Role of Diet and Food Intake Affecting Polar Bear Population Dynamics in Southern Beaufort Sea

This is a graphical abstract for a publication by the USGS and collaborators that examines the role of diet and food intake affecting polar bear population dynamics. Polar bears consume diets consisting of high proportions of marine mammal blubber that they access from the sea ice. When prey availability is low, polar bears are less selective consuming both the muscle and blubber of their prey whereas when prey are abundant, polar bears can selectively consume primarily blubber. This study used carbon and nitrogen isotopes to estimate the prey species and ratio of fat to protein in polar bears diets in the Northern Beaufort and Southern Beaufort Sea populations to better understand if bears can maintain high fat, high energy diets by prey switching when the abundance of their primary prey, ringed seals, is low. They found that bears in the western Beaufort Sea (Alaska) consumed the lowest proportions of dietary fat and ringed seal blubber during a period when polar bear abundance declined. Polar bears in the Northern Beaufort Sea population which has been stable over recent decades consumed higher proportions of ringed seals and dietary fat. Bears consuming less fat and lower energy densities would have to increase food intake from 2.1 to 3.0 kg/day in order to maintain energy intake. Prey-switching and consumption of whale carcasses onshore appeared insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Estimating dietary blubber using predator hair applied in the paper provides a new metric to monitor predator-prey relationships that affect individual health and population demographics. 

More information can be found in the following publication: 

Rode, K.D., B.D. Taras, C.A. Stricker, T.C. Atwood, N.P. Boucher, G.M. Durner, A.E. Derocher, E.S. Richardson, S.G. Cherry, L. Quakenbush, L. Horstmann, and J.F. Bromaghin. 2022. Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics.  Ecological Applications: https://doi.org/10.1002/eap.2751

Graphic by: Andres A. Aceves for USGS through the Virtual Student Federal Service program.