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Bowhead whales MMRUBowhead whales feed year-round in Cumberland Sound, Nunavut

Satellite telemetry and time-depth recorders are providing new and surprising insights into the secret lives of bowhead whales

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A Window into the Lives of Resident Killer Whales

This summer, a team of researchers from the University of British Columbia, together with the Hakai Institute, set out to determine how fish-eating killer whales find their food, and whether there is a shortage of Chinook salmon available to killer whales in the Salish Sea.  Here is a peek into what the researchers saw.


Growth and development of North Pacific gray whales (Eschrichtius robustus).
Agbayani, S., S.M.E. Fortune and A.W. Trites. 2020.
Journal of Mammalogy, DOI:10.1093/jmammal/gyaa028
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
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Seasonal diving and foraging behaviour of Eastern Canada-West Greenland bowhead whales.
Fortune, S. M. E., S. H. Ferguson, A. W. Trites, B. LeBlanc, V. LeMay, J. M. Hudson and M. F. Baumgartner. 2020.
Marine Ecology Progress Series 643:197-217.
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.
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Predation by Pacific great blue herons on juvenile salmon.
Sherker, Z.T. 2020.
In Zoology. M.Sc. Thesis, University of British Columbia, Vancouver. 68 pages
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.
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