Individuals matter: investigating individual-level foraging variability in Eastern Canada-West Greenland bowhead whales (Balaena mysticetus)

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Pontbriand, Tommy
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The main objective of my thesis was to assess the individual-level foraging variability of Eastern Canada-West Greenland (EC-WG) bowhead whales under climate-driven changes in prey. Specifically, I tested two mechanisms potentially responsible for explaining inter-individual diet variation: foraging behaviour (i.e., habitat use and foraging dive depth), and individual specialization. First, I found that bowhead whale individuals using distinct summer and fall foraging habitats displayed differences in horizontal movements, foraging dive depth and dietary biomarkers. Individuals using the Canadian Arctic Archipelago habitat (Foxe Basin, Gulf of Boothia, Prince Regent Inlet, Lancaster Sound and Admiralty Inlet, Nunavut) performed long distance movements across regions, and their foraging dive depth was generally shallow, but increased from July to November. These whales displayed higher δ13C and δ15N values and ratios of C16:1n7/C16:0 than individuals using the West Baffin Bay habitat (Cumberland Sound, Baffin Bay, Davis Strait), which were more localized in their horizontal movements and consistent over time in their foraging dive depth, which was generally deeper. Second, I found that individual specialization did not seem to be an important mechanism increasing population-level isotopic niche variation, as most of the remaining δ13C and δ15N variation unaccounted for by the fixed effects was attributed to intra-individual variation (79% and 67%, respectively). This isotopic variation within individuals was associated with seasonal migrations between isotopically distinct habitats and variable food intake that cause the yearly isotopic cycles observed in baleen plates. Year was the best predictor of both carbon and nitrogen isotope ratios and drove most of the downward long-term trends in both δ13C and δ15N values, likely due to changes in baseline isotopic ratios and/or a possible shift in the feeding ecology of the population. The results from this chapter showed a wide isotopic variability within individuals suggesting broad overlapping niche breadths and individual-level plasticity. Overall, the observed individual-level variation in habitat use, foraging dive depth and dietary biomarker (i.e., stable isotopes and fatty acids) within the EC-WG bowhead whale population suggests high individual-level ecological plasticity which would increase the resilience of the population against changing habitats and prey.
Bowhead whales, Stable isotopes, Fatty acids, Foraging behaviour, Diet, Satellite telemetry, Individual specialization, Climate change