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

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 stable isotopes of nitrogen and carbon (delta N-15 and delta C-13) in polar bear Ursus maritimus guard hairs, we examined their diet in the Canadian Beaufort Sea from 2003 to 2011. We investigated how delta N-15 and delta C-13 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 was lowest and niche widths were highest in 2004 following ringed seal reproductive failure in the early 2000s, and polar bear delta N-15 decreased when ringed seal ovulation rate was high. Polar bear delta N-15 and delta C-13 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 delta N-15 and delta C-13. Sea ice dynamics were related to polar bear delta C-13, suggesting that the bears' 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.