Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics

• Published in: Ecological Applications
• Main Authors: Rode, Karyn D., Taras, Brian D., Stricker, Craig A., Atwood, Todd C., Boucher, Nicole P., Durner, George M., Derocher, Andrew E., Richardson, Evan S., Cherry, Seth G., Quakenbush, Lori, Horstmann, Lara, Bromaghin, Jeffrey F.
• Other Authors: National Oceanic and Atmospheric Administration, National Science Foundation, Natural Sciences and Engineering Research Council of Canada, U.S. Bureau of Land Management, U.S. Geological Survey, Museum of the North, University of Alaska, Environment and Climate Change Canada, Canadian Wildlife Federation, U.S. Air Force, Bureau of Ocean Energy Management, Quark Expeditions
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2022
• Subjects: Arctic; Balaena mysticetus; Beaufort Sea; Beluga; Beluga*; Delphinapterus leucas; Pusa hispida; ringed seal; Sea ice; Ursus maritimus; Alaska
• Online Access: http://dx.doi.org/10.1002/eap.2751; https://onlinelibrary.wiley.com/doi/pdf/10.1002/eap.2751; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/eap.2751; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/eap.2751

Abstract Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator–prey interactions. Polar bears ( Ursus maritimus ) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under‐ice food web to meet its energy needs. In this study, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatiotemporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival (2004–2016), between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival, suggesting that concurrent increased dietary proportions of beluga whales ( Delphinapterus leucas ) did not offset reduced proportions of ringed seals ( Pusa hispida ). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free‐ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher‐fat diets than bears that summered on the pack ice, access to the remains of subsistence‐harvested bowhead whales ( Balaena mysticetus ) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year round, prey switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ...