Abstract
Polar bears (Ursus maritimus) rely on sea ice for hunting marine mammal prey. Declining sea ice conditions associated with climate warming have negatively affected polar bears, especially in the southern portion of their range. At higher latitudes, the transition from multi-year ice to thinner annual ice has been hypothesized to increase biological productivity and potentially improve polar bear foraging conditions. To investigate this possibility, we used quantitative fatty acid signature analysis to characterize the diet composition of 148 polar bears in two high-latitude subpopulations from 2012 to 2014: (1) Viscount Melville Sound, where little is known about marine mammal ecology, and (2) Northern Beaufort Sea, a subpopulation considered stable with comparatively more ecological data. We used adipose tissue lipid content as an index of body condition. To characterize long-term habitat conditions, we examined trends in sea ice metrics from 1979 to 2014 in both regions. Although the diets of bears in both subpopulations were dominated by ringed seal (Pusa hispida, mean biomass consumption = 45%), bears in Viscount Melville Sound showed higher proportional consumption of beluga whale (Delphinapterus leucas; mean biomass consumption = 37%) than any other polar bear subpopulation studied to date. Although the three-year duration of our study precludes long-term insights, relatively lighter sea ice conditions in Viscount Melville Sound were associated with reduced consumption of preferred prey (i.e., ringed seal), especially among female polar bears. Further, polar bears in Viscount Melville sound were in poorer body condition than those in the Northern Beaufort Sea. Our results do not indicate that declining sea ice has had any positive effect on polar bear foraging at high-latitudes.
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Acknowledgements
We are particularly grateful to the Inuvialuit Game Council and Inuvialuit hunters for collecting adipose tissue samples from polar bears harvested during their subsistence hunts. Thanks to the researchers, field assistants, and helicopter personnel that assisted in the safe capture and handling of polar bears. We are thankful for financial support from Natural Sciences and Engineering Research Council (NSERC) Discovery Grant, Kenneth M. Molson Foundation, Environment and Climate Change Canada, Northern Scientific Training Program, Nunavut Wildlife Management Board Nunavut Wildlife Research Trust, Government of the Northwest Territories, Polar Continental Shelf Program, Inuvialuit Implementation Funds, World Wildlife Fund, and York University, Faculty of Graduate Studies. We thank Marsha Branigan and Jodie Pongracz (Government of Northwest Territories) for organizing and facilitating sample collection and providing ecological insights on the Beaufort Sea ecosystem. We thank D. McGeachy (Environment and Climate Change Canada) for a summary analysis of sea ice metrics, S. Budge and C. Barry (Dalhousie University) for conducting gas chromatography, L. Harwood (Fisheries and Oceans Canada) and J. Alikamik for ringed seal adipose tissue samples, and S. Ferguson (Fisheries and Oceans Canada) and J. Higdon (Higdon Wildlife Consulting) for access to beluga entrapment reports. We thank L. Adams, A. Fischbach (USGS Alaska Science Center), A. Derocher (University of Alberta), R. Dietz (Aarhus University) and two anonymous reviewers for their helpful comments on an earlier version of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not constitute endorsement by the U.S. Government. This article is a U.S. Government work and is in the public domain in the U.S.A. This article was reviewed and approved under the U.S. Geological Survey, Fundamental Science Practices policy (http://www.usgs.gov/fsp).
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KRNF and GWT conceived and formulated the ideas, ESR provided data, KRNF processed tissue samples, KRNF and JFB analysed the data, KRNF and GWT wrote the manuscript, and JFB and ESR provided editorial advice and ecological insights.
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Florko, K.R.N., Thiemann, G.W., Bromaghin, J.F. et al. Diet composition and body condition of polar bears (Ursus maritimus) in relation to sea ice habitat in the Canadian High Arctic. Polar Biol 44, 1445–1456 (2021). https://doi.org/10.1007/s00300-021-02891-8
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DOI: https://doi.org/10.1007/s00300-021-02891-8