Arctic sea-ice variability is linked to long-term changes in bowhead whale foraging.

Environmental variability can restructure prey fields, shifting predator foraging across space and time. In the rapidly changing Arctic, sea-ice loss is altering prey availability, yet its long-term consequences for marine predators remain unclear. We combined multi-decadal baleen isotope records with satellite-derived sea-ice data to assess how interannual variation in sea-ice area across the Bering, Chukchi, and Beaufort Seas is associated with annual baleen isotopes and isotopic niche width in Bering-Chukchi-Beaufort bowhead whales (Balaena mysticetus). Using 2755 baleen segments from 25 mature whales, we reconstructed isotopic records spanning 1988-2022 and integrated bulk δ13C with essential amino acid δ13C to distinguish changes in foraging ecology from long-term shifts in isotopic baselines. Annual baleen δ13C was most strongly associated with variation in sea-ice area in the Bering and Beaufort Seas, whereas baleen δ15N was associated with sea-ice area in the Bering Sea, suggesting that regional sea-ice variability influences the relative contribution of prey sources assimilated across isotopically distinct foraging regions throughout the annual migration. Consistent with these patterns, reduced sea-ice conditions in the Chukchi and Beaufort Sea were associated with broader individual isotopic niches, whereas total niche width increased under reduced Beaufort Sea ice. Together, our results suggest that bowheads respond to Arctic sea-ice variability through adjustments in resource use across the Pacific Arctic, a behavioral flexibility that may contribute to resilience under continued Arctic change, although continued monitoring will be essential to determine whether this potential capacity can be sustained under future conditions.