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Variability in polar bear (Ursus maritimus) stable isotopes in relation to environmental change in the Canadian Beaufort Sea

Nicole Boucher*, Andrew E. Derocher, Evan S. Richardson

*Corresponding author:

ABSTRACT: Diets of apex predators can be used to understand the effects of environmental changes within an ecosystem and to monitor shifts in community dynamics. Using δ15N and δ13C in polar bear (Ursus maritimus) guard hairs, we examined their diet in the Canadian Beaufort Sea from 2003 to 2011. We investigated how δ15N and δ13C were related to population demographics, sea-ice dynamics, climate indices, air temperatures, and ringed seal (Pusa hispida) ovulation rates. Bayesian stable isotope models were used to determine annual variation in prey contributions and niche widths. Diet contributions from ringed seal, bowhead whale (Balaena mysticetus), beluga (Delphinapterus leucas), and bearded seal (Erignathus barbatus) varied by sex, reproductive status, and year. Polar bear ringed seal consumption and niche widths were highest in 2004 following ringed seal reproductive failure in the early 2000s, and polar bear δ15N decreased when ringed seal ovulation rate was high. Polar bear δ15N and δ13C were linked to capture locations, which may reflect geographic gradients in stable isotopes within the Beaufort Sea. Climate indices were not related to polar bear δ15N and δ13C. Sea-ice dynamics were related to polar bear δ13C, suggesting that polar bear diets shift in response to environmental change. Overall, these results highlight the biological link between polar bears and ringed seals, as well as sea-ice dynamics, and the importance of considering geographic location in stable isotope studies.