Habitat use and trophic ecology of the world’s rarest whale population on a rapidly warming subarctic foraging ground

Historical commercial whaling has drastically reduced North Pacific right whale (NPRW) Eubalaena japonica populations, impeding our ecological understanding and highlighting the challenges of studying species impacted before scientific research began. The warming subarctic Bering Sea is the core summer feeding ground for the Critically Endangered eastern population of NPRW, yet knowledge about the species’ foraging ecology as well as distribution during other seasons remains scarce. By modeling isotope values of NPRW skin, we revealed spring distribution and physiological responses of NPRW to ocean warming and sea ice retreat. Our findings confirm that NPRW are secondary consumers and indicate that the remnant population primarily feeds in the coastal Gulf of Alaska and Pacific subarctic gyres in spring, aligning with historical records. Joint attribute modeling of whale amino acid isotope values demonstrates their ability to track baseline environmental shifts. Moreover, we observed evidence for changes in NPRW physiology and habitat use related to sea ice, including feeding north of the whales’ Critical Habitat. These insights can inform recovery strategies for the NPRW, and the methodologies are translatable to other rare species as environmental conditions rapidly change.