubatus, 4 adult females) wearing time-depth recorders that dove to predetermined depths (either 5 or 50 meters). We hypothesized that MPs would be positively related to decompression stress (depth and duration underwater). We also tested the effect of feeding and exercise in isolation on MPs using the same blood sampling protocol. We found that feeding and exercise had no effect on blood MP levels, but that diving caused MPs to increase. However, blood MP levels did not correlate with diving depth, relative time underwater, and presumed decompression stress, possibly indicating acclimation following repeated exposure to depth.

abstract
Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has not been validated on free-ranging otariids (fur seals and sea lions). Our goal was to investigate how well flipper strokes correlate with energy expenditure in 33 foraging northern and Antarctic fur seals equipped with accelerometers, GPS, and time-depth recorders. We concomitantly measured field metabolic rates with the doubly-labeled water method and derived activity-specific energy expenditures using fine-scale time-activity budgets for each seal. Flipper strokes were detected while diving or surface transiting using dynamic acceleration. Despite some inter-species differences in flipper stroke dynamics or frequencies, both species of fur seals spent 3.79 ± 0.39 J/kg per stroke and had a cost of transport of ~1.6-1.9 J/kg/m while diving. Also, flipper stroke counts were good predictors of energy spent while diving (R2 = 0.76) and to a lesser extent while transiting (R2 = 0.63). However, flipper stroke count was a poor predictor overall of total energy spent during a full foraging trip (R2 = 0.50). Amplitude of flipper strokes (i.e., acceleration amplitude x number of strokes) predicted total energy expenditure (R2 = 0.63) better than flipper stroke counts, but was not as accurate as other acceleration-based proxies, i.e. Overall Dynamic Body Acceleration.

keywords     accelerometer, energy expenditure, field metabolic rate, doubly-labelled-water, flipper strokes, cost of transport, ODBA, VeDBA, northern fur seal, Antarctic fur seal

abstract
Bayesian Melding (BM) and downscaling are two Bayesian approaches commonly used to combine data from different sources for statistical inference. We extend these two approaches to combine accurate but sparse direct observations with another set of high-resolution but biased calculated observations. We use our methods to estimate the path of a moving or evolving object and apply them in a case study of tracking northern fur seals. To make the BM approach computationally feasible for high dimensional (big) data, we exploit the properties of the processes along with approximations to the likelihood to break the high dimensional problem into a series of lower dimensional problems. To implement the alternative, downscaling approach, we use R-INLA to connect the two sources of observations via a linear mixed effect model. We compare the predictions of the two approaches by cross-validation as well as simulations. Our results show that both approaches yield similar results— both provide accurate, high resolution estimates of the atea locations of the northern fur seals, as well as Bayesian credible intervals to characterize the uncertainty about the estimated movement paths.

keywords     Bayesian Melding, Downscaling, Bio-logging, Conditional independence, INLA, Dead-Reckoning, Tracking, Marine mammals

abstract
Aerial surveys are sometimes used to assess the densities of wide-ranging whales, as well as changes in their distributions in response to human activity. Such surveys also provide data used to estimate numbers of animals exposed to different received levels of seismic sound, as required by regulators. However, estimates of abundance are often biased because they fail to account for the effects of seismic operations on the surfacing and diving behavior of whales. Our objective was to determine the extent to which analyses of the distribution of bowhead whales Balaena mysticetus are affected by changes in visual 'availability' caused by seismic operations. We used aerial survey data collected during seismic operations in the Alaskan Beaufort Sea from late August to early October 2008 and fit spatial density surface models to bowhead sighting data to predict whale density in an ensonified area. We also incorporated availability correction factors to determine the sensitivity of density estimates to changes in surfacing and diving behavior caused by seismic operations. The influence of altered whale behavior was then evaluated by comparing a series of realistic simulated scenarios in which models incorporated undisturbed or seismic disturbance-related correction factors. Results suggest that the numbers of bowhead whales present in the vicinity of seismic operations during the bowhead autumn migration are underestimated if the behavioral effects of seismic operations on whales are ignored. Our study highlights the importance of accounting for changes in whale behavior that can affect sightability when estimating numbers and distribution of whales in the vicinity of industrial activity.

keywords     Bowhead whale, Seismic survey, Distance sampling, Beaufort Sea, Availability, g(0), Alaska, Spatial models, Behavior, Generalized additive model

abstract
DNA metabarcoding is a powerful new tool allowing characterization of species assemblages using high-throughput amplicon sequencing. The utility of DNA metabarcoding for quantifying relative species abundances is currently limited by both biological and technical biases which influence sequence read counts. We tested the idea of sequencing 50/50 mixtures of target species and a control species in order to generate relative correction factors (RCFs) that account for multiple sources of bias and are applicable to field studies. RCFs will be most effective if they are not affected by input mass ratio or co-occurring species. In a model experiment involving three target fish species and a fixed control, we found RCFs did vary with input ratio but in a consistent fashion, and that 50/50 RCFs applied to DNA sequence counts from various mixtures of the target species still greatly improved relative abundance estimates (e.g., average per species error of 19 ± 8% for uncorrected versu s 3 ± 1% for corrected estimates). To demonstrate the use of correction factors in a field setting, we calculated 50/50 RCFs for 18 harbour seal (Phoca vitulina) prey species (RCFs ranging from 0.68 to 3.68). Applying these corrections to field-collected seal scats affected species percentages from individual samples (Δ 6.7 ± 6.6%) more than population level species estimates (Δ 1.7 ± 1.2%). Our results indicate that the 50/50 RCF approach is an effective tool for evaluating and correcting biases in DNA metabarcoding studies. The decision to apply correction factors will be influenced by the feasibility of creating tissue mixtures for the target species, and the level of accuracy needed to meet research objectives.

keywords     DNA metabarcoding, high-throughput amplicon sequencing, harbor seal, Phoca vitulina, diets, prey consumption, diet reconstruction, scats, fecal samples

abstract
The ultimate solution to protecting fish farms and fishing gear from marine mammals is not yet at hand - and there is unlikely to be a one-size-fits-all solution. Protecting fish raised in open-ocean meshed pens will likely prove to be a two-stepped process that begins with using physical barriers around pens to prevent predators from obtaining the fish (such as predator exclusion nets) - and turning to sound (such as acoustic deterrence) as the second step to quickly push back any individuals that breach the protective perimeter. Some capture fisheries may be able to protect their catches using barriers (such as traps instead of hooks) or using smart fishing techniques (such as shorter soak times, or modified hauling techniques), while others might find electrified nets and acoustic deterrence are effective in scaring predators in the short-term. Unfortunately, all technologically-based deterrence methods are likely to fail in the long-term as animals adapt to prolonged stimulus and find the rewards they receive to be greater than the price they pay to obtain them. New technologies often also equate to new problems and conflicts - it is just that no one knows yet what they are until the technology has been fully implemented. Thus, simple (but perhaps initially expensive) options that prevent predators from seeing or accessing the fish intended for human consumption are likely to be the most successful, while the technologically based solutions are likely to be most successful when used sparingly. Using one-two punch solutions that combine the two methods would seem to have the greatest likelihood of successfully reducing or removing conflicts between fisheries and marine mammals. They may also ultimately yield the peace of mind that society and those whose livelihoods depend on harvesting marine species seek to ensure t hat humans can co-exist with marine mammals with minimal conflict.

keywords     depredation, marine mammals, fisheries, fish farms, acoustic deterrence, harbor seal, harbor porpoise

abstract
1. Optimal foraging models applied to breath-holding divers predict that diving predators should optimize the time spent foraging at the bottom of dives depending on prey encounter rate, distance to prey patch (depth) and physiological constraints. 2. We tested this hypothesis on a free-ranging diving marine predator, the Antarctic fur seal Arctocephalus gazella, equipped with accelerometers or Hall sensors (n=11) that recorded mouth-opening events, a proxy for prey capture attempts and thus feeding events. Over the 5896 dives analyzed (>15m depth), the mean number of mouth-opening events per dive was 1.21 ą 1.69 (mean ą sd). Overall, 82% of mouth-openings occurred at the bottom of dives. 3. As predicted, fur seals increased their inferred foraging time at the bottom of dives with increasing patch distance (depth), irrespective of the number of mouth-openings. 4. For dives shallower than 55m, the mean bottom duration of dives without mouth-openings was shorter than for dives with mouth-opening events. However, this difference was only due to the occurrence of V-shaped dives with short bottom durations (0 or 1s). When removing those V-shaped dives, bottom duration was not related to the presence of mouth openings anymore. Thus, the decision to abandon foraging is likely related to other information about prey availability than prey capture attempts (i.e. sensory cues) that seals collect during the descent phase. We did not observe V-shaped dives for dives deeper than 55m, threshold beyond which the mean dive duration exceeded the apparent aerobic dive limit. For dives deeper than 55m seals kept on foraging at bottom irrespective of the number of mouth-openings performed. 5. Most dives occurred at shallower depths (30-55m) than the 60m depth of highest foraging efficiency (i.e. of greatest number of mouth-opening events per dive). This is likely related to physiological constraints during deeper dives. 6. We suggest that foraging decisions are more complex than predicted by current theory and highlight the importance of the information collected by the predator during the descent as well as its physiological constraints. Ultimately, this will help establishing reliable predictive foraging models for marine predators based on diving patterns only.

keywords     aerobic diving limit, diving behaviour, foraging strategies, foraging depth, Antarctic fur seals

abstract
Previous research has presented contradictory evidence on the ability of overall dynamic body acceleration (ODBA) to predict oxygen consumption (sV̇O2) in air-breathing diving vertebrates. We investigated a potential source of these discrepancies by partitioning the ODBA: sV̇O2 relationship over 3 phases of the dive cycle (transiting to and from depth, bottom time, and post-dive surface interval). Trained Steller sea lions (Eumetopias jubatus) executed 4 types of dives to 40 m (single dives, long-duration dive bouts of 4-6 dives, short-duration dive bouts of 10 or 12 dives, and transit dives with minimal bottom duration). Partitioning single dives by dive phase showed differing patterns in the ODBA: sV̇O2 relationship among dive phases, but no significant linear relationships were observed. The proportion of the dive cycle spent transiting to and from the surface was a significant predictive factor in the ODBA: sV̇O2 relationship, while bottom duration or post-dive surface interval had no effect. ODBA only predicted sV̇O2 for dives when the proportion of time spent transiting was small. The apparent inability of ODBA to reliably predict sV̇O2 reflects differences in the inherent relationships between ODBA and sV̇O2 during different phases of the dive. These results support the growing body of evidence that ODBA on its own is not a reliable field predictor of energy expenditure at the level of the single dive or dive bout in air-breathing diving vertebrates likely because ODBA (a physical measure) cannot account for physiological changes in sV̇O2 that occur during the different phases of a dive cycle.

keywords     diving behaviour, metabolic rate, ODBA, dive phase, pinniped

abstract
Dive characteristics and dive shape are often used to infer foraging success in pinnipeds. However, these inferences have not been directly validated in the field with video, and it remains unclear if this method can be applied to benthic foraging animals. This study assessed the ability of dive characteristics from time-depth recorders (TDR) to predict attempted prey capture events (APC) that were directly observed on animal-borne video in Australian fur seals (Arctocephalus pusillus doriferus, n=11). The most parsimonious model predicting the probability of a dive with ≥1 APC on video included only descent rate as a predictor variable. The majority (94%) of the 389 total APC were successful, and the majority of the dives (68%) contained at least one successful APC. The best model predicting these successful dives included descent rate as a predictor. Comparisons of the TDR model predictions to video yielded a maximum accuracy of 77.5% in classifying dives as either APC or non-APC or 77.1% in classifying dives as successful verses unsuccessful. Foraging intensity, measured as either total APC per dive or total successful APC per dive, was best predicted by bottom duration and ascent rate. The accuracy in predicting total APC per dive varied based on the number of APC per dive with maximum accuracy occurring at 1 APC for both total (54%) and only successful APC (52%). Results from this study linking verified foraging dives to dive characteristics potentially opens the door to decades of historical TDR datasets across several otariid species.

keywords     Crittercam, Foraging behaviour, Animal-borne video, Dive profile analysis

abstract
Forces due to propulsion should approximate forces due to hydrodynamic drag for animals horizontally swimming at a constant speed with negligible buoyancy forces. Propulsive forces should also correlate with energy expenditures associated with locomotion預n important cost of foraging. As such, biologging tags containing accelerometers are being used to generate proxies for animal energy expenditures despite being unable to distinguish rotational movements from linear movements. However, recent miniaturizations of gyroscopes offer the possibility of resolving this shortcoming and obtaining better estimates of body accelerations of swimming animals. We derived accelerations using gyroscope data for swimming Steller sea lions (Eumetopias jubatus), and determined how well the measured accelerations correlated with actual swimming speeds and with theoretical drag. We also compared dive averaged dynamic body acceleration estimates that incorporate gyroscope data, with the widely used Overa ll Dynamic Body Acceleration (ODBA) metric, which does not use gyroscope data. Four Steller sea lions equipped with biologging tags were trained to swim alongside a boat cruising at steady speeds in the range of 4 to 10 kph. At each speed, and for each dive, we computed a measure called Gyro-Informed Dynamic Acceleration (GIDA) using a method incorporating gyroscope data with accelerometer data. We derived a new metric輸veraged Propulsive Body Acceleration (APBA), which is the average gain in speed per flipper stroke divided by mean stroke cycle duration. Our results show that the gyro-based measure (APBA) is a better predictor of speed than ODBA. We also found that APBA can estimate average thrust production during a single stroke-glide cycle, and can be used to estimate energy expended during swimming. The gyroscope-derived methods we describe should be generally applicable in swimming animals where propulsive accelerations can be clearly identified in the signal預nd they should also prove useful for dead-reckoning and improving estimates of energy expenditures from locomotion.

keywords     biologging, ODBA, accelerometer, gyroscope, swimming, speed, energy expenditure, drag, stroke

abstract
We reconstructed the foraging tracks of lactating northern fur seals (Callorhinus ursinus) from two eastern Bering Sea islands (St. Paul Island and Bogoslof Island) using linear interpolation between GPS locations recorded at a maximum of four times per hour and compared it to tri-axial accelerometer and magnetometer data collected at 16 Hz to reconstruct pseudotracks between the GPS fixes. The high-resolution data revealed distances swum per foraging trip were much greater than the distances calculated using linearly interpolated GPS tracks (1.5 times further for St. Paul fur seals and 1.9 times further for Bogoslof fur seals). First passage time metrics calculated from the high resolution data revealed that the optimal scale at which the seals searched for prey was 500 m (radius of circle searched) for fur seals from St. Paul Island that went off-shelf, and 50 m for fur seals from Bogoslof Island and surprisingly, 50 m for fur seals from St. Paul that foraged on-s helf. These area-restricted search scales were significantly smaller than those calculated from GPS data alone (12 km for St. Paul and 6 km for Bogoslof) indicating that higher resolution movement data can reveal novel information about foraging behaviors that have important ecological implications.

keywords     foraging ecology, biologging, northern fur seal, Callorhinus ursinus, marine mammal, Bering Sea, magnetometer, accelerometer, spatial analysis, area restricted search

abstract
We tagged 82 lactating northern fur seals (Callorhinus ursinus) with tri-axial accelerometers and magnetometers on two eastern Bering Sea islands (Bogoslof and St. Paul) with contrasting population trajectories. Using depth data, accelerometer data and spectral analysis we classified time spent diving (30%), resting (~7%), shaking and grooming their pelage (9%), swimming in the prone position (~10%) and two types of previously undocumented rolling behavior (29%), with the remaining time (~15%) unspecified. The reason for the extensive rolling behavior is not known. We ground-truthed the accelerometry signals for shaking and grooming and rolling behaviors—and identified the acceleration signal for porpoising—by filming tagged northern fur seals in captivity. Speeds from GPS interpolated data indicated that animals traveled fastest while in the prone position, suggesting that this behavior is indicative of destination-based swimming. Very little difference was found in the percentages of time spent in the categorical behaviors with respect to breeding islands (Bogoslof or St. Paul Island), forager type (cathemeral or nocturnal), and the region where the animals foraged (primarily on-shelf <200m, or off-shelf > 200m). The lack of significant differences between islands, regions and forager type may indicate that behaviors summarized over a trip are somewhat hardwired even though foraging trip length and when and where animals dive are known to vary with island, forager type and region.

keywords     seals, accelerometers, animal behavior, foraging, biological locomotion, sine wave, fur seal

abstract
Seasonal changes in daily energy expenditure (DEE) and its key underlying components (costs of resting metabolic rate (RMR), thermoregulation, activity, and growth) were measured to determine seasonal energy requirements, bioenergetic priorities, and potential times of year when unpredicted episodes of nutritional stress would have their greatest effect on female northern fur seals (Callorhinus ursinus L., 1758). The DEE of 6 captive juvenile female fur seals averaged 527.8 Ä… 65.7 kJ kg-1 d-1 (Ä… SD) and fluctuated seasonally (lower during summer and winter, and up to 20% greater in spring and fall). RMR also changed significantly with season, and was higher in the fall (potentially due to moulting or anticipated migratory activity). However, changes in RMR did not follow the same seasonal trend as those of DEE. The largest component of DEE was RMR (~ 80% on average), followed by the cost of activity (which may have driven some of the seasonal variations in DEE). In contrast, the energetic costs associated with growth and thermoregulation appeared negligible within the scope of overall energy expenditures. Elevated innate costs of RMR and higher growth rates in the fall and summer, respectively, suggest that inadequate nutrition could comparatively have greater negative effects on female fur seals during these seasons

keywords     northern fur seal, Callorhinus ursinus, daily energy expenditure,resting metabolic rate, activity, growth, thermoregulation

abstract
Air-breathing divers, such as marine mammals, should adjust their diving behaviours in relation to the depth and density of their prey to minimize the energetic costs and maximize the benefits of foraging. However, there is little experimental data to test these predictions or to develop models to predict the responses of marine mammals to changes in prey availability. The objectives of my study were to 1) determine how changes in prey availability affect dive behaviour and foraging efficiency in Steller sea lions (Eumetopias jubatus) and 2) develop models with data from free-diving captive Steller sea lions to estimate foraging costs in wild animals and evaluate energetic trade-offs between different foraging strategies. I measured the diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on simulated prey patches of high- or low-densities at 10 m and 40 m. I also measured diving metabolic rates of sea lions performing 4 controlled dive types that allowed me to estimate the separate costs of different dive components (i.e., surface time, bottom time, and transiting to and from depth). I found that animals diving on prey patches with low prey density altered their dive behaviours and spent proportionally less time actively foraging, which ultimately decreased their foraging efficiency. I also found that making single, longer dives were less energetically costly than making multiple shorter dives in a bout, but that the sea lions replenished oxygen stores more efficiently when making a bout of dives. Finally, I determined the metabolic cost of transiting to and from depth (20.5Ä…13.0 ml O2 min-1 kg-1) was greater than the cost of foraging during the bottom portion of a dive (13.5Ä…4.1 ml O2 min-1 kg-1). With these values, I generated a predictive equation to estimate the diving costs of free-ranging animals. Overall, my results indicate that Steller sea lions do alter their dive behaviour in relation to prey availability and that different foraging strategies have different energetic costs. These results can be used to understand how changes in prey availability affect the overall energy balance and health of Steller sea lions.

keywords     Steller sea lion, foraging energetics, diving physiology

abstract
Breath-hold divers should adjust their dive behaviors to maximize the benefits and minimize the costs of foraging on prey patches of different densities at different depths. However, few studies have quantified how animals respond to changes in prey availability (depth and density), and how this affects their foraging efficiency. We tested the effects of changes in prey availability on the foraging behavior and efficiency of Steller sea lions (Eumetopias jubatus) by measuring diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on controlled prey patches of different densities at different depths. Sea lions completed bouts of 5 consecutive dives on high- or low-density prey patches at two depths (10m and 40m). We found that the rate of energy expenditure did not change under any of the imposed foraging conditions (meanąSD: 0.22ą0.02 kJ min−1 kg−1), but that the proportion of time spent consuming prey increased with prey patch density due to changes in diving patterns. At both depths, sea lions spent a greater proportion of the dive bout foraging on prey patches with high prey density, which led to high rates of energy gain (4.3 ą 0.96 kJ min−1 kg−1) and high foraging efficiency (cost:benefit was 1:20). In contrast, the sea lions spent a smaller proportion of their dive bout actively feeding on prey patches with low prey density, and consequently had a lower energetic gain (0.91 ą 0.29 kJ min−1 kg−1) and foraging efficiency (1:4). The 5-fold differences in foraging efficiency between the two types of prey patches were greater than the 3-fold differences that we expected based on differences in food availability. Our results suggest that sea lions faced with reduced prey availability forage less efficiently and therefore would have greater difficulty obtaining their daily energy requirements.

keywords     Dive behavior, Diving energetics, Foraging efficiency, Optimal foraging, Steller sea lion

abstract
A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus) in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estima te the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.

keywords     Eumetopias jubatus, walleye pollock, Pacific cod, Atka mackerel, accessibility, prey distribution, CPUE, linear mixed-effects models

abstract
Efficient extraction of energy from the environment is key to the survival and reproductive success of wild animals. Understanding the ratio of energy gained to energy spent of different foraging strategies (i.e., foraging efficiency) can shed light on how animals cope with environmental changes and how it affects population trajectories. I investigated how female foraging strategies during the breeding season impact the foraging efficiencies and reproductive successes of two fur seal species—one declining (NFS–northern fur seals, St. Paul Island, Alaska) and one increasing (AFS–Antarctic fur seals, Kerguelen Island, Southern Ocean). I also sought to develop new accelerometry-based methods to easily determine fine-scale energy expenditure at sea (VeDBA and flipper stroke metrics). Twenty lactating females of each species were captured and equipped with biologging tags to record GPS locations, depth and tri-axial acceleration. Energy expenditure for each foraging trip was measured using the doubly-labeled water method, and energy gained while foraging was determined from 1) diet composition (scat hard-parts and DNA) and blood stable isotope ratios; and 2) numbers of prey capture attempts (from head acceleration). Maternal investment in pups was determined from pup growth rates or from energy content of milk samples. Results showed acceleration metrics were only accurate at predicting energy expended by fur seals when time-activity budgets were taken into account (i.e., time spent performing different types of activity). Foraging strategies of AFS females resulted in efficiencies of ~3.4, with more efficient females producing bigger pups at weaning that had greater chances of survival. NFS females employed two foraging strategies with very different efficiencies (~1.4 vs. ~3.0) that were associated with different foraging habitats and diet qualities. However, NFS with the more efficient strategy (3.0) undertook longer foraging trips than the oth er NFS ( 1.4) or AFS (3.4), and thus fed their pups ~20% less frequently. As a consequence, the declining NFS (unlike the increasing AFS) had to compromise between the rate of energy acquisition and the pup feeding frequency. Such reductions in energy intake and time allocated to nursing pups can ultimately lower juvenile survival, and may explain the population decline of NFS in Alaska.

keywords     northern fur seals, St. Paul Island, Alaska, Antarctic fur seals, Kerguelen Island, foraging efficiency, foraging strategies, breeding season, reproductive successes, biologging, accelerometry, VeDBA, flipper stroke, doubly-labeled water, diet compos

abstract
Northern fur seals (Callorhinus ursinus) breeding on the Pribilof Islands, Alaska have declined dramatically over the past 40 years. Effective conservation of northern fur seals depends on understanding the foraging behaviour of adult females whose foraging success is linked to pup survival. We determined the foraging behaviour for 11 tagged lactating female northern seals from the Pribilof Islands using a state-space modelling approach with an autoregressive movement model. To interpret at-sea behaviour in the context of oceanic habitat, we matched high-resolution reconstructed tracks spatially and temporally to a set of environmental covariates that included: commercial groundfish catch, sea surface temperature, primary productivity, wind speed, depth and time of day. We used a Bayesian hierarchical framework to implement a multinomial regression model to link behaviour to environmental covariates; and account for the mismatch of scale between fur seal behaviour and the environmental variables by incorporating an error-in-covariates approach into the hierarchical model. The Bayesian framework allowed us to build a single model to synthesize the information from all the northern fur seal foraging tracks and the available information about the underlying environmental conditions. Application of the approach indicated that the behavioural states for the northern fur seal were significantly related to the Alaska commercial groundfish catch, particularly walleye pollock (Gadus chalogramma).

keywords     northern fur seal, Bayesian hierarchical model, error-in-covariates, diel pattern, juvenile walleye pollock

abstract
Fin whales are acoustically active year-round, particularly during the winter breeding season when males produce song as a reproductive display. Little is known about movement patterns and population structure of the fin whale (Balaenoptera physalus) in the North Pacific. I used passive acoustic data recorded using bottom-mounted autonomous recording instruments to answer questions about the winter distribution, behaviour and population structure of fin whales in a high-latitude area of the eastern North Pacific Ocean. I found that fin whales are present in British Columbia (BC) waters throughout the winter, and their acoustic behaviour suggests that they are engaging in reproductive and possibly feeding behaviour. The presence of these individuals indicates that not all fin whales migrate south in the winter to low-latitude breeding grounds. I found that the majority of fin whales recorded in BC sang a doublet song with alternating ~13 s and ~17 s intervals between alternating classic and backbeat notes (song Type 2). At the most northerly recording site, and the two offshore sites, I found a few instances of a previously described doublet song type that has longer internote intervals (song Type 1). This suggests that two spatially segregated populations of fin whales are using BC waters, with the population producing song Type 2 being more coastal. Through a literature search, I found evidence of song Type 2 occurring from northern BC to Oregon. Song Type 1 has been documented off Southern California, the Bering Sea and the central North Pacific. My results are consistent with evidence showing that two genetically distinct fin whale populations occur in the eastern North Pacific, and that the population that produces song Type 2 is more closely related to the Southern Hemisphere subspecies of fin whale, than to the other population of fin whales in the North Pacific. My results show that BC waters are important for fin whales year-round, rather than just during the summer feeding season―and that the fin whales in BC likely belong to two distinct populations (one of which may belong to the Southern Hemisphere subspecies) and may require separate plans for their conservation and management.

keywords     passive acoustics, fin whale, distribution, behavior, population structure, reproduction, feeding, song

abstract
Biologgers incorporating triaxial magnetometers and accelerometers can record animal movements at infra-second frequencies. Such data allow the Dead-Reckoned (DR) path of an animal to be reconstructed at high-resolution. However, poor measures of speed,undocumented movements caused by ocean currents, confounding between movement and gravitational acceleration and measurement error in the sensors, limits the accuracy and precision of DR paths. The conventional method for calculating DR paths attempts to reduce random errors and systematic biases using GPS observations without rigorous statistical justification or quantification of uncertainty in the derived swimming paths. Methods: We developed a Bayesian Melding (BM) approach to characterize uncertainty and correct for bias of DR paths. Our method used a Brownian Bridge process to combine the fine-resolution (but seriously biased) DR path and the sparse (but precise and accurate) GPS measurements in a statistically rigorous way. We also exploited the properties of underlying processes and some approximations to the likelihood to dramatically reduce the computational burden of handling large, high-resolution data sets. We implemented this approach in an R package "BayesianAnimalTracker", and applied it to biologging data obtained from northern fur seals (Callorhinus ursinus) foraging in the Bering Sea. We also tested the accuracy of our method using cross-validation analysis and compared it to the conventional bias correction of DR and linear interpolation between GPS observations (connecting two consecutive GPS observations by a straight line). Results: Our BM approach yielded accurate, high-resolution estimated paths with uncertainty quantified as credible intervals. Cross-validation analysis demonstrated the greater prediction accuracy of the BM method to reconstruct movements versus the conventional and linear interpolation methods. Moreover, the credible intervals covered the true path points albeit with probabilities somewhat higher than 95%. The GPS corrected high-resolution path also revealed that the total distance traveled by the northern fur seals we tracked was 40% - 50% further than that calculated by linear interpolation of the GPS observations.

keywords     Biologging; Dead-Reckoning; High-resolution animal tracking; Bayesian melding; energy expenditure; Global Positioning System; uncertainty statement; Brownian Bridge

abstract
Our knowledge of cetacean distributions is impeded by large data-gaps worldwide, particularly at tropical latitudes. This study aims to (1) understannd generic relationships between cetaceans and their habitats in a range of tropical waters, and (2) extrapolate cetacean densities in a circumtropical belt extending far beyond surveyed regions. Aerial surveys were conducted over three regions in the tropical Atlantic (132,000 km2), Indian (1.4 million km2) and Pacific (1.4 million km2)oceans. Three cetacean guilds were studied (Delphininae, Globicephalinae andsperm and beaked whales). For each guild, a generalized additive model was submitted using sightings recorded in all three regions and 14 candidate environmental predictors. Cetacean densities were tentatively extrapolated over a circumtropical belt, excluding waters where environmental characteristics departed from those encountered in the surveyed regions. Each cetacean guild exhibited a relationship with the primary production and depth of the minimum dissolved oxygen concentration. Delphininae also showed a relationship with the dominant phytoplankton group. The prediction envelopes were primarily constrained by water temperature. Circumtropical extrapolations of Delphininae and Globicephalinae were contrasted between ocean basins, with high densities predicted in the equatorial waters of the three ocean basins. The predicted densities of sperm and beaked whales were lower and more uniform across the circumtropical belt than for the other two guilds. Our modelling approach represents a good analytical solution to predicting cetacean population densities in poorly documented tropical waters. Future data collection should concentrate on areas where environmental characteristics were not encountered in our survey regions and where the predicted densities were the most uncertain. By highlighting cetacean hotspots far beyond waters under national jurisdiction, this study can provide guidance for the delimitation of Ecologically and Biologically Significant Marine Areas.

keywords     Cetaceans, circumtropical, conservation biogeography, density, extrapolation, generalized additive models, pelagic waters

abstract
Feeding performance studies can address questions relevant to feeding ecology and evolution. Our current understanding of feeding mechanisms for aquatic mammals is poor. Therefore, we characterized the feeding kinematics and performance of five Steller sea lions (Eumetopias jubatus) and six northern fur seals (Callorhinus ursinus). We tested the hypotheses that both species use suction as their primary feeding mode, and that rapid jaw opening was related to suction generation. Steller sea lions used suction as their primary feeding mode, but also used a biting feeding mode. In contrast, northern fur seals only used a biting feeding mode. Kinematic profiles of Steller sea lions were all indicative of suction feeding (i.e. a small gape, small gape angle, large depression of the hyolingual apparatus and lip pursing). However, jaw opening as measured by gape angle opening velocity (GAOV) was relatively slow in Steller sea lions. In contrast to Steller sea lions, the GAOV of northern fur seals was extremely fast, but their kinematic profiles indicated a biting feeding mode (i.e. northern fur seals exhibited a greater gape, a greater gape angle and minimal depression of the hyolingual apparatus compared with Steller sea lions). Steller sea lions produced both subambient and suprambient pressures at 45 kPa. In contrast, northern fur seals produced no detectable pressure measurements. Steller sea lions have a broader feeding repertoire than northern fur seals, which likely enables them to feed on a greater variety of prey, in more diverse habitats. Based on the basal phylogenetic position of northern fur seals, craniodental morphological data of the Callorhinus lineage, and the performance data provided in this study, we suggest that northern fur seals may be exhibiting their ancestral feeding mode.

keywords     Otariidae, Callorhinus ursinus, Eumetopias jubatus,suction, biting, fossil pinnipeds

abstract
The accuracy of estimates of cetacean density from line-transect survey data depends in large part on how visible the target species is to the observer. Behavioural data (i.e. surface and dive times) from government- and industry-funded aerial observation programs (1980-2000) were used to calculate availability correction factors needed to estimate the number of bowhead whales (Balaena mysticetus) from aerial survey sighting data. Correction factors were calculated for bowheads exposed and not exposed to seismic operations. Travelling non-calf whales were found to be less likely to be available for detection than other whales, and their availability further declined in the presence of seismic operations. Non-calves were also less available to observers during autumn when exposed to seismic operations than when not exposed, regardless of activity (travelling or otherwise). Such differences in availability appear to reflect behavioural responses to the sound of seismi cooperations that alters the surfacing and diving patterns of bowhead whales. Localised abundance estimated from aerial surveys may range from 3% to as much as 63% higher in areas ensonified by seismic operations if correction factors are applied to account for differences in availability associated with the presence of seismic operations, compared to abundance estimates derived from assessments that only account for changes in availability of undisturbed whales. These results provide the first empirical estimates of availability for bowhead whales exposed to seismic operations and highlight the implications of not correcting for disturbance-related availability in density assessments in the vicinity of seismic operations.

abstract
Past foraging success of diving air-breathing vertebrates can adversely affect future foraging capabilities and costs through changes in circulation or increased metabolic costs associated with digestion that are incompatible with efficient diving. This study tested the physiological interaction between digestion and diving by comparing the cost of diving in fasted and pre-fed trained Steller sea lions foraging under controlled conditions in the open ocean. Pre-dive and post-dive surface metabolism and diving metabolic rate were all higher in the pre-fed animals than the fasted animals, indicating an effect of digestion on metabolism. However, the sea lions displayed a significant reduction in the apparent additive effect of digestion during diving. The increase in rate of oxygen consumption associated with digestion was reduced by 54% during diving compared to the increase observed in pre-dive metabolism. This truncation of the additional cost of digestion rapidly disappeared following cessation of diving. The results suggest that Steller sea lions diving to depth demonstrate a partial deferment of digestion while actively foraging and that the classically held view that digestion and diving are incompatible processes may be much more variable and adaptable to specific diving conditions and behaviors than previously thought.

abstract
Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomics approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with diet restriction regulation in terrestrial mammals. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

keywords     Genomics, Expression profile, q-PCR, Diet, restriction, Biomarker, Monitoring

abstract
Changes in marine species abundance can impact ecosystems’ stability and sustainability of fisheries. In the eastern Atlantic Ocean, harbour seals (Phoca vitulina) are top predator occupying highest trophic level in coastal marine food webs. Although, the overall European population decline, harbour seals have increased dramatically since the 1990Â’s at the southern limit of their European distribution along the French coast of the English Channel. However, little is known about the feeding habits of the expanding peripheral populations limiting the assessment of the role and the impact of this predator in these coastal ecosystems. Here, we investigated the sex-specific diet of harbour seals during summer in the Bay of Somme, the largest colony in the English Channel. We collected 91 faecal samples from haul-out sites mainly used by harbour seal but also by few grey seals. Molecular methods have been used to discard grey seal samples and differentiate gender. Collectively, the 86 faecal samples of harbour seals contained the remains of 3327 prey belonging to at least 13 fish species, and represented ~109 kg of consumed fish (of which 85% were soles and plaices). Most of the fish consumed were juvenile and small flatfish (Buglossidium luteum, Microchirus variegatus, Solea vulgaris, Pegusa lascaris, Pleuronectes platessa and Platichthys flesus). Hard-part identification further showed a similar diet between the sexes in terms of primary prey consumed, but a greater diversity of preys in the male diet. The dependence of harbour seals on flatfish has not been reported elsewhere and has significant implications for the sustainability of the important flatfish nursery in the Bay of Somme. Consumption estimation and ecosystem modelling are now required to provide robust assessment of the effect of harbour seal predation on population dynamics of the flatfish nursery, on ecosystem of the Bay of Biscay at- large, and finally on interactions with fisheries.

abstract
Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically inert once formed. Additionally, vibrissae are grown in utero, potentially offering indirect inference on maternal diet. However, diet reconstruction using isotopic techniques requires a priori knowledge of trophic enrichment factors (TEFs), which can vary relative to diet quality and among animal species. In this study, we provide new TEF estimates for (1) maternal relative to pup vibrissae during both gestation and nursing and (2) adult vibrissae relative to a complex diet. Further, we refine vibrissa−milk TEFs based on an additional 76 animals with an age distribution ranging from 1 to 20 mo. Mother−pup vibrissae TEF values during gestation and nursing were near zero for δ13C and averaged 0.8 and 1.6‰, respectively, for δ15N. In contrast, vibrissa− fish/invertebrate TEFs averaged 3.3 (± 0.3 SD) and 3.7‰ (±0.3) for lipid-free δ13C and δ15N, respectively. Average lipid-free δ13C and δ15N vibrissa−milk TEFs were 2.5 (±0.9) and 1.8‰ (±0.8), respectively, and did not differ among metapopulations. Empirically determined TEFs are critical for accurate retrospective diet modeling, particularly for evaluating the hypothesis of nutritional deficiency contributing to the lack of Steller sea lion population recovery in some regions of Alaska.

abstract
Harbour seals have long been perceived to compete with fisheries for economically valuable fish resources in the Pacific Northwest, but assessing the amounts of fish consumed by seals requires estimates of harbour seal diets. Unfortunately, traditional diet analysis techniques cannot provide the necessary information to estimate the species, life stage, and biomass of key prey (e.g. salmonids) consumed by seals. I therefore developed a new harbour seal diet analysis methodology, using scat DNA metabarcoding and prey hard-part analysis to create refined estimates of salmon in harbour seal diet. I also sought to understand the quantitative potential of DNA metabarcoding diet analysis (i.e. the relationship between prey biomass proportions and DNA sequence percentages produced by high-throughput amplicon sequencing of seal scat DNA). Analysis of faecal samples (scats) from captive harbour seals fed a constant diet indicated that a wide range of factors influence the nu mbers of prey sequences resulting from scat amplicon sequencing. These biases ranged from preferential amplification of certain prey species DNA, to sequence quality filtering—in addition to interactions between the various biases. I was able to apply correction factors derived from tissue mixtures of the species fed to captive seals that improved prey biomass estimates from DNA, and found that the lipid content of prey fish species perfectly predicted the magnitude of bias resulting from differential prey digestion. My results suggest that highly accurate pinniped prey biomass estimates can be attained by applying two stages of corrections to prey DNA sequence counts. However applying these corrections to the scats of wild seals is challenging, and requires a complete prey tissue mix library to create species-specific correction factors for all prey. While I established an approach that could be applied to wild seals, a thorough statistical evaluation and follow-up feeding studies are need ed to determine if the additional effort is justified for population level diet estimates. Lastly, I developed a decision tree approach for merging salmon DNA and hardparts data from seal scats to determine the species and life stages of salmon consumed by seals in the Strait of Georgia, British Columbia.

keywords     harbour seals, diet analysis, salmonids, scat, DNA metabarcoding, prey hard-part analysis, high-throughput amplicon sequencing, Strait of Georgia, British Columbia

abstract
We compared eight dietary indices used to describe the diet of Steller sea lions (Eumetopias jubatus (Schreber, 1776)) from 2001-2004 in Frederick Sound, Southeast Alaska. Remains (n=9 666 items) from 59+ species categories were identified from 1 693 fecal samples (scats) from 14 collection periods. The most frequently occurring prey were walleye pollock (Theragra chalcogramma (Pallas, 1814), 95%), Pacific herring (Clupea harengus (Cuvier and Valenciennes, 1847), 30%), Pacific hake (Merluccius productus (Ayres, 1855), 29%), and arrowtooth flounder (Atheresthes stomias (Jordan and Gilbert 1880), 21%). These species, along with salmon (Oncorhynchus spp.) and skate (Raja spp.), accounted for 80-90% of the reconstructed biomass and energy contribution, with pollock contributing 37-60%. Overall, 80% of fish were 14-42cm long and mainly pelagic, though 40% of scats contained benthic-associated prey. Steller sea lions switched from adult pollock to strong cohorts of juvenile pollock, and took advantage of spawning concentrations of salmon in autumn and herring in late-spring and summer, as well as a climate-driven increase in hake availability. Observed temporal and site differences in diet confirm the need for robust long-term scat sampling protocols. All major indices similarly tracked key temporal changes, despite differences in occurrence and biomass-energy based diet estimates linked to prey size and energy density effects and the application of correction factors.

keywords     Diet, scat, biomass reconstruction, hard remains, otoliths, Steller sea lion, dietary index

abstract
This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

keywords     Arctocephalus pusillus doriferus, accelerometer, prey capture success, foraging behavior, foraging success, pinniped

abstract
We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption (sVO2) in freely diving Steller sea lions ( Eumetopias jubatus/) while resting at the surface and diving. The trained sea lions executed three dive types―single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout葉o depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from sVO2. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type was analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11%, and standard error of the estimated AMR was 5-32%. Overall, the extensive range of dive behaviours and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

keywords     Steller sea lion, oxygen consumption, overall dynamic body acceleration, activity, oxygen depletion, diving physiology

abstract
The core objective of efforts to understand and mitigate the effects of whale-watching has been to ensure the survival of populations. The first rigorous studies in the 1980s simply demonstrated that short-term behavioural responses existed. Managers, both in the private sector (whale-watch operators) and public sector responded with simple guidelines. Later studies showed some practices elicited stronger responses than others, and managers again responded with more effective guidelines to preclude activities that elicited strong evasive responses from killer whales. Recent work has shown that these guidelines are insufficient to prevent effects likely to be directly related to fitness (e.g. a reduction in foraging activity and increases in energy expenditure). As managers contemplate how to respond to such results, models such as ours can be constructed to address how short-term effects might relate to population dynamics, and whether data support a correlation between the quantity of exposure and shifts in population growth and decline. As better parameter estimates become available to inform these simple bioenergetics and population dynamics models, they should provide sufficient accuracy and precision to determine whether the effects of vessel traffic are sufficient to reduce the probability that the populations will survive in the long term (i.e. do they exceed potential biological removal (PBR)), or do the cumulative effects of whale watching and other human activities put the population in jeopardy of imminent extinction? The resident killer whales of the northeast Pacific represent an exceedingly data-rich case study of behavior and population biology, but they also represent an interesting study in management. The degree to which management is or is not precautionary determines how much evidence of population-level effects is needed before management actions are imposed. And as some of the science that has been done on this population is applied to other cetaceans, it is important to spell out another lesson learned— namely, that it is essential to specify quantitative management objectives that identify how much of an effect managers are willing to tolerate (limits of acceptable change, PBR and uncertainty:. Otherwise, the science can and will continue without serving any practical purpose as long as the whales persist.

abstract
Recent European environmental policies argue for the development of indicators of the ecological status of ecosystems that are easy to implement and powerful enough to detect changes quickly. For instance, some indicators that are currently proposed for monitoring foodweb structure and functioning are based on the size of organisms, using size as a proxy for trophic level. However, these indicators do not necessarily accurately reflect the underlying trophic structure and dynamics to follow. Ecological tracers (i.e. chemical parameters measured in consumer tissues to infer the trophic ecology of organisms) may serve as complementary indicators of trophic level, and may also help distinguish different populations of a species when more commonly used methods (e.g. genetic, age determination) present their own limitations. Here, we analysed the potential of muscle δ13C and δ15N values and of muscle mercury (Hg) concentrations to depict size-related trophic ha bits of different fish species. We expected that intra- and interspecific variation in these ecological tracers could be helpful in refining currently proposed indicators of marine ecosystems, and also help in discriminating management unitsfor some species. Four fish species were selected for their economical and/or ecological importance in the Bay of Biscay (Northeast Atlantic): whiting Merlangius merlangus, European hake Merluccius merluccius, Atlantic horse mackerel Trachurus trachurus and anglerfish Lophius piscatorius. Muscle δ13C and δ15N values segregated the species and enabled us to discriminate species-specific feeding strategies with increasing size of individuals. Fish body size was not always linearly correlated with δ15N or trophic level. In contrast, Hg concentrations and size-related Hg patterns were more similar from species to species. Interestingly, muscle δ15N values together with Hg concentrations segregated the two putative stocks of Europe an hake within the Bay of Biscay. Hence, we propose the combined use of ecological tracers as a promising method for accurately assigning a consumer to a trophic guild, investigating Hg trophodynamics in foodwebs, and helping discriminate distinct ecological populations within a species when defining management units.

abstract
Seasonal changes in the daily energy expenditure (DEE) of captive northern fur seals (Callorhinus ursinus) and key components of their energy budget (cost of resting metabolism, thermoregulation, activity and growth) were examined to elucidate potential reasons for the species’ population decline in the wild. The average DEE of 6 females was 527.8 ± 65.7 kJ kg-1 d-1 and fluctuated seasonally (~20% greater in the fall than in the winter). Resting metabolism also changed significantly with season, and was higher in the fall (potentially due to molting or as preparation for migratory activity). While resting metabolism was the largest component of the DEE (~80% on average), it did not follow the same seasonal trend as DEE, and therefore was not the source of the seasonal variation in DEE. Cost of activity was the second major component of DEE and may explain the observed seasonal variations. Energetic costs associated with thermoregulation appeared to be negligible. The northern fur seals were thermally neutral in all seasons for all water temperatures tested (2 °C – 18 °C), except during the summer when immersed in 2 °C water. Comparing this broad thermal neutral zone to the average sea surface temperatures encountered by fur seals in the wild during annual migrations indicates that fur seals can likely exploit a large geographic area without added thermal metabolic costs. While the direct energetic costs of growth appeared to be negligible compared to DEE, the higher growth rates in the summer and elevated resting metabolism in the fall suggests that inadequate nutrition could have greater negative effects during these seasons. Two alternative proxies for measuring energy expenditure were tested and calibrated against respirometry for potential application to wild individuals. The doubly labeled water (DLW) method over-estimated DEE by 13.1 ± 16.5% compared to respirometry. In comparison, accelerometry over-estimated DEE, using fine time scale intervals of 60 and 15 min, by an average of 5.4 ± 29.3% and 13.8 ± 39.5%, respectively. Importantly, seasonal effects (and time of day for accelerometry) must be accounted for when estimating energy expenditure from measures of DLW and acceleration in free-swimming northern fur seals.

keywords     Northern Fur Seal, Daily Energy Expenditure, Thermoregulation, Activity, Resting Metabolic Rate, Growth, Doubly Labelled Water, Accelerometry, Respirometry

abstract
Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75 to 3.5 yr old) in ambient air and controlled water temperatures of 2, 10, and 18 °C. Rates of oxygen consumption in ambient air (1 – 18 °C) were not related to environmental temperature except below 2.5 °C (winter only). However, metabolism was significantly higher during the fall seasonal trials (Sept – Oct) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperat ures tested (2 – 18 °C) except during the summer when metabolic rates were higher in the 2 °C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.

abstract
Estimates of energy expenditure for free-ranging animals are essential to answering a range of fundamental questions in animal biology, but are challenging to obtain and difficult to validate. We simultaneously employed three methods to measure the energy expenditure of 6 captive female northern fur seals (Callorhinus ursinus) during 5-day trials across 4 seasons: respirometry (oxygen consumption), doubly labeled water (DLW), and accelerometry. The DLW method estimated that the fur seals expended 13.1 ? 16.5% more energy than indicated by the more direct measures of oxygen consumption. Accelerometry failed to predict the average mass specific rate of oxygen consumption (VË™ O2DEE) within the individual seasons over entire 5- day trials. However, on a finer time scale (15 or 60 min) and adjusted for time of day, accelerometry estimated energy expenditure within an average difference of 5.4 ? 29.3% (60 min intervals) and 13.8 ? 39.5% (15 min intervals) of respirometry measured values. Our findings suggest that accelerometers have the potential to be more effective than the DLW method for measuring energy expenditure of free-ranging animals. However, rates of oxygen consumption varied with season, independent of overall activity. Seasonal effects (and time of day for accelerometry) must therefore be accounted for when estimating energy expenditure from measures of DLW and acceleration of free-swimming northern fur seals. Such corrections required for estimating energy expenditures in northern fur seals have implications for using accelerometers and DLW to estimate the energy expenditure of other species.

keywords     accelerometry, Callorhinus ursinus, daily energy expenditure, doubly labeled water, northern fur seal, respirometry

abstract
We examined structural properties of the marine mammal respiratory system, and tested Scholander's hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised in an aquatic facility. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance.

abstract
The diving ability of marine mammals is limited by body oxygen stores (TBO) and rates of oxygen depletion (diving metabolic rate; DMR), which can be expressed as the calculated aerobic dive limit (cADL). Diving ability must also be influenced by CO₂ production and control of ventilation. I investigated the factors that limit the diving ability of Steller sea lions (Eumetopias jubatus), including the effect of nutritional stress on the cADL. Specifically, I 1) determined the cADL of Steller sea lions by measuring TBO and DMR, 2) determined whether nutritional stress alters the cADL and 3) examined the post-dive elimination of CO₂, and the sensitivity of Steller sea lions to hypercapnia (high inspired CO₂). TBO was estimated from measured blood oxygen stores and body composition―and metabolic rate, breathing frequency and dive behaviour were recorded prior to and during a period of nutritional stress where animals lost ~10% of their mass. Animals breathed ambient, hypercapnic or hypoxic (low O₂) air to experimentally alter pCO₂ levels and decrease rates of CO₂ elimination and O₂ consumption. I found that the TBO (35.9 ml O₂ kg-¹) and cADL (3.0 minutes) in actively diving Steller sea lions were lower than previously reported for other species of sea lions and fur seals. I also found a significant increase in mass-specific DMR and blood volume (resulting in higher TBO) in nutritionally stressed animals that resulted in a longer cADL. Hypercapnia was found to significantly affect ventilation, but had no effect on dive behaviour―and elimination of CO₂ between dives took longer than replenishing O₂ stores. Overall, nutritional stress and hypercapnic conditions did not directly limit the diving ability of the Steller sea lions, but had an indirect effect on foraging efficiency by increasing the time they spent on the surface between dives. Accumulation of CO₂ over several dives in a foraging bout also appeared to reduce foraging efficiency, which likely ultimately limits the time a sea lion spends in apnea and therefore overall foraging duration and net energy intake.

abstract
Marine mammal foraging behaviour inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.

abstract
Marine mammal foraging behavior inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.

keywords     Steller sea lion, blood volume, nutritional stress, diving metabolism, oxygen stores, dive behavior

abstract
With the recent advances in electrical engineering, devices attached to free-ranging marine mammals today can collect oceanographic data in remarkable high spatial-temporal resolution. However, those data cannot be fully utilized without a matching high-resolution and accurate path of the animal, which is currently missing in this field. In this paper, we develop a Bayesian melding approach based on a Brownian Bridge process to combine the fine-resolution but seriously biased Dead-Reckoned path and the precise but sparse GPS measurements, which results in an accurate and high-resolution estimated path together with credible bands as quantified uncertainty statements. We also exploit the properties of underlying processes and some approximations to the likelihood to dramatically reduce the computational burden of handling those big high resolution data sets.

keywords     Dead reckoning, swimming path, northern fur seal, Bayesian melding, Brownian Bridge

abstract
A number of hypotheses have been proposed to explain the most recent decline (1977-2012) of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. We examined hypotheses about fisheries competition, environmental change, predation, anthropogenic effects, and disease using observations of modern Aleut and archaeological, ethnohistoric, and ethnographic data from the western Gulf of Alaska and Aleutian Islands. These data indicate that Steller sea lion numbers have declined and recovered repeatedly over the past 4,500 years and were last at critically low numbers during the 1870s-1930s. Steller sea lions appear to have been more abundant during the cool periods—and lower during the warmer periods. Observations by local peoples, explorers, early government surveyors, and biologists since the late 1800s suggest that low populations of Steller sea lions have been associated with high populations of Gadidae fishes (Pacific cod – Gadus macrocephalus and walleye pollock – Theragra chalcogramma), and are consistent with the ocean climate hypothesis to explain the decline of sea lions. They suggest that removals by people and killer whales (Orcinus orca) did not cause the sea lion declines, but could have compounded the magnitude of the decline as sea lion numbers approached low densities. Archaeological, anthropological and ethnohistorical analyses demonstrate that fluctuations have occurred in the North Pacific over hundreds to thousands of years, and provide context for understanding the changes that occur today and the changes that will continue to occur in the future.

abstract
Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn were investigated in the liver and kidney of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin. Differences were observed in the bioaccumulation of the above elements between the five species. The differences are probably related to biological factors such as age and sex and/or to ecological factors specific to each species such as feeding habits or bioavailability of the various elements. However, no significant relationship was observed between element accumulation and sex. Pilot whale and striped dolphin showed the highest concentrations of renal Cd and the highest concentrations of hepatic Hg and Se, while bottlenose dolphin showed the highest concentrations of Hg in kidneys. An analysis of inter-elemental relationships showed strong positive correla tions be tween Hg and Se in the five species, however most individuals have Hg:Se molar ratio less than 1:1 indicating an excess of Se compare to Hg. This result, probably reflect the high proportion of young animals in the sample available for this study and/or that these animals had a good health status. We also observed a positive correlation in striped dolphins between Cd and Cu and between Cd and Zn in kidneys. In addition, comparing with other studies world-wide, the element concentrations (Hg and Cd) found in Iberian toothed whales indicate that these populations are not specially threatened by Hg and Cd exposure in the area.

keywords     Trace elements; Bioaccumulation; Toothed whales; Northwest Iberian Peninsula

abstract
Concentrations and patterns of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the blubber of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin, were investigated. The study revealed that differences in PCB and PBDE concentrations among the species are highly dependent on age and sex but also on ecological factors such as trophic level, prey type and habitat. Of the five species studied, bottlenose dolphin and harbour porpoise showed the greatest concentrations of PCBs. Both species exceed the toxic threshold of 17 μg g− 1 lipid weight (PCB Aroclor equivalent) for health effects on marine mammals, for 100% and 75% of the individuals tested, respectively. Overall, the PCB and PBDE levels observed in the NWIP toothed whales were of the same order of magnitude or lower than those reported by previ ous studies in areas of the NE Atlantic. However, they are often higher than those for toothed whales from the southern Atlantic and Pacific Ocean.

keywords     PCBs; PBDEs; Bioaccumulation; Patterns; Toothed whales; Northwest Iberian Peninsula

abstract
We report two opportunistic and unusual observations of white-beaked dolphins (Lagenorhynchus albirostris) in the Canadian Arctic that are outside the known range of this species. Sightings occurred off the south-east coast of Baffin Island (Nunavut, Canada) in Frobisher Bay (September 2004) and Cumberland Sound (August 2013). Despite dedicated, multi-year marine mammal surveys in the region (boat-based and aerial), white-beaked dolphins have not previously been reported in the eastern Davis Strait. Our sightings suggest that white-beaked dolphins may infrequently inhabit coastal waters off south-eastern Baffin Island, and furthermore, that their habitat use may correspond with recent changes in prey distribution and availability.

keywords     distribution; western North Atlantic; white-beaked dolphins

abstract
Assessments of distribution and abundance are a common means of gauging impacts of anthropogenic activities on wildlife. However, the influence of behavioural responses on estimated numbers and distributions of animals is rarely considered within this context. I used behavioural data collected in the Beaufort Sea from 1980-2000 to investigate the effects of seismic operations on the distribution and abundance of bowhead whales (Balaena mysticetus). Bowhead whales are known to vary their dive and surface-respiration behaviour when exposed to seismic survey operations, although it is unknown whether these changes in behaviour differ by season, reproductive status and activity (feeding, socializing and travelling). Overall, I found that changes in behaviour of whales exposed to seismic operations were context dependent (i.e., they were contingent on the whale’s circumstance and activity). I then investigated the effects of these behaviour changes on the sightability of whales to aerial observers conducting line-transect surveys. I calculated and compared sightability correction factors specific to whales exposed and not exposed to seismic operations and found that whales in all circumstances were less available for detection when exposed to seismic sounds. In particular, non-calves were the least available to observers during autumn when exposed to seismic activities, regardless of activity state. I used line-transect distance sampling and spatial modeling methods to generate corrected density estimates for bowhead whales in an area of the southern Alaskan Beaufort Sea ensonified by seismic operations between late August and early October 2008 to investigate the extent to which density analyses were affected by changes in whale availability. The resultant density surface models revealed a wide-spread nearshore distribution of whales within the ensonified area with some spatial segregation related to activity state. Density estimates that accounted for variations in whale behavior due to seismic operations were also 25–64 % higher than previous estimates. Collectively, these findings suggest that seismic activities may not have displaced bowhead whales as previously thought, but altered their dive behaviours instead ,making them less visible for counting. My research demonstrates the importance of accounting for behavioural reactions when assessing impacts of seismic operations on distributions and abundances of whales.

keywords     bowhead whale, behaviour, seismic testing, distribution, disturbance, abundance, Beaufort Sea, Arctic

abstract
Unexpected shortages of food may affect wildlife differently depending on the time of year it occurs. We imposed 48-hr fasts on six female northern fur seals (Callorhinus ursinus; ages 6 ? 24 months) to identify times of year when they might be particularly sensitive to interruptions in food supply. We monitored changes in their resting metabolic rates and their metabolic response to thermal challenges, and also examined potential bioenergetic causes for seasonal differences in body mass loss. Pre-fast metabolism of the fur seals while in ambient air or submerged in 4 ?C water was higher during summer (Jun-Sep) than winter (Nov-Mar), and submergence did not significantly increase metabolism indicating a lack of additional thermoregulatory costs. There was no evidence of metabolic depression following the fasting periods, nor did metabolism increase during the post-fast thermal challenge, suggesting that mass loss did not negatively impact thermoregulatory capacity. However, the fur seals lost mass at greater rates while fasting during the summer months when metabolism is normally high to facilitate faster growth rates (which would ordinarily have been supported by higher food intake levels). Our findings suggest that summer is a more critical time of year than winter for young northern fur seals to obtain adequate nutrition.

abstract
The thermoregulatory abilities of northern fur seals (Callorhinus ursinus) during their first two years in the frigid waters of the North Pacific Ocean may limit their geographic distribution and alter the costs for exploiting different species of prey. We determined the thermoneutral zone of 6 young northern fur seals by measuring their metabolism in ambient air and controlled water temperatures (0-12 °C) from ages 8 to 24 mo. We found that the ambient air temperatures within our study (overall 1.5-23.9 °C) did not affect resting metabolic rates. Calculated lower critical temperatures in water varied between 3.9 and 8.0 °C, while an upper critical temperature in water was only discernible during a single set of trials. These thermal responses provide insight into the possible physiological constraints on foraging ecology in young northern fur seals, as well as the potential energetic consequences of ocean climate change and altered prey distributions.

keywords     Northern fur seal, Callorhinus ursinus, thermoregulation, metabolism, bioenergetics

abstract
Understanding ‘Why a prey is a prey for a given predator?’ can be facilitated through trait-based approaches that identify linkages between prey and predator morphological and ecological characteristics and highlight key functions involved in prey selection.' Enhanced understanding of the functional relationships between predators and their prey is now essential to go beyond the traditional taxonomic framework of dietary studies and to improve our knowledge of ecosystem functioning for wildlife conservation and management. We test the relevance of a three-matrix approach in foraging ecology among a marine mammal community in the northeast Atlantic to identify the key functional traits shaping prey selection processes regardless of the taxonomy of both the predators and prey. Our study reveals that prey found in the diet of marine mammals possess functional traits which are directly and significantly linked to predator characteristics, allowing the establishment of a functional typology of marine mammal–prey relationships. We found prey selection of marine mammals was primarily shaped by physiological and morphological traits of both predators and prey, confirming that energetic costs of foraging strategies and muscular performance are major drivers of prey selection in marine mammals. We demonstrate that trait-based approaches can provide a new definition of the resource needs of predators. This framework can be used to anticipate bottom-up effects on marine predator population dynamics and to identify predators which are sensitive to the loss of key prey functional traits when prey availability is reduced.

abstract
Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus) that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m) under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC) tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (,12–26% subcutaneous fat). Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag) showed that swim speed was best predicted by two variables, drag and dive phase (AIC=-139). Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.

abstract
Ecologists are increasingly interested in quantifying consumer diets based on food DNA in dietary samples and high-throughput sequencing of marker genes. It is tempting to assume that food DNA sequence proportions recovered from diet samples are representative of consumer's diet proportions, despite the fact that captive feeding studies do not support that assumption. Here, we examine the idea of sequencing control materials of known composition along with dietary samples in order to correct for technical biases introduced during amplicon sequencing, and biological biases such as variable gene copy number. Using the Ion Torrent PGM©, we sequenced prey DNA amplified from scats of captive harbour seals (Phoca vitulina) fed a constant diet including three fish species in known proportions. Alongside, we sequenced a prey tissue mix matching the seals’ diet to generate Tissue Correction Factors (TCFs). TCFs improved the diet estimates (based on sequence proportions) for all species and reduced the average estimate error from 28 ± 15% (uncorrected), to 14 ± 9% (TCF corrected). The experimental design also allowed us to infer the magnitude of prey-specific digestion biases and calculate Digestion Correction Factors (DCFs). The DCFs were compared to possible proxies for differential digestion (e.g., fish% protein,% lipid,% moisture) revealing a strong relationship between the DCFs and percent lipid of the fish prey, suggesting prey-specific corrections based on lipid content would produce accurate diet estimates in this study system. These findings demonstrate the value of parallel sequencing of food tissue mixtures in diet studies and offer new directions for future research in quantitative DNA diet analysis.

keywords     next-generation sequencing; diet analysis; pinniped; correction factors

abstract
Many eyes and ears keep watch over marine mammals in the Strait of Georgia. They range from the dedicated individuals who mobilize to help a stranded cetacean or care for a sick seal or porpoise, to the mariners and whale watchers who are often the first to notice unusual events or the changes in numbers and distribution. For them and many others, marine mammals are fascinating creatures and important indicators of the health of the Strait of Georgia. The eleven species of seals, sea lions, porpoises, dolphins and baleen whales that inhabit the Strait of Georgia constitute an incredible diversity of abundant marine life to be living on the doorstep of one of the largest concentrations of people in North America. It represents one of the most accessible assemblages of marine mammals in the world for people to see and observe, and is a testament to the richness and bio-diversity of the Strait of Georgia that often goes unseen and unrecognized by many who walk its shores.

abstract
Foragers with narrow dietary niches often exhibit specialized hunting behaviours that improve their efficiency for capturing preferred prey, but can leave them vulnerable if the abundance of this prey declines. I examined the specificity of foraging behaviour by a highly selective predator, the northern resident killer whale (Orcinus orca), which specializes on Chinook salmon (Oncorhynchus tshawytscha). Northern residents are undoubtedly well adapted to capture Chinook, however, their hunting tactics have never been described due to the challenges of quantifying underwater behaviour. To address this research gap, I deployed archival tags (DTAGs) on 32 killer whales to measure their acoustic and kinematic behaviour during foraging dives. Reconstructed 3-dimensional tag tracks indicated that foraging and non-foraging dives were kinematically distinct. While engaged in hunting behaviour, whales dove deeper, remained submerged longer, swam faster, increased their dive path tort uosity, and rolled their bodies more than during other activities. Maximum foraging dive depths reflected both the deeper vertical distribution of Chinook (compared to other salmonids), as well as the tendency of these fish to evade predation by diving steeply. Inferences from whale movements further revealed that salmon engaged in other anti-predation strategies, including increasing swim speeds and evasive manoeuvring. DTAG records also provided the first definitive link between echolocation and prey captures by resident killer whales, who displayed significantly higher clicking rates and spent proportionally more time echolocating prior to capturing a fish than they did afterward. Rapid ‘buzz’ click sequences were often produced before fish captures, which is consistent with their hypothesized function of close-range prey targeting. Furthermore, prey handling ‘crunches’ were usually detected following kills and, with buzzes, provide possible acoustic proxies for capture attempts and successes that could be used to estimate foraging efficiency. My thesis determined that northern resident killer whales possess specialized foraging behaviours for targeting Chinook salmon. The specificity of these behaviours may make the whales less effective at capturing other types of fish. If northern residents have limited flexibility to modify their foraging behaviour to successfully exploit other prey types when Chinook availability is reduced, prey capture efficiency (and thus per capita energy intake) could decline.

keywords     prey capture, northern resident, DTAG, salmon

abstract
We propose a method to model the physiological link between somatic survival and reproductive output that reduces the number of parameters that need to be estimated by models designed to determine combinations of birth and death rates that produce historic counts of animal populations. We applied our Reproduction and Somatic Survival Linked (RSSL) method to the population counts of three species of North Pacific pinnipeds (harbor seals, Phoca vitulina richardii (Gray, 1864); northern fur seals, Callorhinus ursinus (L., 1758); and Steller sea lions, Eumetopias jubatus (Schreber, 1776))—and found our model outperformed traditional models when fitting vital rates to common types of limited datasets, such as those from counts of pups and adults. However, our model did not perform as well when these basic counts of animals were augmented with additional observations of ratios of juveniles to total non-pups. In this case, the failure of the ratios to improve model performance may indicate that the relationship between survival and reproduction is redefined or disassociated as populations change over time or that the ratio of juveniles to total non-pups is not a meaningful index of vital rates. Overall, our RSSL models show advantages to linking survival and reproduction within models to estimate the vital rates of pinnipeds and other species that have limited time-series of counts.

keywords     Callorhinus ursinus, Eumetopias jubatus, harbor seal, model parameterization, northern fur seal, Phoca vitulina richardii, pinniped, population dynamics, reproduction, senescence, survival, vital rates

abstract
Spatial coherence between predators and prey has rarely been observed in pelagic marine ecosystems. We used measures of the environment, prey abundance, prey quality, and prey distribution to explain the observed distributions of three cooccurring predator species breeding on islands in the southeastern Bering Sea: black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia), and northern fur seals (Callorhinus ursinus). Predictions of statistical models were tested using movement patterns obtained from satellite-tracked individual animals. With the most commonly used measures to quantify prey distributions - areal biomass, density, and numerical abundance - we were unable to find a spatial relationship between predators and their prey. We instead found that habitat use by all three predators was predicted most strongly by prey patch characteristics such as depth and local density within spatial aggregations. Additional prey patch characteristics and physic al habitat also contributed significantly to characterizing predator patterns. Our results indicate that the smallscale prey patch characteristics are critical to how predators perceive the quality of their food supply and the mechanisms they use to exploit it, regardless of time of day, sampling year, or source colony. The three focal predator species had different constraints and employed different foraging strategies – a shallow diver that makes trips of moderate distance (kittiwakes), a deep diver that makes trip of short distances (murres), and a deep diver that makes extensive trips (fur seals). However, all three were similarly linked by patchiness of prey rather than by the distribution of overall biomass. This supports the hypothesis that patchiness may be critical for understanding predator-prey relationships in pelagic marine systems more generally.

abstract
Marine prey often occur in hierarchical mosaics whereby small, high-density patches are nested inside of larger, lower density aggregations. We tested the extent to which the foraging behavior of a marine predator (northern fur seal Callorhinus ursinus) could be explained by the hierarchical patch structure of a dominant prey species (juvenile walleye pollock Theragra chalcogramma) in the eastern Bering Sea. Comparing the movements of satellite-tracked fur seals with ship-based acoustic surveys of prey revealed that fur seals did not randomly search for prey, but instead showed deviations in the distribution of step-lengths (distances between their foraging patches) corresponding to the distances between aggregations of prey. Scales of prey distribution varied between Bering Sea shelf and deep-water slope habitats, while spatial scale distributions of fur seals showed corresponding changes, indicating that their search strategies were not innate patterns decoupled from the environment. Fur seals tended to avoid the smallest prey patches in both shelf and slope habitats. They also avoided prey patches that were separated by large distances. Fur seals responded to several levels of prey patchiness simultaneously, resulting in strong correlations between predator and prey over the entire range of aggregation scales observed in juvenile pollock. Our results indicate that, despite having a varied diet, fur seal foraging paths were defined by juvenile pollock aggregations. The presence of hierarchical, scale-dependent aggregation in both predator and prey provides new insights into fur seal behavior and a means to predict the dynamics of their interactions with prey.

keywords     Patchiness, Spatial scale, Predator–prey, Foraging behavior, Hierarchical, Northern fur seal, Juvenile walleye pollock

abstract
Dietary information is critical for assessing the population status of seals, sea lions and walruses—and is determined for most species of pinnipeds using non-invasive methods. However, diets of walruses continue to be described from the stomach contents of dead individuals. Our goal was to assess whether DNA could be extracted from the faeces of Pacific walruses (O. rosmarus divergens) collected at haulout sites, and whether potential prey species or taxa could be amplified from that DNA. We extracted DNA from 70 faecal samples collected from ice pans in the Bering Sea during the spring of 2008 and 2009 (with between 4.6 and 308.9 ng/µl of DNA in every sample). We also extracted DNA from 12 potential prey species or taxa collected by bottom grabs in 2009 to identify positive controls for primers, and to test the ability of previously published taxon-specific and species-specific primers to correctly identify the prey using conventional PCR. We tested primers that successfu lly amplified DNA from the tissue of at least one potential prey species or taxon on all 70 walrus faecal samples. We found that two sets of primers successfully amplified many of the potential prey species or taxa using DNA from their tissue, and that one of these primer sets produced positive amplification in 4 of the 70 faecal samples. The band size that was produced for prey organisms and in the faecal samples was consistent with expectations, although prey identities were not verified with sequencing. Our pilot study demonstrates that DNA can be successfully extracted and amplified from walrus faeces, providing a stepping stone towards describing the diets of walruses from faecal DNA.

abstract
A goal of many environmental DNA barcoding studies is to infer quantitative information about relative abundances of different taxa based on sequence read proportions generated by high-throughput sequencing. However, potential biases associated with this approach are only beginning to be examined. We sequenced DNA amplified from faeces (scats) of captive harbour seals (Phoca vitulina) to investigate whether sequence counts could be used to quantify the seals’ diet. Seals were fed fish in fixed proportions, a chordate- specific mitochondrial 16S marker was amplified from scat DNA and amplicons sequenced using an Ion Torrent PGM™. For a given set of bioinformatic parameters, there was generally low variability between scat samples in proportions of prey species sequences recovered. However, proportions varied substantially depending on sequencing direction, level of quality filtering (due to differences in sequence quality between species) and minimum read length considered. Short primer tags used to identify individual samples also influenced species proportions. In addition, there were complex interactions between factors; for example, the effect of quality filtering was influenced by the primer tag and sequencing direction. Resequencing of a subset of samples revealed some, but not all, biases were consistent between runs. Less stringent data filtering (based on quality scores or read length) generally produced more consistent proportional data, but overall proportions of sequences were very different than dietary mass proportions, indicating additional technical or biological biases are present. Our findings highlight that quantitative interpretations of sequence proportions generated via high- throughput sequencing will require careful experimental design and thoughtful data analysis.

keywords     DNA barcoding, Ion Torrent, metabarcoding, next-generation sequencing, pinniped diet

abstract
Three Steller sea lions (Eumetopias jubatus), trained to dive voluntarily to depths ranging from 10 to 50 m, were used to determine whether the relationship between activity and metabolic rate during a diving interval (MRDI, dive + surface interval) was affected by fasting (9-days) during the breeding season (spring through summer). We subsequently used the relationship between activity and MRDI to partition the metabolic costs between underwater breath-holding activity and surface breathing activities. We estimated activity from Overall Dynamic Body Acceleration (ODBA) measured using a 3-axis accelerometer, and measured MRDI using flow-through respirometry. The relationship between ODBA-based activity and MRDI was not affected by fasting period, suggesting ODBA can be used to predict energy expenditure regardless of nutritional state in the spring and summer. However, the relationship between ODBA and dive metabolic rate differs from the relationship between ODBA and the s urface metabolic rate before diving (MRSp). Partitioning MRDI into the metabolic cost of remaining at the surface (MRs) versus swimming underwater (MRUS) suggests that the metabolic cost of diving for Steller sea lions is approximately 29% lower than when breathing at the surface. ODBA appears to be a reasonable proxy to estimate metabolic rate in marine mammals, but more detailed behavioral data may be required to accurately apply the method in the field.

abstract
Management plans for North Atlantic right whales Eubalaena glacialis focus on preventing mortality from ship strikes and fishing gear entanglement. However, recovery may also be limited because individuals are under nutritional stress. We quantified the food requirements of North Atlantic right whales by age, sex and reproductive state and compared their predicted needs with field estimates of prey consumption to assess whether any demographic group of right whales might be nutritionally stressed. Energy requirements were estimated using a bioenergetics model that accounted for uncertainty in energy inputs and outputs. Consumption was estimated with prey samples taken near feeding whales in Cape Cod Bay (n = 28 net collections) and the Bay of Fundy (n = 19 optical plankton recordings). We found that calves required the least energy (~1767 MJ d-1) and that lactating females required the most (~4120 MJ d-1). Juveniles required considerably more energy than adult males and non-reproductive females. Our estimates of energy requirements for juveniles (~1906 MJ d-1), adult males (~1793 MJ d-1), and non-reproductive females (~2104 MJ d-1) compared favorably with estimates of actual consumption in Cape Cod Bay and the Bay of Fundy (i.e. they differed by ≤15%), suggesting that our model was reliable. However, lactating females appear to have obtained considerably less than their predicted energy requirements in both habitats. These findings suggest that lactating females may be experiencing an energy deficit, which may affect reproductive rates and slow population recovery. Nutritional stress may thus be limiting the recovery of North Atlantic right whales.

keywords     Bioenergetic model, Eubalaena glacialis, nutritional stress, energetic consumption, energetic requirements

abstract
The diving capacity of marine mammals is typically defined by the aerobic dive limit ^(ADL) which, in lieu of direct measurements, can be calculated ^(cADL) from total body oxygen stores (TBO) and diving metabolic rate ^(DMR). To estimate cADL, we measured blood oxygen stores, and combined this with diving oxygen consumption rates ^(VO(2) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O⁽²⁾ stores by comparing blood O⁽²⁾ stores of our diving animals to non-diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O⁽²⁾ stores between the diving and non-diving groups. Estimated TBO ^{(35.9 ml O(2)} kg^(-1) )was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O⁽²⁾ min^(-1)) and was signific antly shorter than the average 4.4 min dives our study animals performed when making single long dives-but was similar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO⁽²⁾ and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought.

abstract
Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15–30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000–2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either ‘West’ or ‘East’). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2–5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two ‘mixing zone’ rookeries. We documented breeding bulls that traveled 6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.

keywords     branding, resights, distribution, migration, movements, colonization

abstract
This study aims to assess niche segregation among the five main toothed whales that frequent the NW Iberian Peninsula waters: the common dolphin, the harbour porpoise, the bottlenose dolphin, the striped dolphin and the long-finned pilot whale. We used cadmium (Cd) and stable isotope ratios (d 13C and d15N) as ecological tracers to assess degree of segregation in diet/trophic level and in foraging habitat, over various time-scales. d13C values highlighted different habitats, while Cd concentrations highlighted feeding differences between oceanic and neritic species. Moreover, d15N values suggest different trophic levels of prey targeted within oceanic and neritic species. Hence, results revealed long-term ecological segregation among five toothed whales that coexist in the NWIP and demonstrated the ability of ecological tracers to discriminate ecological niches among closely related species.

abstract
The relationships between fine-scale oceanographic features, prey aggregations, and the foraging behavior of top predators are poorly understood. We investigated whether foraging patterns of lactating northern fur seals (Callorhinus ursinus) from two breeding colonies located in different oceanographic domains of the eastern Bering Sea (St. Paul Island shelf; Bogoslof Island˜oceanic) were a function of submesoscale oceanographic features. We tested this by tracking 87 lactating fur seals instrumented with bio-logging tags (44 St. Paul Island, 43 Bogoslof Island) during JulyˆSeptember, 2009. We identified probable foraging hotspots using first-passage time analysis and statistically linked individual areas of high-use to fine-scale oceanographic features using mixed-effects Cox-proportional hazard models. We found no overlap in foraging areas used by fur seals from the two islands, but a difference in the duration of their foraging trips˜trips from St. Paul Island were twice as long (7.9 d average) and covered 3-times the distance (600 km average) compared to trips from Bogoslof Island. St. Paul fur seals also foraged at twice the scale (mean radius = 12 km) of Bogoslof fur seals (6 km), which suggests that prey were more diffuse near St. Paul Island than prey near Bogoslof Island. Comparing first passage times with oceanographic covariates revealed that foraging hotspots were linked to thermocline depth and occurred near submesoscale surface fronts (eddies and filaments). St. Paul fur seals that mixed epipelagic (night) and benthic (day) dives primarily foraged on-shelf in areas with deeper thermoclines that may have concentrated prey closer to the ocean floor, while strictly epipelagic (night) foragers tended to use waters with shallower thermoclines that may have aggregated prey closer to the surface. Fur seals from Bogoslof Island foraged almost exclusively over the Bering Sea basin and appeared to hunt intensively along submesoscale fronts that may have converged prey within narrow bands near the surface. Bogoslof fur seals also foraged closer to their island which was surrounded by strong surface fronts, while fur seals from St. Paul Island traveled4100 km and extended some trips off-shelf to the basin to forage at similar oceanographic features. The relative distribution and accessibility of prey-concentrating oceano- graphic features can account for the observed inter-island foraging patterns, which may in turn have population level consequences for the two fur seal colonies.

keywords     Habitat selection, First-passage time, Submesoscale features, Finite-size Lyapunov exponent,Cox proportional hazard model, Alaska, Eastern Bering Sea

abstract
Oceanographic data collected by marine vertebrates are increasingly being used in biological and physical studies under the assumption that data recorded by free-ranging animals are comparable to those from traditional vertical sampling. We tested this premise by comparing the water temperatures measured during a 2009 oceanographic cruise with those measured during 82 foraging trips by instrumented northern fur seals (Callorhinus ursinus) in the eastern Bering Sea. The animal-borne data loggers were equipped with a fast-response temperature sensor and recorded 6,492 vertical profiles to depths ≥ 50 m during long distance (up to 600 km) foraging trips. Concurrent sampling during the oceanographic cruise collected 247 CTD casts in the same 5-week period. Average temperature differences between ship casts and seal dives (0.60 ± 0.61 °C), when the two were within 1 day and 10 km of each other (n = 32 stations), were comparable to mean differences between adjacent 10 km ship casts (0.46 ± 0.44 °C). Isosurfaces were evaluated at region wide scales at depths of 1 m and 50 m while the entire upper 100 m of the water column was analyzed at finer-scales in highly sampled areas. Similar trends were noted in the temperature fields produced by ships or seals despite the differences in sampling frequency and distribution. However, the fur seal dataset was of higher temporal and spatial resolution and was thereby able to visualize finer-detail with less error than ship-derived data, particularly in dynamic areas. Integrating the ship and seal datasets provided temperature maps with an unprecedented combination of resolution and coverage allowing fine-scale processes on-shelf and over the basin to be described simultaneously. Fur seals (n = 65 trips) also collected 4,700 additional profiles post ship cruise which allowed ≥1 °C warming of the upper 100 m to be documented through mid-September, including regions where ship sampling has traditionally been sparse. Our data show that hydrographic information collected by wide-ranging, diving animals such as fur seals can contribute physical data comparable to, or exceeding those, of traditional sampling methods at regional or finer scales when the questions of interest coincide with the ecology of the species.

abstract
The Pacific white-sided dolphin (Lagenorhynchus obliquidens) is one of the most abundant apex predators in the North Pacific Ocean, but little is known about how much food they consume and whether their food requirements vary seasonally. We attempted to address these two issues using the feeding records of five Pacific white-sided dolphins housed at the Vancouver Aquarium. These individuals consumed an average of 7.9 kg ± 0.35 (± SE) of fish and squid per day (~11,000 kcal day-1), which equated to ~7% of their body mass and an annual mean intake of 2,880 kg ± 131.8 (± SE) per dolphin (N = 5). Patterns of food consumption and seasonal changes were assessed using long-term feeding records (1977 to 2001) from a single adult female, and were found to be highest in terms of biomass and calories in late December, and about 15% less in late May and early June. Seasonal pool temperatures (range 6.5 to 21.5 C) were inversely related to food intake and accounted for part of the variation, suggesting that seasonal cues other than temperature triggered the changes in food consumption. Amounts of prey consumed by Pacific white-sided dolphins are undoubtedly higher in the wild than in captivity due to relative differences in their respective behaviors in the two environments. However, relative seasonal changes in energy requirements are likely to be independent of living conditions and have implications for estimating the energy requirements of Pacific white-sided dolphins in the wild.

abstract
Apex predators such as Pacific white-sided dolphins (Lagenorhynchus obliquidens) have the potential to impact prey populations and to be affected by changes in prey abundance. As an abundant predator that ranges widely across the North Pacific Ocean, their interactions with prey populations may have conservation implications. We estimated the energy required by individual Pacific white-sided dolphins using a bioenergetic model that accounted for different age classes and reproductive stages (calf, juvenile, adult, pregnant and lactating). Monte Carlo simulations incorporating variability in model parameters (body mass, growth rate, costs of gestation and lactation, metabolic rate, cost of activity, and assimilation efficiencies) were used to predict ranges in energetic requirements. Mean (±SD) total energy requirements in MJ day-1 were 40.3 ± 6.2 for calves, 70.8 ± 8.2 for juveniles, 69.0 ± 3.6 for adults, 70.3 ± 3.6 for pregnant females, and 98.4 ± 20.0 for lactating femal es. Estimates of energy requirements were most sensitive to uncertainty in values used for resting metabolic rates and energetic costs of activity. Estimated mass-specific energy requirements in MJ kg-1 day-1 were elevated in calves (1.55 ± 0.23), juveniles (0.97 ± 0.11) and lactating females (1.01 ± 0.21) when compared with non-reproductive adults and pregnant females (~0.71 ± 0.04). Based on a high-energy density diet, an average sized dolphin (78 kg) would consume approximately 12.5 - 15.8 kg of fish or 15-20% of its body weight per day. These high energetic requirements may indicate a reliance of dolphins on energy rich prey, which has implications for fisheries management and conservation of marine mammals.

abstract
Like many marine mammals, Pacific white-sided dolphins (Lagenorhynchus obliquidens) consume prey that change seasonally in numbers, distribution, and energy density. However, it is not known whether these ecological factors are associated with underlying seasonal changes in energy requirements. We investigated these potential seasonal shifts in physiology by measuring resting metabolic rate (a conserved physiological trait) and recording associated daily food energy intake of three captive adult Pacific white-sided dolphins over 12 consecutive months. Two dolphins that met the criteria for measuring resting metabolism had a mean (± SE) mass-specific rate of 0.31 ± 0.0047 MJ kg-1 day- 1 (~34 MJ day-1), which was higher than that of other species of small cetaceans. Resting metabolic rates of Pacific white-sided dolphins did not vary seasonally and, hence, were not related to observed seasonal changes in water or air temperature, total energy intake, or body mass. Overall, resting metabolism accounted for ~70% of total energy intake. However, total food energy intake changed seasonally and was highest during the fall (October to December). While levels of food intake were not predicted by resting metabolic rate, body mass, or water and air temperatures, the increased intake in the fall resulted in the seasonal increase in body mass exhibited by all three dolphins. Our estimates of resting metabolic rates and relative changes in total energy intake can be used to parameterize bioenergetic models needed to estimate the ecological impacts and energetic requirements of Pacific white-sided dolphins in the wild, which will have conservation implications.

keywords     energetics, oxygen consumption, Pacific white-sided dolphins, season, food intake, metabolic rate

abstract
The surfacing, respiration and diving (SRD) behavior of bowhead whales Balaena mysticetus changes upon exposure to seismic operations. However, it is unknown whether these changes differ by season, reproductive status (calves, mothers, and non-calves), and whale activity (traveling, foraging, or socializing). Such SRD behavioral responses to seismic operations might influence the detectability of whales during aerial surveys. We addressed these questions by applying non-parametric univariate tests and linear mixed models to behavioral data collected by aerial observation of bowheads in the Beaufort Sea from 1980 to 2000. Durations of surfacings decreased upon exposure to seismic operations, especially for traveling or socializing non-calf whales. The mixed models also indicated that dive durations were affected by the presence of seismic operations, but the effects depended on other variables such as season and whale activity. Overall, our results suggest that changes in the behavior exhibited by bowhead whales exposed to seismic operations are context-dependent (i.e. responses to seismic operations depend on both the circumstance and activity of the whale). The level of perceived threat may also be important based on similarities with behavioral changes observed in other air-breathing aquatic foragers facing dangers. We conclude that seismic-induced changes in bowhead SRD behaviors may affect the availability of bowhead whales for visual detection in some circumstances. This in turn means that estimates of abundance and distribution of bowhead whales near seismic surveys should be context-sensitive and incorporate correction factors that account for sound exposure, season, reproductive status, and whale activity.

keywords     Bowhead whale, Behavior, Disturbance, Seismic operations,Beaufort Sea,Aerial surveys, Sightability

abstract
We conducted repeated measurements of rates of oxygen consumption on a mature (~17 yrs) male beluga whale held at the Vancouver Aquarium, and trained to rest quietly at the surface of his holding pool underneath a specially designed floating dome that completely contained the portion of his body above the water line. Each trial lasted ~20 minutes prior to the morning feed, and rates of oxygen consumption were calculated over the last 10 minutes of each trial. The average metabolic rate over 11 trials was 73,050 ± 2290 kJ d-1 (Mean ± S.E.). This translated into approximately 54.48 ± 1.71 kJ kg-1 d-1, which was approximately 1.13 ± .035 times the predicted value for a similarly-sized terrestrial mammal. This was statistically greater than 1.0, but did not approach the much higher values reported for many other small cetacean species.

abstract
In the northeastern Atlantic, adult sea bass (Dicentrarchus labrax) is one of largest fish living on the shelf, and this species has important commercial value. However, pelagic trawl fisheries that target sea bass have negative operational interactions with common dolphins (Delphinus delphis). Our goal was to determine the diet of adult sea bass in the Bay of Biscay from stomachcontent and stable-isotope analyses, and explore the dietary overlap between sea bass and common dolphins. We found that sea bass primarily target small pelagic fish, most notably mackerel (Scomber scombrus), scads (Trachurus spp.), anchovy (Engraulis encrasicolus), and sardine (Sardina pilchardus). These four species also dominated the diets of common dolphins. This overlap in feeding preferences could increase the risk of dolphins being caught by trawl fisheries while feeding among sea bass, and may be an underlying mechanism to explain the high rate of common dolphin bycatch observed in the pelagic trawl fishery for sea bass in the Bay of Biscay. Understanding the foraging ecology and trophic interactions of predator species is an essential step for identifying and resolving management issues in the northeastern Atlantic and other marine ecosystems.

keywords     Chesson’s index, marine top predator, prey selection, SIAR, stable isotope, stomach content

abstract
Energy densities of 670 individual fish from nine different species were measured to evaluate intraspecific variability. Functional groups based on energy density appeared to be sufficiently robust to individual variability to provide a classification of forage fish quality applicable in a variety of ecological fields including ecosystem modelling.

keywords     calorific value, prey quality, ecological grouping, functional ecology

abstract
The core breeding population of northern fur seals (Callorhinus ursinus) in North America has declined significantly since the 1980s on St. Paul Island (one of the Pribilof Islands) while the smaller nearby population at Bogoslof Island (eastern Bering Sea) has increased exponentially. Further south, the population of northern fur seals on San Miguel Island off the coast of Southern California has fluctuated between exponential growth and catastrophic declines associated with re-occurring El Nino events. The goal of my thesis was to asses the physiological status of these three breeding populations of northern fur seals in North America to determine whether nutritional differences could explain the different population trajectories. I collected fecal samples (scats) in July 2009 from these three islands and measured the fecal metabolites of two hormones ˜ a glucocorticoid associated with the stress response, and triiodothyronine (T3), a thyroid hormone associated with metabolic rate. I also assessed feeding conditions using diet and foraging data. I found that sub-adult males and lactating females on St. Paul Island experienced poorer feeding conditions (lower energy content food and longer feeding trips for lactating females) than at Bogoslof Island, but that only the females were nutritionally stressed. I also found that the San Miguel Island population differed physiologically compared to the northern populations in Alaska in terms of stress and nutritional status. The San Miguel fur seals were the most physiologically stressed of the North American fur seal populations (based on elevated levels of glucocorticoid metabolites). However, the stress was most likely related to heat stress and not food (based on low concentrations of T3 metabolites). The available hormone, diet, and foraging data from northern fur seals in North America suggest that lactating females were nutritionally stressed on St. Paul Island and heat stressed on San Miguel Island, and experienced better conditions on Bogoslof Island.

abstract
South American fur seals (Arctocephalus australis) continue to survive in Peru in spite of commercial harvesting, periodic disappearance of prey (i.e., El Niño), and competition with the Peruvian anchoveta fishery. I investigated the ability of the Peruvian population of fur seals to recover from catastrophic declines at two temporal and spatial scales. The first analysis determined intrinsic rate of growth (r) and the potential carrying capacity (K*˜the number of fur seals that could be supported in Peru in the absence of sealing and El Niño) from 1880ˆ2010, and the second used pup counts from 1984ˆ2010 to determine the relationship between prey abundance and the timing of pupping at an important fur seal breeding site in southern Peru. Model results indicated that South American fur seals in Peru have an intrinsic growth rate r of 0.20 and a potential carrying capacity K* of 115,000 seals. Recent counts (2007) show that current population is at 33% of the estimated mean numbers of fur seals alive from 1880-1925. Analysis of 25 years of counts of pups and adult females at the breeding site showed a correlation between anchoveta biomass and mean birth dates (r2 = 0.59, P<0.01) and with the ratio of pups to females (r2 = 0.66, P<0.01) in the upcoming breeding seasons. It also revealed a 2-week shift in the mean birth date that may reflect a change in the age structure of the population. Numbers of pups born tended to be lower in years with low anchoveta biomass, as did recruitment of young females. Monitoring daily numbers of pups born and adult females appears to be a useful means to assess the feeding conditions encountered by South American fur seals in Peru. My study also suggests that South American fur seals are adapted to survive in extremely disturbed environments and have the potential to rapidly recover following population declines. Whether or not they ever again achieve their potential carrying capacity will depend upon protection of breeding rookeries, a continued harvest ban, reduced bycatch, incidental captures and illegal poaching, regulation of anchoveta fishing quotas and good environmental conditions.

keywords     population dynamics, prey abundance, anchoveta, Peru, South American fur seals, pup production

abstract
Humpback whales are common in feeding areas off British Columbia (BC) from spring to fall, and are widely distributed along the coast. Climate change and the increase in population size of North Pacific humpback whales may lead to increased anthropogenic impact and require a better understanding of species-habitat relationships. We investigated the distribution and relative abundance of humpback whales in relation to environmental variables and processes in BC waters using GIS and generalized additive models (GAMs). Six non-systematic cetacean surveys were conducted between 2004 and 2006. Whale encounter rates and environmental variables (oceanographic and remote sensing data) were recorded along transects divided into 4 km segments. A combined 3-year model and individual year models (two surveys each) were fitted with the mgcv R package. Model selection was based primarily on GCV scores. The explained deviance of our models ranged from 39% for the 3-year model to 76% for the 2004 model. Humpback whales were strongly associated with latitude and bathymetric features, including depth, slope and distance to the 100-m isobath. Distance to sea-surface-temperature fronts and salinity (climatology) were also constantly selected by the models. The shapes of smooth functions estimated for variables based on chlorophyll concentration or net primary productivity with different temporal resolutions and time lags were not consistent, even though higher numbers of whales seemed to be associated with higher primary productivity for some models. These and other selected explanatory variables may reflect areas of higher biological productivity that favor top predators. Our study confirms the presence of at least three important regions for humpback whales along the BC coast: south Dixon Entrance, middle and southwestern Hecate Strait, and the area between La Perouse Bank and the southern edge of Juan de Fuca Canyon.

abstract
Management plans for North Atlantic right whales (Eubalaena glacialis) focus on preventing mortality from ship strikes and fishing gear entanglement. However, population recovery may also be limited by nutritional stress. I derived growth curves and quantified the food requirements of North Atlantic right whales by age, sex and reproductive state. I also compared their predicted needs with field estimates of prey consumption to evaluate the model predictions and consider whether different demographic groups of right whales might be nutritionally stressed. Energy requirements were estimated using a bioenergetics model that incorporated uncertainty in energy inputs and outputs. Consumption was estimated with prey samples taken near feeding whales in two critical feeding habitats˜Cape Cod Bay (n=28 net collections) and the Bay of Fundy (n=19 optical plankton counts). Model predictions indicate that mothers invest heavily in their calves, which effectively double in size and attain ~73% of their mother‚s length by weaning at one year of age. Calves gained an average of ~1.7 cm and ~34 kg per day while nursing during this rapid growth phase. Body growth was best described using a two-phased Gompertz model and could not be fit using any of the single continuous growth models commonly used for other mammals. Energetically, calves required the least energy (~1129 MJ/day) and lactating females required the most (~2934 MJ/day). Adult males and non-reproductive females fell in between at ~1140 and ~1217 MJ/day respectively. Estimates of energy requirements for juveniles, adult males, pregnant and non-reproductive emales compared favorably with estimates of actual prey consumption in their winter habitat (i.e., they differed by ≤15%), suggesting that the model was reliable. However, lactating females appear to obtain considerably less (~45%) of their predicted daily energy requirements in Cape Cod Bay, and almost met their needs in the Bay of Fundy (obtaining ~87% of daily requirements). This suggests that lactating females may be experiencing an energy deficit, which may affect reproductive rates and slow population recovery. Nutritional stress may thus be limiting the recovery of North Atlantic right whales.

keywords     North Atlantic right whale, nutritional stress, energetics, prey consumption, growth

abstract
Body growth of North Atlantic right whales (Eubalaena glacialis) was described from measurements of known- age live and dead individuals to gain insights into the nutritional needs and life-history strategies of this endangered species. Body lengths from 154 individuals revealed that calves more than doubled in size and attained three-fourths of asymptotic adult size by the time they had weaned at 12 months. Calves gained on average ~1.7 cm and ~34 kg per day while nursing during this extremely rapid growth phase. Mean predicted lengths and weights were 4.2 m and 1.1 metric tons (mt) at birth, 10.3 m and 13.5 mt at weaning, and 13.6 m and 29.6 mt when fully grown. Growth of right whales was best described using a 2-phased Gompertz growth model and could not be fit using any of the single continuous growth models commonly used for other mammals. Rapid growth during dependency may minimize the risk of predation and maximize calf survival. Rapid calf growth also may maximize development of the mouth and baleen to optimize foraging efficiency of juveniles at the time of weaning, as well as improve reproductive fitness by reducing the age at which sexual maturity is attained. However, transferring the amount of energy needed to support the rapid postnatal growth of North Atlantic right whales may ultimately affect the intervals between pregnancies (.3 years) of mature females.

keywords     Eubalaena glacialis, growth models, length, mass, reproductive costs, right whale

abstract
Service data does not exist for the strength of enclosures for subdermally implanted biotelemetry devices intended for young wild animals. Developing adequate tests especially for implants intended for endangered species is difficult due to the very limited availability of live animals and cadaverous tissue, ethical concerns about using them, and high enclosure costs. In this research, these limitations were overcome by taking a conservative approach to design and testing. Reliability tests were developed and performed to establish the likelihood that a thin subdermally and cranially implanted alumina enclosure would fail due to typical external forces related to diving, fights, and falls over the expected 30-year life time of sea lions. Cyclic fatigue tests indicative of deep dives performed out of tissue and at the 90% reliability level indicated no failure after 70,000 stress cycles at stresses of approximately 15 MPa; dynamic fatigue tests indicated a 5% probability of failure at 250 MPa; and puncture tests indicative of fight bites showed a 5% probability of failure at 1500 N. These values were far outside of what the animals might expect to encounter in real life. On the other hand, the response of the enclosure to impact outside of the tissue was failure at a mean energy level of 6.7 J. Modeling results predict that head impacts due to trampling by fighting sea lion males and falls over 1 m onto a rocky ledge typical of haul out environments would likely fracture an infant‚s head as well as the implant. The device can be implanted under an impact absorbing 1 cm blubber layer for extra protection. More service data for enclosures can be made more available despite limited availability of test animals if a conservative approach to testing is taken.

keywords     alumina, biomaterials, biotelemetry, mechanical testing, Sea Lion, structural ceramics

abstract
Habitat characteristics and mechanisms that enable predators to successfully forage are poorly understood in open marine ecosystems. I addressed this problem in the eastern Bering Sea using animal-born data-loggers carried by lactating northern fur seals (Callorhinus ursinus) from two populations breeding in distinct oceanographic zones ˜ a declining population on St. Paul Island on the continental shelf, and an increasing population on Bogoslof Island over the oceanic basin. The data-loggers recorded water temperatures, dive depths and animal locations throughout foraging trips that lasted as long as 17 days and extended as far as 460 km from the islands. I contrasted tag-derived ocean temperatures with concurrent shipboard measurements and found that the fur seal data revealed finer-scale hydrographic processes with less estimated error than ship-derived data, particularly in dynamic oceanographic areas. I also identified probable foraging hotspots using first-passage time analysis of at-sea locations of individual females, and linked them to fine-scale hydrographic data using habitat selection models. I found that hot spots were related to thermoclines and surface fronts (although not with water temperature), and that the relationships differed between populations and among foraging strategies. St. Paul Island fur seals that mixed epipelagic and benthic dives focused their effort in areas with deeper thermoclines that may concentrate prey closer to the ocean floor, while strictly epipelagic foragers tended to use waters with shallower thermoclines allowing prey to migrate closer to the surface. Fur seals from Bogoslof Island foraged almost exclusively over the Bering Sea basin and appeared to hunt intensively along the fine-scale fronts that surrounded the island while fur seals from St. Paul Island extended their trips off-shelf to forage in areas with similar oceanographic features. It appears that lactating females rely on fine-scale boundaries in the open ocean to effectively concentrate prey, and that the relative distribution and accessibility of these oceanographic features account for the inter-island differences in foraging patterns. Collectively, my thesis shows that wide-ranging, diving animals such as fur seals can be used to produce detailed maps of marine habitat and demonstrates the importance of fine-scale habitat characteristics to top predators foraging in dynamic oceanographic environments.

abstract
Pacific white-sided dolphins (Lagenorhynchus obliquidens) are one of the most abundant cetaceans in British Columbia and throughout the North Pacific Ocean. However, little is known about their seasonal distributions and energy requirements. I analyzed sightings of dolphins attained opportunistically by volunteer observers and from scientific surveysËœand found that Pacific white- sided dolphins have been seen with increased frequency along the BC coast over the past 54 years, and seasonally over the past 8 years. The sightings data showed a southward range shift from the 1950s to 2010, and a seasonal movement from offshore to nearshore waters concurrent with the timing of the herring spawn on the BC coast. I deduced whether seasonal movements reflect seasonal shifts in energy requirements by measuring resting metabolic rates and total energy intake for three captive white-sided dolphins twice per month for one year. Open-circuit gas respirometry revealed relatively high resting metabolic rates (~30 MJ day-1 or ~0.3 MJ kg-1day-1) suggesting that white-sided dolphins may need high-energy prey to fuel their energetic requirements. Average resting metabolic rates of the three dolphins were constant throughout the year despite an increase in food consumption in the fall (October to December). I used these average resting metabolic rates and other parameters associated with growth, activity and assimilation efficiency to inform a generalized bioenergetic model and estimate the food requirements of Pacific white-sided dolphins globally, regionally, and locally. My bioenergetic model predicted that wild dolphins require ~30 MJ day-1 for calves, ~60 MJ day- 1 for juveniles, ~65 MJ day-1 for adults and pregnant females, and ~90 MJ day-1 for lactating females. These energy requirements are ~50% higher than observed for dolphins fed in captivity, and are generally higher than estimates for other similar sized small cetaceans inhabiting temperate waters. My model predicts that an average sized dolphin (78 kg) in the wild would consume ~10 kg of fish per day, or about 13% of its bodyweight. Pairing information about prey requirements and seasonal distributions of dolphins with fisheries data can be used to assess spatial overlap between dolphins and fisheries, and may assist in reducing entanglement, by- catch, and conflict over prey.

keywords     energetics, dolphin, cetacean, food intake, metabolism, distribution, British Columbia, prey

abstract
Quantitative fatty acid signature analysis (QFASA) has been proposed as a technique for determining the long-term diet of animals. The method compares the fatty acid (FA) profiles of predators and potential prey items to estimate relative prey intake. We tested the assumptions of a key step in QFASA, the correction of predator FA signatures for metabolic processes through sets of calibration coefficients (CCs). We conducted long-term controlled feeding studies with captive Steller sea lions consuming herring and eulachon and northern fur seals consuming herring. We compared the results with data from harbour seals eating herring to evaluate the effects of phylogeny and prey type on individual CCs. Even within the limited extended dietary FA subset recommended for use by other researchers, we found that at least 41% of the CCs differed by family (otariid vs. phocid seals) and 58% differed by predator species (sea lion vs. fur seal), suggesting that CCs may be highly species- specific. We also found that 64% of the CCs differed by prey type (sea lions consuming herring vs. eulachon), which raises some fundamental implementation issues. We also found significant differences in diet predictions when the herring- and eulachon-derived sets of CCs were applied to an actual multi-species diet. CCs are presently used as a simple mathematical attempt to describe potentially complex biochemistry. The results of this study raise questions regarding the validity of using CCs derived from an alternative predator species, and highlight some fundamental issues regarding QFASA methodology that need to be addressed through further controlled studies.

abstract
Accurate estimates of food intake and its subsequent affect on growth are required to understand the interaction between an animals‚ physiology and its biotic environment. We determined how food intake and growth of 6 young northern fur seals (Callorhinus ursinus L., 1758) responded seasonally to changes in food availability. Animals were given unrestricted access to prey for 8 hr per day on either consecutive days or on alternate days only. We found animals offered ad libitum food on consecutive days substantially increased their food intake over normal Œtraining‚ levels. However, animals that fasted on alternative days were unable to compensate by further increasing their levels of consumption on subsequent feeding days. Absolute levels of food intake were highly consistent during winter and summer trials (2.7 ˆ 2.9 kg d-1), but seasonal differences in body mass meant that fur seals consumed more food relative to their body mass in summer (~27%) than in winter (~20%). Despite significant increases in absolute food intake during both seasons, the fur seals did not appear to efficiently convert this additional energy into mass growth, particularly in the winter. These seasonal differences in conversion efficiencies and estimates of maximum intake rates can be used to generate physiologically realistic predictions about the effect of changes in food availability on an individual fur as well as the consequences for an entire population.

abstract
Understanding the mechanisms that drive prey selection is a major challenge in foraging ecology. Most studies of foraging strategies have focused on behavioural costs, and have generally failed to recognize that differences in the quality of prey may be as important to predators as the costs of acquisition. Here, we tested whether there is a relationship between the quality of diets (kJ g-1) consumed by cetaceans in the North Atlantic and their metabolic costs of living as estimated by indicators of muscle performance (mitochondrial density, n = 60, and lipid content, n = 37). We found that the cost of living of 11 cetacean species is tightly coupled with the quality of prey they consume. This relationship between diet quality and cost of living appears to be independent of phylogeny and body size, and runs counter to predictions that stem from the well-known scaling relationships between mass and metabolic rates. Our finding suggests that the quality of prey rather than th e sheer quantity of food is a major determinant of foraging strategies employed by predators to meet their specific energy requirements. This predator-specific dependence on food quality appears to reflect the evolution of ecological strategies at a species level, and has implications for risk assessment associated with the consequences of changing the quality and quantities of prey available to top predators in marine ecosystems.

abstract
Wildlife research often requires marking and tagging animals to collect data on survival, reproduction, movement, behaviour and physiology. Identification of individual marine mammals can be carried out using tags, brands, paint, dye, photogrammetry, telemetry and other techniques. An analysis of peer-reviewed articles published from January 1980 to April 2011 addressing the effects of marking revealed a preponderance of studies focussed on short-term effects such as injuries and behavioural changes. Some marking techniques were reported to cause pain and to change swimming and haul-out behaviour, maternal attendance, and duration of foraging trips. However,marking has typically not been found to affect survival. No published research has addressed other possible long-term effects of marking related to injuries or pain responses. Studies of the more immediate effects of marking (mostly related to externally attached devices such as radio-transmitters) have shown a variety of different types and magnitudes of responses. It is important to note that studies failing to find treament differences are less likely to be published, meaning that the present and any other reviews based on published literaturemay be a biased sample of all research conducted on the topic. Publishing results that found no or low impacts (i.e. best practices) as well as those that found significant impacts on animals should both be encouraged. Future research under more controlled conditions is required to document acute effects of marking, including injury and pain, and to better understand longer-term effects on health, reproduction and survival. We recommend that studies using marked animals standardise their reports, with added detail on methodology, monitoring and sampling design, and address practices used to minimise the impact of marking on marine mammals.

abstract
This special publication contains the final report of an independent scientific and economic review of a Biological Opinion (BiOp) issued 24 November, 2010 by the National Marine Fisheries Service (NMFS) on the Fisheries Management Plan (FMP) for the Bering Sea and Aleutian Islands (BSAI) Management Area under a section 7 consultation required by the Endangered Species Act. The BiOp involved the western distinct population segment (WDPS) of Steller sea lions Eumetopias jubatus, the conclusion of which is a finding that fisheries in the western and central Aleutian Islands placed the WDPS in jeopardy of recovery through adverse modification of habitat. The review panel evaluated the scientific evidence and argument given in support of this finding against the scientific requirements of the Endangered Species Act based on consistency, validity, and biologic relevance. The review panel also evaluated the economic analyses that formed the basis for the reasonable and prudent actions arising from the finding. The review panel followed only the terms of reference as published in this final report, and in their deliberations, considered written testimony and testimony provided at two public meetings, one in Seattle on June 2, 2011, and the other in Anchorage on August 22, 2011. The conclusions of the review panel can be found in total in the executive summary and in part at the end of each chapter of the special publication.

abstract
Reconstructing the diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analyzing the soft-matrix of faecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely non-quantitative, which limits their usefulness for some studies. We further developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the proportion of prey in the diets of Steller sea lions (Eumetopias jubatus), a pinniped species thought to be facing significant diet related challenges in the North Pacific. We first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ~12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. We then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions in captivity that were fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7-75% contributions per meal (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally less than 12% for all diets fed. Our findings indicate that real-time PCR of faecal DNA can detect the approximate relative quantity of prey consumed for complex diets and prey species, including cephalopods and fish.

abstract
A review of the available scientific literature reveals a wide range of species holding the remains of sockeye salmon in their stomachs, but only a few of these predators have specialized in targeting sockeye, and there are no studies showing that a predator has consumed sufficient numbers over the past three decades to pose a population threat to sockeye salmon. There is no sign of a smoking gun among the long list of potential predators of Fraser River sockeye salmon. In the open ocean, sockeye salmon appear to draw the predatory attention of salmon sharks, blue sharks, and an obscure species fittingly called daggertooth. All three species likely increased in recent decades (after the 1992 UN ban on driftnet fisheries) ˜ and two of them (salmon sharks and daggertooth) may favor sockeye. Unfortunately, data for these species is also too sparse to draw conclusions about their otential role in the poor return of Fraser River sockeye in 2009, but their life histories suggest relatively stable numbers that should not have exerted greater predation upon sockeye in any single year relative to others. In addition to the daggertooth and sharks, marine mammals also consume adult sockeye salmon. However, sockeye are not an important part of marine mammal diets compared to the other species of salmon. No studies have reported marine mammals consuming sockeye salmon in the open ocean. However, small amounts of sockeye have been found in the stomachs or fecal samples collected from Steller sea lions, northern fur seals, harbour seals, killer whales, and white-sided dolphins feeding over the continental shelf and inside waters of British Columbia. Seal and sea lion populations have increased significantly in British Columbia and southeast Alaska since the late 1970s. However, the available data indicate that sockeye salmon is not a preferred prey species among marine mammals.

abstract
Data on fine-scale animal movement are being collected worldwide, with the number of species being tagged and the resolution of data rapidly increasing. In this study, a general methodology is proposed to understand the patterns in these high-resolution movement time series that relate to marine animal behavior. The approach is illustrated with dive data from a northern fur seal (Callorhinus ursinus) tagged on the Pribilof Islands, Alaska, USA. We apply a state-space model composed of a movement model and corresponding high-resolution vertical movement data. The central goal is to estimate parameters of this movement model, particularly their variation on appropriate time scales, thereby providing a direct link to behavior. A particle filter with state augmentation is used to jointly estimate the movement parameters and the state. A multiple iterated filter using overlapping data segments is implemented to match the parameter time scale with the behavioral inference. The time variation in the auto-covariance function facilitates identification of a movement model, allows separation of observation and process noise, and provides for validation of results. The analysis yields fitted parameters that show distinct time-evolving changes in fur seal behavior over time, matching well what is observed in the original data set.

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Locomotion is one of the major energetic costs faced by animals and various strategies have evolved to reduce its cost. Birds use interspersed periods of flapping and gliding to reduce the mechanical requirements of level flight while undergoing cyclical changes in flight altitude, known as undulating flight. Here we equipped free-ranging marine vertebrates with accelerometers and demonstrate that gait patterns resembling undulating flight occur in four marine vertebrate species comprising sharks and pinnipeds. Both sharks and pinnipeds display intermittent gliding interspersed with powered locomotion. We suggest, that the convergent use of similar gait patterns by distinct groups of animals points to universal physical and physiological principles that operate beyond taxonomic limits and shape common solutions to increase energetic efficiency. Energetically expensive large-scale migrations performed by many vertebrates provide common selection pressure for efficient locomotion, with potential for the convergence of locomotory strategies by a wide variety of species.

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Behavioural observations are fundamental to understanding and defining the habitat needs of animals. I compiled the behavioural repertoires reported for harbour (Phocoena phocoena) and Dall’s porpoise (Phocoenoides dalli) by classifying the life processes of phocoenids into 12 descriptive categories. This range-wide review revealed complex sexual and social behaviours, similar foraging behaviours and breeding site fidelity, as well as differences in habitat selection between these two northern hemisphere species. I also conducted a fine-scale field study of harbour porpoise foraging behaviour at two sites in Juan de Fuca Strait (British Columbia) using point transect survey data (2007–2008), and platforms of opportunity data (1995–1996, 1998–2008) to determine the physical conditions under which harbour porpoise foraged and the extent to which they displayed specialised behaviours. I examined harbour porpoise presence, density and group sizes relative to tidal currents, tidal variation, lunar phase, lunar position, solar position, diurnality, seasonality and presence of conspecifics—and found that greater numbers of harbour porpoise occurred on the ebb current during the spring tides. Numbers of porpoise increased three-fold between April and October, when calves and high-energy behaviours were also more prevalent. To identify porpoise breeding habitat in the inland waters of southern British Columbia and northwestern Washington, I used systematically and opportunistically collected sightings of harbour and Dall’s porpoise (1991–2008), and compared group sizes and frequency of occurrences for both species relative to bathymetry and tidal speeds. Overall, I found that both species selected bathymetrically differentiated habitats that were characterized by high rates of tidal mixing (with harbour porpoise preferring regions ≤100 m, and Dall’s porpoise preferring 151 – 250 m). Spatial analysis identified two separate areas that may be species-specific breeding habitats—the first to be identified for either species in this region. In summary, harbour porpoise maintained stable group sizes and used tidally well-mixed foraging sites on a temporary but predictable basis. Dall’s porpoise were associated with these same areas, but habitat partitioning associated with differences in bathymetry occurred in important breeding areas that may account for the coastal parapatric distribution of these two high trophic level predators.

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Information concerning mechanistic processes underlying changes in vital rates and ultimately population growth rate is required to monitor impacts of environmental change on wildlife. We estimated age-specific survival and examined factors influencing survival for a threatened population of Steller sea lions (Eumetopias jubatus) in southeastern Alaska. We used mark-recapture models and data from 1,995 individuals marked at approximately one month of age at four of five rookeries in southeastern Alaska, and resighted from Oregon to the Bering Sea. Average annual survival probability for females was .64 for pups and 0.77 for yearlings, and increased from 0.91 to 0.96 from age 3ˆ7 yrs. Annual survival probability of males averaged 0.60 for pups and 0.88 by 7 yrs, resulting in probability of survival to age 7, 33% lower for males compared to females. Pups from northern southeastern Alaska (including an area of low summer population size but rapid growth) were twice as likely to survive to age 7 compared to pups from southern rookeries (including a large, historical, stable rookery). Effects of early conditions on future fitness were observed as (1) environmental conditions in the birth year equally affected first- and second year survival, and (2) effects of body mass at approximately one month of age were still apparent at 7 yrs. Survival from 0ˆ2 yrs varied among five cohorts by a maximum absolute difference of 0.12. We observed survival costs for long-distance dispersal for males, particularly as juveniles. However, survival was higher for non-pups that dispersed to northern southeastern Alaska, suggesting that moving to an area with greater productivity, greater safety, or lower population size may alleviate a poor start and provide a mechanism for spatial structure for sea lion populations.

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A leading hypothesis to explain the decline of Steller sea lions (Eumetopias jubatus) in western Alaska is the reduction of prey abundance or change in prey distributions caused by commercial fisheries. We sought to improve on past studies that attempted to assess competition between sea lions and fisheries by estimating the local amounts of prey accessible to sea lions. We explored the relationships between sea lion population trends, fishery catches and the prey biomass accessible to sea lions around 33 rookeries from 2000-2008. We focused on three commercially important species that dominate the sea lion diet: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estimate the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass (estimated using our accessibility model and also within 10, 20 and 50 km of each rookery). Of the 304 statistical models we constructed to compare accessible prey biomass and catch to sea lion population trends, only three relationships were significant. These three suggest that sea lion population change rates increased (became less negative) with increasing accessible pollock biomass in the Aleutian Islands and with cod biomass in the Gulf of Alaska. No relationships were found between sea lion population trends and Atka mackerel biomass. Given that the majority of the relationships we explored were insignificant, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s. Sea lion population trends appeared to be affected by some unknown factor associated with regional differences. Removing fish catches or adding catch to our predicted distributions of groundfish abundances had no measurable effect on sea lion population trends. These observations suggest that sea lion populations were largely unaffected by fishery removals during this period.

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Measurements of the electrophysiological auditory steady-state response (ASSR) have proven to be efficient for evaluating hearing sensitivity in odontocete cetaceans. In an effort to expand these methods to pinnipeds, ASSRs elicited by single and multiple simultaneous tones were used to measure aerial hearing thresholds in several California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus). There were no significant differences between thresholds measured using the single and multiple ASSR methods, despite the more rapid nature of data collection using the multiple ASSR method. There was a high degree of variability in ASSR thresholds among subjects; thresholds covered a range of ~40dB at each tested frequency. As expected, ASSR thresholds were elevated relative to previously reported psychophysical thresholds for California and Steller sea lions. The features of high-frequency hearing limit and relative sensitivity of most ASSR audiograms were, however, similar to those of psychophysical audiograms, suggesting that ASSR methods can be used to improve understanding of hearing demographics in sea lions, especially with respect to high-frequency hearing. Thresholds for one Steller sea lion were substantially elevated relative to all other subjects, demonstrating that ASSR methods can be used to detect hearing loss in sea lions.

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Public signaling plays an important role in territorial and sexual displays in animals; however, in certain situations, it is advantageous to keep signaling private to prevent eavesdropping by unintended receivers. In the northeastern Pacific, two populations of killer whales (Orcinus orca), fish-eating resident killer whales and mammal-eating transient killer whales, share the same habitat. Previous studies have shown that residents use whistles as private signals during close-range communication, where they probably serve to coordinate behavioral interactions. Here, we investigated the whistling behavior of mammal-eating killer whales, and, based on divergent social structures and social behaviors between residents and transients, we predicted to find differences in both whistle usage and whistle parameters. Our results show that, like resident killer whales, transients produce both variable and stereotyped whistles. However, clear differences in whistle parameters between ecotypes show that the whistle repertoire of mammal-eating killer whales is clearly distinct from and less complex than that of fish-eating killer whales. Furthermore, mammal-eating killer whales only produce whistles during milling after kill and surface-active behaviors, but are almost completely silent during all other activities. Nonetheless, whistles of transient killer whales may still serve a role similar to that of resident killer whales. Mammal-eating killer whales seem to be under strong selection to keep their communication private from potential prey (whose hearing ranges overlap with that of killer whales), and they appear to accomplish this mainly by restricting vocal activity rather than by changes in whistle parameters.

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Five years of behavioral observations revealed significant effects of high air temperatures and breeding site topography on the mating system of South American sea lions in Peru. Unlike most polygynous mammals that defend females or fixed territories, male sea lions in Peru maintained positions along the shoreline where females passed each day to thermoregulate, and where most copulations occurred. Sex ratios (1 male per 17 females) and male mating success were extremely skewed (14% of males achieved 50% of the copulations, and 25% of them did not copulate at all). The mass daily movements of females toward the water and cool substrate of the shoreline, along with a highly skewed sex ratio, accentuated the difficulty for males to monopolize and restrict female movements. Femalesmoved freely and chose their mates, unlike in temperate regions of their range where male South American sea lions control groups of females or access to tide pools. Our observations indicate that the South American sea lion in Peru has a lek-like breeding system. This is a rare alternative to the common male strategies of defending females and resources, and is likely an evolutionary product of their highly skewed sex ratio, protracted breeding season, and the extreme subtropical climate where they breed.

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Evidence suggests that Pacific harbor seals Phoca vitulina are likely to alter their foraging behavior in response to seasonal prey pulses. We hypothesized that spawning herring Clupea pallasii aggregations are seasonally important prey for harbor seals, predicting that (1) harbor seal consumption of adult herring would peak during the spawning season, (2) harbor seals would seasonally change their foraging areas to take advantage of spawning herring aggregations, and (3) seal diving behavior would reflect the vertical distribution of herring during the spawning season. The predictions were tested using an analysis of harbor seal prey remains, GPS telemetry, and satellite-linked time/depth recorder data. Contrary to predictions, herring in harbor seal diet was comprised of 74% juveniles and 26% adults in the spawn season, versus 37% juveniles and 63% adults in the post-spawn season. Harbor seal use of documented herring areas was highest during the season when herring did not spawn, and seal diving behavior did not reflect the vertical distribution of herring. The lack of response by harbor seals to spawning herring pulses is likely explained by the low energy density of adult herring during the spawn season, and the availability of profitable alternative prey such as juvenile herring. This study highlights the influence of relative prey profitability on the foraging behavior of harbor seals, and may help to explain why predators do not always respond as predicted to resource pulses.

abstract
Ecosystem-based management (EBM) of marine resources attempts to conserve interacting species. In contrast to single-species fisheries management, EBM aims to identify and resolve conflicting objectives for different species. Such a conflict may be emerging in the northeastern Pacific for southern resident killer whales (Orcinus orca) and their primary prey, Chinook salmon (Oncorhynchus tshawytscha). Both species have at-risk conservation status and transboundary (CanadaˆUS) ranges. We modeled individual killer whale prey requirements from feeding and growth records of captive killer whales and morphometric data from historic live-capture fishery and whaling records worldwide. The models, combined with caloric value of salmon, and demographic and diet data for wild killer whales, allow us to predict salmon quantities needed to maintain and recover this killer whale population, which numbered 87 individuals in 2009. Our analyses provide new information on cost of lactation and new parameter estimates for other killer whale populations globally. Prey requirements of southern resident killer whales are difficult to reconcile with fisheries and conservation objectives for Chinook salmon, because the number of fish required is large relative to annual returns and fishery catches. For instance, a U.S. recovery goal (2.3% annual population growth of killer whales over 28 years) implies a 75% increase in energetic requirements. Reducing salmon fisheries may serve as a temporary mitigation measure to allow time for management actions to improve salmon productivity to take effect. As ecosystem-based fishery management becomes more prevalent, trade-offs between conservation objectives for predators and prey will become increasingly necessary. Our approach offers scenarios to compare relative influence of various sources of uncertainty on the resulting consumption estimates to prioritise future research efforts, and a general approach for assessing the extent of conflict between conservation objectives for threatened or protected wildlife where the interaction between affected species can be quantified.

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The predictive relationship between heart rate (fH) and oxygen consumption (VO2) has been derived for several species of marine mammals swimming horizontally or diving in tanks to shallow depths. However, it is unclear how dive activity affects the fH:VO2 relationship and whether the existing equations apply to animals diving to deeper depths. We investigated these questions by simultaneously measuring the fH and VO2 of Steller sea lions (Eumetopias jubatus) under different activity states (surface resting or diving), types of dives (single dives or dive bouts), and depths (10 or 40m). We examined the relationship over dives only and also over dive cycles (dive + surface interval). We found that fH could only predict VO2 over a complete single dive cycle or dive bout cycle (i.e. surface intervals had to be included). The predictive equation derived for sea lions resting on the surface did not differ from that for single dive cycles. However, the equation derived over dive bout cycles multiple dives + surface intervals) differed from those for single dive cycles or surface resting, with similar fH for multiple dive bout equations yielding higher predicted VO2 than that for single dive bout cycles (or resting). The fH:VO2 relationships were not significantly affected by dive duration, dive depth, water temperature or cumulative food consumed under the conditions tested. Ultimately, our results demonstrate that fH can be used to predict activity-specific metabolic rates of diving Steller sea lions, but only over complete dive cycles that include a post-dive surface recovery period.

abstract
The ability to use heart rate (fh) to predict oxygen consumption rates (VO2) in Steller sea lions and other pinnipeds has been investigated in fasting animals. However, it is unknown whether established fh:VO2 relationships hold under more complex physiological situations, such as when animals are feeding or digesting. We assessed whether fh could accurately predict VO2 in trained Steller sea lions while fasting and after being fed. Using linear mixed-effects models, we derived unique equations to describe the fh:VO2 relationship for fasted sea lions resting on land and in water. Feeding did not significantly change the fh:VO2 relationship on land. However, Steller sea lions in water displayed a different fh:VO2 relationship after consuming a 4 kg meal compared to the fasting condition. Incorporating comparable published fh:VO2 data from Steller sea lions showed a distinct effect of feeding after a 6 kg meal. Ultimately, our study illustrated that both feeding and physical environment are statistically relevant when deriving VO2 from telemetered fh, but that only environment affects the practical ability to predict metabolism from fh. Updating current bioenergetic models with data gathered using these predictive fh:VO2 equations will yield more accurate estimates of metabolic rates of free-ranging Steller sea lions under a variety of physiological, behavioral, and environmental states.

abstract
Like many endangered wildlife populations, the viability and conservation status of ‘southern resident’ killer whales Orcinus orca in the north-east Pacific may be affected by prey limitation and repeated disturbance by human activities. Marine protected areas (MPAs) present an attractive option to mitigate impacts of anthropogenic activities, but they run the risk of tokenism if placed arbitrarily. Notwithstanding recreational and industrial marine traffic, the number of commercial vessels in the local whalewatching fleet is approaching the number of killer whales to be watched. Resident killer whales have been shown to be more vulnerable to vessel disturbance while feeding than during resting, travelling or socializing activities, therefore protected-areas management strategies that target feeding ‘hotspots’ should confer greater conservation benefit than those that protect habitat generically. Classification trees and spatially explicit generalized additive models were used to model killer whale habitat use and whale behaviour in inshore waters of Washington State (USA) and British Columbia (BC, Canada). Here we propose a candidate MPA that is small (i.e. a few square miles), but seemingly important. Killer whales were predicted to be 2.7 times as likely to be engaged in feeding activity in this site than they were in adjacent waters. A recurring challenge for cetacean MPAs is the need to identify areas that are large enough to be biologically meaningful while being small enough to allow effective management of human activities within those boundaries. Our approach prioritizes habitat that animals use primarily for the activity in which they are most responsive to anthropogenic disturbance.

abstract
Knowing how species will respond to environmental variability and climate change requires understanding the factors that influence their distribution and movement patterns. I investigated the processes that drive individuals to concentrate in specific areas of their home range by modeling encounter rates of humpback whales (Megaptera novaeangliae) in relation to environmental variables using GIS tools, generalized additive models, and remote sensing and in situ data. I conducted this work at two foraging areas: the coastal waters of British Columbia, Canada, and the Bransfield and Gerlache Straits, Antarctica. Humpback whales in British Columbia were strongly associated with latitude and bathymetric features. The relationships with remotely sensed variables reflecting primary productivitywere not consistent, but higher numbers of whales seemed to be associated withhigherproductivity. In fact, the highest concentrations of humpback whales appeared to reflect areas whereconcentration and retention processes lead to higher biological productivity, including south Dixon Entrance, middle and southwestern Hecate Strait and off Juan de Fuca Strait. Humpback whales in the Southern Ocean also preferred areas of enhanced biological productivity. In Gerlache Strait, humpback whales were associated with areas of higher chlorophyll-a concentration in the central and northern sections of the strait, which also corresponded to relatively higher temperatures and shallower mixed layer depths for the in situ data. In Bransfield Strait, humpback whales appeared to prefer the near-frontal zones and the deep basins, where surface waters are influenced by the Bransfield Current. Interannual variability in both humpback and minke whale encounter rates in Gerlache Strait was correlated with the Oceanic Niño Index, the oceanic component of ENSO. In addition to investigating species-habitat relationships with statistical models, I conducted the first study to describe the satellite-monitored movements of humpback whales on their feeding grounds along the Antarctic Peninsula. Results showed considerable individual variation in direction, speed and range of movements, and an overall pattern characterized by short- and long-distance movements between presumed foraging areas with relatively short residency times. All told, the results of my research show that humpback whale distribution within foraging habitat is influenced by physical and biological variables that enhance biological productivity.

abstract
King penguins Aptenodytes patagonicus are known to change their diving behaviour in response to changes in both prey location and their breeding status through the early stages of the breeding cycle (austral summer and autumn). However, little information exists on whether and how these changes affect the energy expenditure of such behaviour. By deploying heart rate and hydrostatic pressure data loggers, we investigated detailed changes in the dive time budgeting of king penguins during foraging dives across the breeding season, in the same individuals, and the associated changes in estimated oxygen consumption during those dives. Maximum dive depth, duration, bottom duration, feeding events (indicated by wiggles) per dive and post-dive duration increased through the study period. While a foraging dive later in the breeding season was energetically more costly than a dive earlier in the season, the overall rate of energy expenditure did not change, nor did energy cost per unit prey capture. These findings indicate an ability of king penguins to adjust their foraging dive behaviours through the summer and autumn without affecting the energetic costs of diving to capture prey. Such plasticity may be necessary to compensate for changes both in prey location and abundance, and in the energy requirements of the chick over time.

abstract
Transit costs associated with commuting between resting sites ashore and foraging areas at sea are an appreciable portion of foraging expenditures in pinnipeds. We examined transit swimming in three Steller sea lions (Eumetopias jubatus) trained to follow a moving boat at different speeds and depths. We measured dive behavior (duration) and focused specifically on activity measures (fore-flipper stroking and ODBA, an overall measure of body motion), which may be proxies for metabolic expenditure. Sea lions appeared to increase efficiency while transiting at depths that approached three times their body diameters (mean depth = 151 ± 1 cm SEM, n = 87). Although the response was not uniform for all tested scenarios, all of the significant adjustments we observed to dive behavior and swimming mechanics supported an increased efficiency at this depth. An increase in transit speed (4.5 versus 3.5 knots surface speed) was associated with elevated flipper stroke frequencies (+5%) and stroke output (ODBA•stroke-1, +48%). Sea lions transiting against the flow of a tidal current had reduced dive durations (-10%), while total ODBA was consistently elevated (+8% overall). This response to tidal flow was accompanied either by elevated ODBA•stroke-1 (3.5 knots) or a parallel increase in stroking (4.5 knots). Our data demonstrate that small changes in the physical environment affect transiting in Steller sea lions, and imply that altered prey fields or changing ocean conditions can carry energetic consequences.

abstract
Muscle exercise correlates with oxygen use, tissue perfusion and heart rate (fH) in terrestrial animals, but the relationship between these physiological processes is less clear in diving animals. We found the mean heart rate of Steller sea lions trained to voluntarily dive to depths up to 40m dropped by 40% while diving, and noted that mean bradycardia was 9% greater during shallow (10m) compared to deep (40m) dives. Longer dives resulted in lower heart rates, but only when they were shallow; on the other hand, minimum instantaneous fH decreased consistently with dive duration. In general, instantaneous fH did not reflect activity over short timescales. Our data suggest that our sea lions invoked a different dive response depending on whether they dove to shallow or deep depths. During shallow (10m) dives only, the correlation between activity and fH was indicative of vascular compromise between diving and exercise. However, during deep dives (40m), there was no such correlation, suggesting that locomotory activity was uncoupled from dive bradycardia, which was possibly mediated by an absence of blood flow to active muscle. For both diving scenarios, surface fH correlated with dive activity, suggesting that some underwater locomotory costs were deferred to the post-dive surface interval. Ultimately, our data support the speculation that Steller sea lion locomotory muscles become hypoxic during diving, regardless of dive depth.

abstract
Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24 h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. The peak T3 response occurred 48 h post injection in three animals and 71 h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.

abstract
Capturing the global benefits of biodiversity requires sacrifice from us all, not only in financial terms (e.g. higher taxes and foregone profits) but also in terms of personal risk, material losses, freedom of action or convenience. Our common task should not only be to focus on research, but also on communicating to non-scientists both the merits and challenges of maintaining biodiversity and presenting the practical measures that can be deployed to achieve this goal. Open dialogue of the trade-offs involved in biodiversity conservation actions leads to the types of democratic decision making, increased sense of community and social justice, and respect for indigenous, rural and local ways of life that are hallmarks of successful conservation programs.

abstract
Mammal-eating killer whales (Orcinus orca(L., 1758)) are a rare example of social predators that hunt together in groups of sexually dimorphic adults and juveniles with diverse physiological diving capacities. Dayˆnight ecological differences should also affect diving as their prey show diel variation in activity and mammal-eating killer whales do not rely on echolocation for prey detection. Our objective was to explore the extent to which physiological aerobic capacities versus ecological factors shape the diving behaviour of this breath-hold diver. We used suction-cup-attached depth recorders (Dtags) to record 7608 dives of 11 animals in southeast Alaska. Analysis of dive sequences revealed a strong bout structure in both dive depth and duration. Dayˆnight comparisons revealed reduced rates of deep dives, longer shallow dives, and shallower long-duration dives at night. In contrast, dive variables did not differ by ageˆsex class. Estimates of the aerobic dive limit (cADL) suggest that juveniles exceeded their cADL during as much as 15% of long dives, whereas adult males and females never exceeded their cADL. Mammal-eating killer whales in this area appear to employ a strategy of physiological compromise, with smaller group members diving nearer their physiological limits and large-bodied males scaling down their physiological performance.

abstract
Male Juan Fernández fur seals (Arctocephalus philippii) are significantly larger than females at birth and show extreme dimorphism as adults. We investigated morphological differences among male and female pups using a cross-sectional sampling design to evaluate whether pup growth rates during the breeding season were sex-specific. We characterized growth rates using mass, length, and girth and found that length was the least variable measure of body growth (based on the coefficients of variation for the three measures of body size). Male pups were heavier on average than female pups on any given day of sampling but did not grow faster than females. No significant differences were noted in the body conditions of male and female pups. These findings suggest that the sexual differences among A. philippii pups originate before birth and are not accentuated while suckling during the breeding season.

abstract
Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.

abstract
Stable isotope analysis is often used to examine diet choice and tropic relationships in marine mammals. However, the technique makes a number of largely untested assumptions. For example, researchers often assume localized biopsies to be representative of the whole animal—that is, that the isotopic signal is homogenous within a tissue. Further, isotopic composition may differ across the body within the same tissue type due to differential assimilation or catabolization rates. We investigated the homogeneity of 13C and 15N values in skin and muscle across the body per individual in three pinniped species: Steller sea lions (Eumetopias jubatus, n = 5), California sea lions (Zalophus californianus, n = 6), and harbor seals (Phoca vitulina, n = 7). We also assessed if there are consistent carbon and nitrogen isotope differences between these two commonly sampled tissues. Our results show that skin tissue was significantly 13C enriched when compared to muscle tissue, and more difficult to properly process. Despite expected differences across the body in physiological processes and biochemical composition, our data indicate stable isotope signal homogeneity across the body within both muscle and skin, for both carbon and nitrogen isotopes, in all three species. These results indicate that sufficient homogeneity exists within skin and muscle tissues to suggest that point sampling can be considered representative of entire tissues, and is thus a valid technique in stable isotope studies of marine mammals.

abstract
We attached accelerometers to the head and jaw of a Steller sea lion (Eumetopias jubatus) to determine whether feeding attempts in a controlled setting could be quantified by acceleration features characteristic of head and jaw movements. Most of the 19 experimental feeding events that occurred during the 51 dives recorded resulted in specific acceleration patterns that were clearly distinguishable from swimming accelerations. The differential acceleration between the head-mounted and jaw-mounted accelerometers detected 84% of prey captures on the vertical axis and 89% on the horizontal axis. However, the jaw-mounted accelerometer alone proved to be equally effective at detecting prey capture attempts. Acceleration along the horizontal (surge)-axis appeared to be particularly efficient in detecting prey captures, and suggests that a single accelerometer placed under the jaw of a pinniped is a promising and easily implemented means of recording prey capture attempts.

abstract
A concentration of pelagic sharks was observed in an area of western Queen Charlotte Sound, British Columbia, during systematic shipboard line-transect surveys conducted (2004 to 2006) for marine mammals throughout coastal waters of British Columbia. Surveys allowed only brief observations of sharks at the surface, providing limited opportunity to confirm species identity. Observers agreed, however, that salmon sharks Lamna ditropis (Lamnidae) were most common, followed by blue sharks Prionace glauca (Carcharhinidae). Both conventional and model-based distance sampling statistical methods produced large abundance estimates (~20000 sharks of all species combined) concentrated within a hotspot encompassing ~10% of the survey region. Neither statistical method accounted for submerged animals, thereby underestimating abundance. Sightings were made in summer, corresponding with southern movement of pregnant salmon sharks from Alaska. The previously undocumented high density of these pelagic sharks in this location has implications for understanding at-sea mortality of returning Pacific salmon Oncorhynchus spp. (Salmonidae) and for assessing conservation status of sharks in Canada and beyond. We recommend that a dedicated Canada-US sightings and biological sampling programme be considered, perhaps under the UN Transboundary Species Fishery programme.

abstract
Despite its essential role in bioenergetic modeling, reliable measures of energy expenditure (i.e., oxygen consumption) associated with the different activities of wild animals have remained elusive. Oxygen consumption rate (VOâ‚‚) associated with activity can be estimated as a function of heart rate (fh), and the empirical relationship between the two has been determined for several aquatic vertebrates while fasting and resting. However, the simplified fh:VOâ‚‚ relationships established from such studies may differ under more complex physiological circumstances, such as when animals are foraging at depth or feeding on prey. I assessed the efficacy of using fh to predict VOâ‚‚ in 7 captive Steller sea lions, Eumetopias jubatus, while fasting and feeding at rest (on land or in water) and while diving (up to 40 m in the open ocean). Linear mixed-effects models revealed that environment, amount of food fed, and type of diving activity all altered the fh:VOâ‚‚ relationship. They also showed that different linear equations are needed to predict VOâ‚‚ from fh for sea lions fasted while on land or in water, but that a single equation can predict VOâ‚‚ on land regardless of whether fasted or feeding. When in water, feeding animals a 4, 6, or 12 kg meal changed the fh:VOâ‚‚ relationship compared to fasted animals. While fh can reliably be used to predict VOâ‚‚ in diving sea lions, the relationship differed between single dive cycles (one dive +surface interval) and dive bout cycles (multiple dives+surface intervals). However, the equation that predicted VOâ‚‚ for single dive cycles did not differ from that for sea lions resting on the surface. Neither dive duration, dive depth, nor food consumed significantly affected the fh:VOâ‚‚ relationships. Heart rate could be used to predict VOâ‚‚ in diving sea lions, but only over complete dive cycles or dive bouts where animals recovered fully from the Oâ‚‚ debt incurred underwater. Based on these results, separate equations that distinguish among environmental, digestive, and diving states can be employed to accurately predict VOâ‚‚ from heart rate in wild Steller sea lions.

abstract
Morphometric measurements and daily feeding records of 62 captive Steller sea lions (Eumetopias jubatus) were analyzed to provide information about seasonal growth and food consumption that has been impossible to collect from wild animals. Data from nursing pups, intact and castrated males, pregnant, lactating and non-reproductive females were also used to determine differences in rates of maturity between males and females, and the effects that climate, sexual maturity, castration and pregnancy and lactation have on growth and food intake. Data were fit with seasonal (sine function) and annual (von Bertalanffy, logistic, Gompertz, Richard’s and maturity) growth models, and showed that males achieved larger body sizes than females by undergoing a growth spurt during puberty and by extending their growth throughout adulthood. Annual increases in the length and mass of females slowed significantly following sexual maturity. Males and females both experienced seasonal oscillations in body mass, but the seasonal fluctuation in male mass peaked later (April) and was far more dramatic than that of females. The mass of lactating and non-reproductive females peaked in early spring (March), while increases in the mass of pregnant females paralleled fetal growth, reaching a maximum before parturition. Changes in mass did not parallel changes in consumption. Fish intake by males and females peaked during winter and bottomed during late spring, while seasonal changes in body mass reached their high and low 3 to 4 months later than food intake. Pregnant and non-reproductive females differed little in the amount of prey they consumed, unlike lactating females that significantly increased their consumption during summer and winter. The differences between females highlight the relatively low additional energetic requirements of pregnancy and the high costs of lactation. Differences between neutered and intact males further suggest that testosterone affected overall male growth, but had smaller effects of seasonal oscillations in mass and did not affect food intake. The reproductive cycle and thermoregulatory requirements appeared to drive seasonal changes in body mass and food intake of male and female Steller sea lions but at different time scales. Our findings also indicate that mass is not a simple reflection of food intake, which has important implications for future nutritional research and bioenergetic modeling of wild pinnipeds.

abstract
Determining diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analyzing the soft matrix of fecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely non-quantitative, which limits their applicability. I developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the diets of Steller sea lions (Eumetopias jubatus). I first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ~12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. I then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions that had been fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7-75% contributions to a meal mix (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally less than 12% for all diets fed when percentages of prey consumed were corrected for differences in mtDNA density among the prey items. My findings indicate that real-time PCR can detect the quantity of prey consumed for a variety of complex diets and prey species, including cephalopods and fish.

abstract
hirty-six aluminum oxide laminated discs were implanted into 12 young rabbits (18 with a 0.5 mm porous layer and 18 with 1 mm) to determine whether implants that are porous only on one side could fixate to subcutaneous tissue. After 3 months, discs were encased within thin pouches (0.02-0.14 mm) of fibrous connective tissue, as would have been expected of a completely porous implant. Solid sides showed no while the porous sides showed little attachment to pouches. 47% (17) of the discs had moved 1.4±0.8 cm beyond the 4.7 + 1 cm they had moved due to normal skin growth, while two others had moved between 6.2 and 6.5 cm beyond this measure. The proportion of 1 mm porous layer discs migrating within subcutaneous tissue was no greater than the proportion of 0.5 mm layer discs migrating (p=0.15). Porous layer height and disc migration did not affect the attachment strength of pouch to surrounding tissues (68 ±23 N, p=0.34). Pouch thickness, which has been associated to the level of applied forces in other studies, increased with migration distance (p=0.054). Results indicate that one sided porous disks are likely easier to retrieve than completely porous ones, but cannot be prevented from migrating in loose tissue of young animals. Data is being used to design subdermal radio frequency devices for endangered marine animals.

abstract
Physiological responses to changes in energy balance are tightly regulated by the endocrine system through glucocorticoids, IGF-I and thyroid hormones. Changes in these hormones were studied in eight captive female Steller sea lions that experienced changes in food intake, body mass, body composition, and blood metabolites during summer and winter. During a period of energy restriction, one group of sea lions was fed reduced amounts of Pacific herring and another was fed an isocaloric diet of walleye pollock, after which both groups returned to their pre-experimental diets of herring. Cortisol was negatively and IGF-I was positively associated with changes in body mass during periods of energy restriction (mass loss associated with increase in cortisol and decrease in IGF-I) and refeeding (body mass maintenance associated with stable hormone concentrations in summer and compensatory growth linked to decrease in cortisol and increase in IGF-I in winter). Cortisol and IGF-I were also correlated with changes in lipid and lean mass, respectively. Consequently, these two hormones likely make adequate biomarkers for nutritional stress in sea lions, and when combined provide indication of the energetic strategy (lipid vs lean mass catabolism) animals adopt to cope with changes in nutrient intake. Unlike type of diet fed to the sea lions, age of the animals also impacted hormonal responses, with younger animals showing more intense hormonal changes to nutritional stress. Thyroid hormones, however, were not linked to any physiological changes observed in this study.

abstract
Two groups of female Steller sea lions (Groups H and P) were subjected to periods of energy restriction and subsequent re-feeding during winter and summer to determine changes in energy partition among principal physiological functions and the potential consequences to their fitness. Both sea lion groups consumed high-quality fish (herring) before and after the energy restrictions. During restrictions, Group H was fed a lower quantity of herring and Group P a caloric equivalent of low-quality fish (pollock). Quantitative estimates of maintenance and production energies and qualitative estimates of thermoregulation, activity and basal metabolic rate were measured. During summer, all animals compensated for the imposed energy deficit by releasing stored energy (production energy). Group H also optimized the energy allocation to seasonal conditions by increasing activity during summer when fish are naturally abundant (foraging effort) and by decreasing thermoregulation capacity when waters are warmer. During winter, both groups decreased the energy allocated to overall maintenance functions (basal metabolic rate, thermoregulation and activity together) in addition to releasing stored energy, but preserved thermoregulatory capacity. Group H also decreased activity levels in winter when foraging in the wild is less efficient, unlike Group P. Overall, sea lions fed pollock did not change energy allocation to suit environmental conditions as readily as those fed herring. This implies that low energy density diet may further reduce fitness of animals in the wild during periods of nutritional stress.

abstract
Reduced availability of high energy-content prey (nutritional stress) is a predominant hypothesis to explain the decline of Steller sea lion (Eumetopias jubatus) populations in western Alaska from the late 1970's to the late 1990's. Animals may respond to eating insufficient prey by increasing stress levels and decreasing metabolic rates. It may thus be possible to identify nutritional stress by measuring concentrations of GC metabolites (stress) and thyroid hormones (metabolism) shed in the feces of Steller sea lions. However, techniques to measure thyroid hormone concentrations from sea lion feces have not been developed. We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in Steller sea lion feces following two injections of thyrotropin (TSH) at 24 h intervals into four captive animals. Glucocorticoid (GC) metabolites were also assayed to examine any relationship to stimulated thyroid hormone secretion. We found that fecal T3 peaked 48 h post-injection and increased 25-57% in three sea lions (all animals, p=0.03). Pre-injection GC increases indicated stress from isolation for baseline fecal collections, but post-injection increases could not be confirmed as a response to TSH injections or as a product of the study design. The results demonstrated that pre- and post-injection changes in fecal GC and T3 concentrations were consistent with predictions of an increased stress response and metabolic rate within the animals. We then measured T3 and GC concentrations in 834 Steller sea lion fecal samples collected in 2005 and 2006 from 15 resting (haulout) and breeding (rookery) sites between British Columbia and the Central Aleutian Islands. Overall, GC concentrations did not differ between haulout populations (western 2006 pre-pupping and eastern 2005 post-pupping). Fecal hard-part analyses revealed a lower energy-content diet in the western population, suggesting that diet quality is a relevant hypothesis to explain slightly higher GC concentrations found in the western population, specifically the Aleutian Islands region. However, the nutritional stress hypothesis could not be substantiated through T3 concentrations. The rookeries possessed the highest energy-content diets, but also exhibited a nutritional stress response with a significantly higher GC and lower T3 concentration than either haulout population (possibly related to lactation or decreased leptin levels), but T3 comparisons performed at scales of site and region were inconclusive.

abstract
Vessel traffic may have contributed to southern resident killer whales Orcinus orca becoming endangered. To determine the importance of this threat, we measured the behavior of southern residents in the presence and absence of vessels from 2003 to 2005 at 2 different sites along San Juan Island, Washington, USA. We observed activity states of killer whale schools using scan sampling and collected information on the number of vessels present at various distances from those. We use first-order, time-discrete Markov chains to estimate state-transition probability matrices under varying boat exposure conditions. Transition probabilities between activity states were significantly affected by vessel traffic. In addition, there was a reduction in time spent foraging, as estimated from the stationary state budget from the Markov chains, confirming an effect also previously observed in northern resident killer whales. If reduced foraging effort results in reduced prey capture, this would result in decreased energy acquisition. Each school was within 400 m of a vessel most of the time during daylight hours from May through September. The high proportion of time southern resident killer whales spend in proximity to vessels raises the possibility that the short-term behavioral changes reported here can lead to biologically significant consequences.

abstract
Nine Steller sea lions (Eumetopias jubatus) aged 1.756 yr were experimentally fasted for 714 d during the breeding and nonbreeding seasons to identify changes in plasma metabolites that are indicative of fasting and to determine whether the ability of sea lions to fast varies seasonally or with age. Although some animals approached the limit of their protein-sparing ability by the end of our fasting experiments, there was no sign of irreversible starvation biochemistry. Plasma blood urea nitrogen (BUN) concentrations decreased in all animals within the first week of fasting, reflecting a shift to a fasting-adapted state; however, significant increases in plasma BUN concentration at the end of the nonbreeding season fasts suggest that subadult Steller sea lions were not able to maintain a protein-sparing metabolism for a full 14 d during the nonbreeding season. In contrast, juveniles were able to enter protein sparing sooner during the nonbreeding season when they had slightly higher initial percent total body lipid stores than during the breeding season. Subadult and juvenile sea lions had low circulating ketone body concentrations compared with young sea lion pups, suggesting an age-related difference in how body reserves are utilized during fasting or how the resulting metabolites are circulated and catabolized. Our data suggest that metabolite concentrations from a single blood sample cannot be used to accurately predict the duration of fast; however, threshold metabolite concentrations may still be useful for assessing whether periods of fasting in the wild are unusually long compared with those normally experienced.

abstract
1. Numbers of Steller sea lions Eumetopias jubatus in the North Pacific have declined. According to the Nutritional Stress Hypothesis, this decline is due to reduced food availability. Data from studies conducted on pinnipeds in the laboratory are used here to test whether the Nutritional Stress Hypothesis can explain the decline of Steller sea lions. 2. Overall, there is strong evidence for biologically meaningful differences in the nutritional quality of major prey species. Steller sea lions can partly compensate for low-quality prey by increasing their food consumption. 3. There appear to be no detrimental effects of low-lipid prey on sea lion growth or body composition when sea lions can consume sufficient quantities of prey. However, the ability to increase consumption is physiologically limited, particularly in young animals. Overall, it is more difficult to maintain energy intake on a diet of low-quality prey than on a normal diet. 4. Under conditions of inadequate food intake (either due to decreased prey availability or quality, or increased energy requirements) the overall impacts of nutritional stress are complex, and are dependent upon season, prey quality, age, and the duration and intensity of the nutritional stress event. 5. Studies on pinnipeds in the laboratory have been instrumental in identifying the conditions under which changes in sea lion prey can result in nutritional stress, and the nature of the physiological impacts of nutritional stress events.

abstract
We hypothesized that: (1) Steller sea lion Eumetopias jubatus diet choice is a function of prey availability, (2) sea lions move to take advantage of times and locations of seasonal prey concentrations and (3) the number present depends on the amount of prey available (numerical response). Over 3 yr, typically on a quarterly basis, in Frederick Sound, SE Alaska, multiple measurements were taken of Steller sea lion abundance (aerial surveys), diet (scats), dive behavior (satellite telemetry)and prey availability and caloric density (nearshore, pelagic and demersal fish surveys). We found that Steller sea lions shifted diet composition in response to changes in prey availability of pollock Theragra chalcogramma, hake Merluccius productus, herring Clupea pallasi and salmon Oncorhynchus spp. They selected intermediate-sized fish and avoided small (<10 cm) and large (>60 cm) fish, and moved between areas as prey became available seasonally. The number of sea lions present depended on the amount of prey available; a standing biomass of 500 to 1700 t of prey in a nonbreeding area such as Frederick Sound, depending on species composition, can attract and sustain about 500 sea lions. Pollock was more frequent in sea lion diet in inside waters of SE Alaska including Frederick Sound, Stephens Passage and Lynn Canal than anywhere else in Alaska and contributed about one-third of the dietary energy in Frederick Sound. This finding implies that a diet with substantial year-round contributions from less nutritious, but abundant prey such as pollock can form part of a healthy diet as long as more nutritious prey such as herring, salmon or eulachon Thaleichthys pacificus also are consumed. Our study supports the conclusion that the Steller sea lion is an opportunistic marine predator with a flexible foraging strategy that selects abundant, accessible prey and shifts among seasonally available species.

abstract
Changes in metabolic rates were measured in 3 captive female Steller sea lions (Eumetopias jubatus) that experienced fasts during summer and winter. Metabolic rates were measured (via O₂ consumption) before (MRs, surface) and after (DMR, dive + surface interval) the sea lions dove to 10–50 m depths. Measurements were obtained prior to 9-10 day fasts, and following a 14 day recovery period. The sea lions lost significantly more body mass (M_b) during the winter fast (10.6%), compared with the summer (9.5%). Mass-corrected dive metabolic rate (_cDMR = DMR • M_b^-0.714) was not affected by dive depth or duration, but increased significantly following the winter fasts (13.5 ± 8.1%), unlike the decrease during summer (-1.1 ± 3.2%). However, mass-corrected surface metabolic rate (_cMR_s) decreased significantly after both the summer (-16.4 ± 4.7%) and winter (-8.0 ± 9.0%) fasts. Consequently, the ratio between _cDMR and _cMR_c was significantly higher in winter, suggestive of an increased thermal challenge and convective heat loss while diving. Increased _cDM_s following the fast indicated that digestion began during foraging and was not deferred, implying that access to ingested energy was of higher priority than optimizing diving ability. _cDMR was elevated throughout the recovery period, independent of season, resulting in a 12% increase in foraging cost in winter and a 3% increase in summer. Our data suggest that Steller sea lions are more sensitive to changes in body condition due to food shortages in the winter compared with the summer.

abstract
Polymerase chain reaction techniques were developed and applied to identify DNA from >40 species of prey contained in fecal (scat) soft part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the Eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae and certain Gadidae). DNA identified 213 prey occurrences of which 75 (35%) were undetected by hard parts (mainly Salmonidae, Pleuronectidae, Elasmobranchii and Cephalopoda), and thereby increased species occurrences by 22% overall and species richness in 44% of cases (when comparing 110 scats that amplified prey DNA). Prey composition was identical within only 20% of scats. Overall, diet composition derived from both identification techniques combined did not differ significantly from hard part identification alone, suggesting that past scat-based diet studies have not missed major dietary components. However, significant differences in relative diet contributions across scats (as identified using the two techniques separately) reflect passage rate differences between hard and soft digesta material and highlight certain hypothesized limitations in conventional morphological-based methods (e.g., differences in resistance to digestion, hard part regurgitation, partial and secondary prey consumption), as well as potential technical issues (e.g., resolution of primer efficiency and sensitivity, and scat subsampling protocols). DNA analysis of salmon occurrence (from scat soft part matrix and 238 archived salmon hard parts) provided species-level taxonomic resolution that could not be obtained by morphological identification, and showed that Steller sea lions were primarily consuming pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Notably, DNA from Atlantic salmon (Salmo salar) that likely originated from a distant fish farm was also detected in two scats from one site in the Eastern Aleutian Islands. Overall, molecular techniques are valuable for identifying prey in the fecal remains of marine predators. Combining DNA and hard part identification will effectively alleviate certain predicted biases, and will ultimately enhance measures of diet richness, fisheries interactions (especially salmon related ones) and the ecological role of pinnipeds and other marine predators, to the benefit of marine wildlife conservationist and fisheries managers.

abstract
Marine mammal predator – prey interactions occur over different spatial and temporal scales, making it difficult to empirically decipher the influences they have on one another and on their ecosystems. However, their coexistence suggests that marine mammal predators and their prey have had profound influences on each other’s behaviors, physiologies, morphologies, and life-history strategies. The diversity of niches filled by marine mammals makes it difficult to generalize about the evolutionary consequences of their interactions with prey, beyond stating the obvious: marine mammals have adapted to catch food, while their prey have adapted to avoid being caught. On the shorter ecological time scale, marine mammals can affect the abundance of other species by consuming or outcompeting them. They can also indirectly affect the abundance of nontargeted species by consuming one of their predators, and can have strong impacts on the overall dynamics and structure of their ecosystems. One of the best tools for understanding marine mammal predator – prey interactions is the ecosystem model. However, more work is required through experimental manipulations and observational studies to evaluate the choices made by marine mammals and the costs of obtaining different species of prey.

abstract
Protected areas are often proposed as tools for conserving endangered populations of marine megafauna. Our study area includes a voluntary no-entry reserve embedded within wider critical habitat for Threatened ‘northern resident’ killer whales under Canada’s Species at Risk Act. Our study quantified the reserve’s importance to whales by assessing habitat preference in a behavioural context, and population-level implications of that preference given threats from human activities, such as oil spills resulting from shipping traffic. We recorded summertime activities of whales from 1995 to 2002. Whales were observed on 397 of 530 (74.9%) days. Whales showed strong preference for the reserve over adjacent waters, and used it preferentially for feeding and beach-rubbing. While the area comprises 0.001% of the whales’ range, an overall average of 6.5% of the population was present each day. Frequently, >50% of this small population was aggregated in the restricted and heavily trafficked waterway of Johnstone Strait. Using the Potential Biological Removal equation, we calculated potential annual mortality limits (ML) of 2.2 animals. Mean group size in the area exceeded ML on 55.8% of days overall, and 98.8% of days when conditioning on whale presence. The whales’ high reliance on a trivial fraction of their range means that opportunities are routine for one stochastic, catastrophic event to cause population decline. On 20 August 2007, a barge loaded with 10,000 L of diesel sank in the area, exposing 25% of the population. This underscores the importance of identifying critical habitat for threatened populations, and ensuring meaningful protection.

abstract
The physiology of free-ranging cetaceans is difficult to study and as a consequence, data on the energetics of these animals are limited. To better understand the energetic cost of swimming in killer whales, total cost of transport (COT) was estimated from swimming speeds and respiration rates from wild adult northern resident killer whales (Orcinus orca) and reported values of oxygen consumption in captive whales. Respiration rate (breaths per minute) was positively correlated with swimming speed (meters per second), while mass-specific COT (Joules per kilogram per meter) decreased with speed. Lack of data on very fast-swimming animals hindered assessment of the exact speed at which COT was minimal. However, minimum mass-specific COT for killer whales in the present study approached those predicted by a previously published allometric equation for marine mammals, and corresponded to “optimal” swimming speeds of 2.6–3 m/s. Interestingly, the observed average swimming speed (1.6 m/s) was lower than predicted optimal swimming speed. Finally, females with dependent calves had higher respiration rates than females without calves. These findings could be due to synchronous breathing with calves or could result from increased costs of lactation and swimming with a calf in echelon formation. Consequently, females with calves may have much greater COT at optimal swimming speeds than females without calves.

abstract
Top predators are often rare, subject to anthropogenic mortality, and possess life-history traits that make them inherently vulnerable to extinction. IUCN criteria recognise populations as Critically Endangered when abundance is <250 mature individuals, but estimating abundance of rare species can be more challenging than for common ones. Cost-effective methods are needed to provide robust abundance estimates. In marine environments, small boats are more widely accessible than large ships for researchers conducting sightings surveys with limited funds, but studies are needed into efficacy of small-boat surveys. This study compares line transect and mark-recapture estimates from small-boat surveys in summer 2004 and 2005 for ‘northern resident’ killer whales in British Columbia to true population size, known from censuses conducted by Fisheries and Oceans Canada. The line transect estimate of 195 animals (95% CI 27–559) used model averaging to incorporate uncertainty in the detection function, while the mark-recapture estimate of 239 animals (CI 154–370) used a simple two-sample Chapman estimator. Both methods produced estimates close to the true population size, which numbered 219 animals in 2004 and 235 in 2006, but both suffered from the small sample sizes and violations of some model assumptions that will vex most pilot studies of rare species. Initial abundance estimates from relatively low-cost surveys can be thought of as hypotheses to be tested as new data are collected. For species of conservation concern, any cost-effective attempt to estimate absolute abundance will assist status assessments, as long as estimates are presented with appropriate caveats.

abstract
We developed methods to estimate the spatial variation in economic values of ocean fisheries, and applied the methods to estimate the cost of closing groundfish fisheries in Steller sea lion Critical Habitat in the Bering Sea and Gulf of Alaska. The research addressed two related goals: (1) explicitly linking spatial variability of fisheries biomass and profitability over time to environmental variables; and (2) developing estimates of opportunity costs of time and area closures to the fishing industry at scales relevant to management. The approach involved two stages of statistical analyses. First, environmental conditions measured at 3 km and 9 km spatial scales and two-week and one-month intervals were used to predict fish biomass and fisheries catch per unit of effort (CPUE). Environmental variables included bathymetry, remotely sensed physical and biological observations, and output from a physical oceanographic circulation model. Second, we used predicted CPUE and spatial regulatory and cost factors to explain the spatial distribution of fishing effort over time. Our results suggested that 2001 Critical Habitat closures cost the North Pacific groundfish trawl fisheries 5-40 percent of their total potential net earnings. The improved methods for estimating opportunity costs of fisheries closures we present have direct applications to evaluating boundary changes to marine protected areas and other spatial management decisions. Limitations include the extensive data requirements and the need to bootstrap confidence intervals. If further research demonstrates the robustness and stability of the estimated relationships over time, the methods could project spatial fishery effects of climate variability and change, leading to dynamic spatial models linking fisheries with ecosystems.

abstract
Humpback whales were instrumented with satellite transmitters off the western Antarctic Peninsula in January of 2004-2006 to examine their movement patterns and habitat use. Whales were tracked from 4 to 80 days (mean = 36.5 days). Distance and travel rate estimates for nine individuals ranged from to 223 to 4,356 km and from 17 to 75 km/day, respectively. Considerable individual variation was observed in direction, speed and range of movements. The overall pattern was characterized by short- and long-distance movements between presumed foraging areas with relatively short residency times. Travel rates were lower at these sites, characterized by erratic movements, than during traveling between them. Area usage for six individuals based on the 95% fixed kernel home range with least squares cross-validation ranged from 2,771 to 172,356 km₂. The management boundary between the feeding grounds associated with Breeding Stocks G and A needs revision, as current available data suggest it should be located to the east of 50oW. This study is the first to present detailed information on the movements of humpback whales in the Southern Ocean.

abstract
In the Southwestern Atlantic Ocean, humpback whales migrate every winter to the Brazilian coast for breeding and calving in the Abrolhos Bank. This breeding stock represents the remnants of a larger population heavily exploited during the beginning of the 20th century. Despite its relevance to conservation efforts, the degree of current genetic variation and the migratory relationship with Antarctic feeding areas for this population are still largely unknown. To examine these questions, we sequenced *400 bp of the mitochondrial DNA control region from samples taken off the Brazilian coast (n = 171) and near the Antarctic Peninsula (n = 77). The genetic variability of the Brazilian humpback whale breeding population was high and similar to that found in other Southern Hemisphere breeding grounds. Phylogenetic analysis suggested the existence of a new mitochondrial clade that exists at low frequency among Southern Hemisphere populations. Direct comparison between the Brazilian and the Colombian breeding populations and the Antarctic Peninsula feeding population showed no genetic differentiation between this feeding region and the Colombian breeding area or between feeding Areas I and II near the Antarctic Peninsula. In contrast, these populations were genetically distinct from the Brazilian population. Two humpback whales sampled off South Georgia Islands, in the Scotia Sea, shared identical haplotypes to whales from Brazil. Our results, supported by photo-identification and satellite telemetry data, suggest that the main feeding area of the Southern Hemisphere humpback whale population is likely to be located near the South Georgia/South Sandwich Islands area and not in the Antarctic Peninsula.

abstract
The metabolic costs of foraging and the management of O₂ stores during breath-hold diving was investigated in three female Steller sea lions (Eumetopias jubatus) trained to dive between 10 and 50 m (n=1142 dives). Each trial consisted of 2 to 8 dives separated by surface intervals (SI) that were determined by the sea lion (spontaneous trials) or by the researcher (conditioned trials). During conditioned trials, SI was long enough for O₂ to return to pre-dive levels between each dive. The metabolic cost of each dive event (DMR = dive + surface interval) was measured using flow-through respirometry. The respiratory exchange ratio (VCO₂ ·VCO₂ ^-1) was significantly lower during spontaneous trials compared with conditioned trials. DMR was significantly higher during spontaneous trials and decreased exponentially with dive duration. A similar decrease in DMR was not as evident during conditioned trials. DMR could not be accurately estimated from the SI following individual dives that had short surface intervals (SI < 50 sec), but could be estimated on a dive by dive basis for longer SIs (SI > 50 sec). DMR decreased by 15%, but did not differ significantly from surface metabolic rates (MR_S) when dive duration increased from 1 to 7 min. Overall, these data suggest that DMR is almost the same as MR_S, and that Steller sea lions incur an O₂ debt during spontaneous diving that is not repaid until the end of the dive bout. This has important consequences in differentiating between the actual and ‘apparent’ metabolic rate during diving, and may explain some of the metabolic differences reported between pinniped species.