The population biology of polar bears occupying land in summer months is comparatively well known. Much less is known about the larger fraction of polar bear populations which stays on the ice through the summer. A better understanding of the physiology of fasting in both summer habitats is needed to understand how reduced sea ice cover in the Arctic will impact polar bear populations. Bears that stay ashore in summer have almost no access to food and tend to be inactive. Those that stay on the ice, however, have continued access to prey and make extensive movements. This project pairs scientists from the University of Wyoming and the U. S. Geological Service to follow the movements of bears in both habitats and monitor their body temperature, muscle condition, blood chemistry, and metabolism. They will determine the physiological implications of summering on the ice versus on shore. The physiological data will be added to spatially-explicit individual-based population models to predict population response to reduced ice cover. The results will provide information important to management by indigenous, U.S., and international management and conservation agencies and address the interests of policy makers and the public.
Principle Investigators: Henry Harlow and Merav Ben-David Graduate Student: John Whiteman Collaborators: Steven Amstrup (USGS and PBI); George Durner, Anthony Pagano, Elizabeth Peacock, Karyn Rode, and Kristin Simac (USGS); Eric Regehr (USFWS), Geoff York (WWF). A large segment of the world’s polar bear (Ursus maritimus) population follows the retreating sea ice northward and spends much of the summer and early fall on the pack ice over deep-water. These individuals likely contend with different conditions than those experienced by bears that spend the summer on shore. We hypothesized that the cooler temperatures on the pack ice and potential opportunistic predation of ringed seals (Phoca hispida) may result in a higher activity and food intake, which could facilitate maintenance of fat and protein reserves in ice-bound bears. In contrast, bears that spend the summer on shore may be more food deprived and reduce their energetic expenditure by lowering activity and metabolic rates. Because the capacity of polar bears to withstand extended periods of food scarcity is finite, we expected that the ability of polar bears to remain on the pack ice year-round will minimize the negative effects of reduced foraging opportunities associated with declines in annual sea ice. If bears were able to maintain protein and lipid stores by foraging on the sea ice year-round they may be buffered from the ill effects of climate change. Nonetheless, the thinning of 1st year and multiyear ice contributes to the continued decline in the extent of sea ice in the Arctic. This phenomenon may eventually force all bears onto land resulting in loss of this physiological buffer. We designed this project to assess whether polar bears that follow the pack ice north of the continental shelf experience less food deprivation and are better able to maintain lipid and protein stores in comparison with land-bound bears. Between 2008 and 2010 we captured 110 individuals from both groups along the Alaskan coast of the Beaufort Sea before the ice-retreat period in the summer (April – August). We recaptured 29 of them on land, as well as on the pack ice (using the USCG Polar Sea as a floating base), shortly before the ice re-formed in fall (October). Using GPS satellite technology, activity sensors, temperature loggers, and by sampling blood, breath, and other tissues, we found that in contrast with our expectations, ice-bound bears may exhaust their lipid and protein stores during the ice-free period of fasting. Deteriorating sea ice conditions, which may increase incidents of swimming, could enhance the utilization of lipid and protein stores in these bears. In contrast, bears on shore appeared to maintain some lipid stores by the end of the fasting period. This unexpected result may be overshadowed by our finding that the Beaufort Sea bears experience more profound food deprivation while overwintering on ice over the continental shelf compared to summer, regardless of their habitat selection strategy. Together these observations may cause a paradigm shift in our understanding of polar bear ecology and could have significant influence on future management decisions. Five graduate students were involved in this project as well as 11 undergraduate students, including women and minorities. We also hosted a K-12 teacher as part of the Teachers Experiencing the Arctic and Antarctic Program (PolarTREC) and collaborated with the Exploratorium. We delivered 15 presentations to various audiences across the globe, 9 professional presentations in conferences, and hosted 3 open-house meetings in rural communities in Alaska. Over the course of the project, we submitted 7 permit applications and 16 progress reports and updates to the U.S. Fish and Wildlife Service, the University of Wyoming Animal Care and Use Committee, the North Slope Borough, Alaska, the governments of the Yukon and Northwest Territories in Canada, Oil Industry companies in Alaska, the U. S. State Department, the U. S. Coast Guard, Polar Bear International, World Wildlife Fund, UNOLS and the National Science Foundation. Dissemination of results also included collaboration with several media platforms including the National Geographic Society, Natural Exposures, and many writers. For more information and continued project updates please visit: http://uwyo.edu/polarbear/.
