Decadal migration timing and temporal variation in dive behavior of an endangered beluga whale population

IntroductionUnderstanding migration timing and movement behavior is critical for predicting population responses to environmental changes. The beluga whale (Delphinapterus leucas) population in Cumberland Sound, Nunavut, is currently endangered due to historical and ongoing overharvesting.MethodsBy comparing satellite telemetry data from two distinct time periods (1998–1999 and 2006–2008), we evaluated beluga whale dive behavior and migration timing in relation to environmental and seasonal factors. To infer potential prey shifts, we compared the proportion of dives deeper than 100 m, where Arctic cod (Boreogadus saida) are typically found, with shallower dives indicative of capelin (Mallotus villosus) foraging. Dive behavior was analyzed in relation to seasonal progression (day of year), time period, ice cover, bottom depth, and sex using mixed-effects models. Migration timing was evaluated using latitudinal thresholds and a transect line to identify the timing and variability of southward autumn movements relative to sea ice formation.ResultsWe found significant seasonal (day of year) variation in dive behavior, with deep dives increasing from September to December. Additionally, there was a notable shift to more shallow dives in the second time period compared to the first, suggesting a change in foraging from Arctic cod to capelin. We found that the whales’ initial movements out of their summering area appeared largely independent of ice phenology, while their movements later in their migration were highly variable.DiscussionThe shift in prey likely occurred due to changes in prey distribution driven by warmer ocean temperatures, which may have negative long-term impacts on population health. Some of these behavioral trends contrasted with those of other beluga whale populations, emphasizing the need for population-specific management strategies to support long-term survival of the Cumberland Sound beluga whale population.