abstract
Eastern North Pacific grey whales (Eschrichtius robustus) rely on energy obtained from Arctic feeding grounds to complete their 15,000-20,000 km annual round-trip migration between feeding and breeding areas. However, quantitative estimates of their food requirements remain scarce. Using an age-structured bioenergetics model incorporating life cycle stages and migration timings, we estimated daily energy needs across life stages. We found females need to supply nursing calves with 24–35 L of milk per day for 9-10 months. After weaning, juveniles require ~400 kg per day of Arctic amphipods (~5.6% of body weight), while the largest adults need a minimum of ~1,000 kg per day (~5.4%) during the 154-day summer foraging period. In contrast, pregnant females need 1,600–1,900 kg of prey per day (~9%–10%) to support fetal growth and store sufficient energy to produce milk while fasting and travelling northbound after calving in Mexico. Upon returning to their Arctic feeding grounds, lactating females require 1,300–1,600 kg of prey per day (7.9%–8.6%) for another 3.6 months to support the high costs of milk production. These estimates provide a quantitative framework for assessing how changes in Arctic prey availability can affect gray whale health, fitness, reproductive success, and population trends.

abstract
Estimating population parameters is crucial for understanding species dynamics and assessing anthropogenic impacts, thereby supporting conservation efforts. We evaluate key population parameters—group structure, abundance and capture–recapture probabilities—of the Guiana dolphin in the Paranaguá Estuarine Complex and adjacent coastal waters, southern Brazil. During 2021, we conducted 40 boat surveys to collect group structure and photo-identification data for mark–recapture modelling. We sighted 317 dolphin groups, with calves present in 56% of them. Group sizes ranged from 1 to 50 individuals, including aggregations of ~100–150 dolphins in Paranaguá Bay. We identified a total of 518 individuals and estimated the abundance of Guiana dolphins using two different programs, given the sparse nature of our dataset. The programme CAPTURE estimated N = 3770 (95% CI = 2591–5483; CV = 0.19), and Program MARK estimated N = 3087 (95% CI = 2072–4599; CV = 0.21) individuals, representing the largest Guiana dolphin population reported along the species' range. Capture probabilities varied seasonally, being lower during the wet season and higher during the dry season, consistent with greater numbers of identified individuals, larger group sizes and higher calf presence during the dry season. These results highlight the influence of environmental variability on habitat use and population dynamics and underscore the importance of long-term monitoring to understand population structure, movement patterns and anthropogenic impacts. Our findings emphasize that both biological and methodological factors must be considered when interpreting abundance estimates and that standardized approaches are essential for reliable comparisons across populations.

abstract
The American manatee (Trichechus manatus) requires freshwater mainly from rivers and springs to maintain osmoregulatory balance in saline environments. However, in Brazil's semi- arid Potiguar Basin, manatees now rely solely on submarine fresh-water springs because hypersaline estuaries have become unsuitable sources of freshwater. We applied MaxEnt modeling to presence- only data (sightings and filtered telemetry records) to produce habitat suitability maps and identify the environmental conditions driving habitat use. Telemetry locations were spatially and temporally thinned and subsampled to balance individual contributions, and alternative thinning scenarios were evaluated—while the model with the lowest level of spatial filtering showing the most stable performance was retained for inference. Model performance and fit were high (AUC = 0.979; CBI = 0.943, training gain = 2.76), and model suitability was strongly structured by proximity to submarine springs, with predicted probability declining sharply beyond 4–8 km. Seagrass presence contributed secondarily to suitability, whereas the other variables showed limited independent explanatory power at the regional scale. Suitable habitat was highly localized, comprising approximately 4% (301 km2) of the modeled coastal area and concentrated near Icapuí (Ceará) and Areia Branca (Rio Grande do Norte). These findings reveal the strong ecological constraints shaping this fully marine manatee population and highlight the critical role of submarine freshwater springs and seagrass meadows in sustaining manatee presence in hypersaline coastal systems. Protecting these key resources is essential for conservation planning in a region facing increasing freshwater limitation and expanding offshore development.

abstract
In the absence of sightings, stranding records can be used to parameterize habitat models for marine mammal conservation. However, their reliability for identifying suitable habitat remains uncertain. We assessed how stranding data influence the habitat predictions for American manatee (Trichechus manatus) in the Potiguar Basin, Brazil. Using MaxEnt, we compared models built using: (1) sightings and telemetry data, (2) stranding records alone, and (3) all three data sources combined. We found that the first model based solely on sightings and telemetry produced the most accurate and ecologically meaningful predictions. In contrast, the stranding- only model overestimated suitable habitat by more than threefold, while the combined model overpredicted it by more than twofold. These differences between model predictions are best explained by carcass drift and detection biases and indicate that stranding locations do not reliably reflect areas of actual habitat use. This quantitative assessment provides new insights into the significant biases stranding data can introduce into habitat suitability models. Our findings also highlight the need to prioritize direct observations, and to apply drift modeling and validation against direct observations when using stranding data, to ensure accurate and actionable conservation planning.

abstract
Arctic seals live in dynamic environments characterized by the seasonal advancement and retreat of sea ice. These amphibious marine mammals rely on sea ice as a haul-out substrate for rest and key life-history events, but they spend the majority of their time in the water. Current and predicted sea ice loss highlights the importance of estimating the costs of in-water activities when modelling the energy budgets of free-ranging seals under changing conditions. Yet, activity-specific costs are not available for many affected species. We used open-flow respirometry to measure and compare resting metabolic rates with the energetic costs of submerged diving and swimming in spotted (Phoca largha; n = 3), ringed (Pusa hispida; n = 1) and bearded seals (Erignathus barbatus; n = 1). Individuals were trained to voluntarily complete a sustained stationary breath hold under water or a continuous submerged swim before surfacing in a metabolic dome to measure rate of oxygen consumption. Metabolic rates decreased 11–24% relative to resting metabolic rate for the spotted and ringed seals while diving for 3, 5, or 7 min and did not change with increasing duration. The bearded seal did not show a similar decrease in diving metabolism. All individuals exhibited notable energetic increases to support exercise underwater while swimming at preferred speeds for 2–3 min. Metabolic costs were 243% and 114% above resting levels for spotted and ringed seals, but only 60% greater for the bearded seal. These results reveal the conflicting physiological responses of metabolic suppression while submerged (i.e. dive response) with the oxygen requirements of active swimming (i.e. exercise response) in Arctic seals and highlight the unique physiology of the bearded seal. The cost of submerged activities can now be considered in quantitative models of ice seal energy budgets, improving understanding of how physiological differences influence species-specific tolerance or vulnerability to rapidly changing Arctic conditions.

abstract
Habitat selection is a fundamental aspect of animal movement and behaviour, involving strategies that influence population regulation, species interactions, community structure and the generation and preservation of biodiversity. The Greater Caribbean Manatee is a megaherbivorous aquatic mammal with high environmental plasticity, found in a variety of coastal-marine ecosystems from the United States to Brazil. The subspecies is locally threatened because of intense poaching in recent centuries, which has led to the disruption of small populations. In this study, we aimed to understand habitat selection patterns and their variation across study sites, sex, age classes and between captive-released and wild manatees in northeastern Brazil to inform conservation policy. We used high-resolution GPS telemetry data from 20 tagged manatees and applied autocorrelation-informed resource selection functions (RSF) using (i) seagrass meadows, (ii) coral reefs, (iii) estuaries and (iv) freshwater springs as environmental predictors. As a proxy for anthropogenic impact, we also used a predictor combining multiple human activities at sea, which imposes substantial pressures with a subsequent degradation of manatee habitat. All environmental predictors had statistically significant results at the population level. Positive estimates were found for estuaries (1.52), springs (0.85) and seagrass meadows (0.77), indicating that manatees hierarchically select these habitats. The human impact was also positive (1.12), suggesting that the habitats selected by manatees overlap with human-impacted areas. Coral reefs (−0.92) were found to have a negative estimate, indicating that the animals avoid using this habitat. Our results confirm the vital role of seagrass meadows and freshwater in manatee movement behaviour. The selected habitats overlap with human-impacted areas, particularly in areas close to urban centers and ports. This creates obstacles to manatee free movement and the reconnection of subpopulations, highlighting the importance of conserving and restoring these marine coastal habitats.

abstract
Assessing the vulnerability of species to global climate change and their capacity for resilience is a central challenge in ecology. Responses are variable and difficult to predict but understanding the resilience of intrinsically vulnerable species is necessary for management of natural populations. Bowhead whales (Balaena mysticetus) have recovered from historical over-exploitation in several Arctic regions. However, the East Greenland-Svalbard-Barents Sea (EGSB) population remains endangered, with little known about their habitat use, foraging ecology, or potential resilience. We analysed location data from 38 EGSB bowhead whales instrumented between 2017 and 2021. We performed home range analyses, fitted a modified resource selection function, and estimated move persistence to assess the influence of environmental conditions on movement patterns using linear mixed-effects modelling. EGSB bowheads used an offshore, deep-water core area year-round. Movement patterns showed considerable individual variability and suggest this population is not migratory in a classical sense, likely reducing intraspecific competition. Depth, low sea surface temperatures, and sea ice were all influential on habitat use. Both static and dynamic environmental conditions were significantly associated with apparent foraging behaviour. Although the habitat use of EGSB bowhead whales is vulnerable to continued warming, intrapopulation variability in movements might provide a buffer to climate change.

abstract
Per- and polyfluoroalkyl substances (PFAS) are thousands of toxic synthetic chemicals that bioaccumulate and persist in the environment. They are known to cause immunotoxicity, organ damage, endocrine disruption, and reproductive impairments in wildlife such as sea otters (Enhydra lutris). However, there is limited information on the distribution of these chemicals across the Northeastern Pacific, and baseline data are missing to assess their potential impacts on sea otters in regions such as British Columbia (BC), Canada. We analyzed liver (n=11) and skeletal muscle samples (n=5) from 11 deceased sea otters from coastal BC using the EPA method 1633 with UPLC-MS/MS. We found 8 of the 40 tested PFAS were present in all sampled sea otters, although concentrations of each PFAS varied between individuals. Sea otter livers contained more PFAS compounds at higher total average concentrations than skeletal muscle (i.e., 8 PFAS totaling 10.48 ng/g ww vs. 1 PFAS totaling 0.38 ng/g ww). Only PFOSA was identified in both liver and muscle tissues, while the remaining 7 PFAS were unique to the liver. The three PFAS that dominated the liver PFAS composition (PFNA, PFOSA, and PFOS) accounted for 84% of the contaminant load in the livers. Geographically, PFAS concentrations were over 3 times higher on average in sea otters recovered near major cities and shipping routes. Identifying the contaminants accumulating in sea otters provides insights into the health threats confronted by recovering sea otter populations. Our study also establishes baseline PFAS contamination levels in BC sea otters, which can be used to monitor and regulate the presence of PFAS on marine environments in western Canada.

abstract
As breath‐hold divers, marine mammals must coordinate their use of both aerobic and anaerobic metabolism to maximize their time at depth. One indication of the relative reliance between these two energy‐producing systems is the aerobic dive limit (ADL), defined as the dive duration where post‐dive blood lactate concentrations surpass resting levels. Both the timing of the ADL and ensuing rate of lactate accumulation can affect subsequent diving behavior. Despite its importance as a physiological benchmark in diving physiology, the ADL is rarely measured directly. This study investigated the relative reliance on aerobic and anaerobic metabolism in freely diving Steller sea lions (Eumetopias jubatus) by measuring post‐dive lactate concentrations and oxygen and carbon dioxide recovery times in relation to dive duration. The rapid onset of elevated post‐dive lactate concentrations suggests that Steller sea lions rely on anaerobic metabolism even for dives with relatively short durations. Further, relative decreases in oxygen recovery times with increasing dive durations are consistent with a downregulation of aerobic metabolism during longer periods of submergence. These findings offer new insights into the metabolic strategies employed by Steller sea lions and could inform the development of physiologically‐based optimal foraging models.

abstract
West Coast Transient (WCT) killer whales (Orcinus orca rectipinnus) hunt marine mammals along the west coast of North America from California to southeastern Alaska. However, little information is available on their seasonal use of nearshore areas and the relative importance of different parts of their range. Using sighting data from 2016 to 2023, we assessed their seasonal distribution and abundance in the inside waters of Vancouver Island (the Salish Sea and North Island Waters). WCT killer whales were seen an average of 250 days throughout each year. They were most frequently observed in the Salish Sea from March to September but had fewer sightings in July of even years when pink salmon returns were low. In contrast, occurrences of WCT killer whales in the North Island Waters peaked in September but were significantly lower overall. Peak occurrences in both areas corresponded with the seasonal presence of seals and sea lions, their primary prey. Overall, ~70% of the coastal subset of the WCT population occurred annually in a region that accounts for a relatively small portion of their range. This high concentration highlights the importance of the inside waters for their survival and emphasizes the need to assess other key areas within their range.

abstract
Lowering heart rate while diving helps marine mammals regulate blood pressure while redistributing blood flow and conserving oxygen during extended dives. However, the classic characterization of this dive response—as a pronounced and abrupt reduction in heart rate observed during forced dives in laboratory settings—contrasts with the higher minimum heart rates and oscillatory patterns observed in freely diving marine mammals in the wild. To assess this apparent discrepancy in cardiovascular control, we measured the heart rates of three Steller sea lions (Eumetopias jubatus) using subcutaneous cardiac monitors during trained stationary dives (3–4 m) in an aquarium pool. During 12 of the longest dives (76–161 s), heart rates decreased from an average 95 to 34 bpm within the first 26 seconds of submergence. However, while mean HR at depth eventually averaged around 31 bpm, it also oscillated between 27–39 bpm every ~5–6 seconds (0.2 Hz) for much of the dive, before rising prior to surfacing. The observed relatively slow drops in heart rates were similar to other marine mammals, suggesting an optimal rate of declining heart rates that reflect the anticipated conditions of voluntary dives. We further hypothesize that the oscillating minimum heart rates of freely diving marine mammals reflect time delays in the baroreceptor reflex due to the prolongation of circulation time. Our findings provide new ideas about how these delays shape the rate and pattern of heart rate decline, ultimately influencing cardiovascular control, gas management and breath-hold duration in diving mammals.