Assessing Population Projections for Beaufort Sea Polar Bears
Sea ice allows polar bears to exploit their environment by providing a platform for hunting seals. The most preferred sea ice habitat occurs over the highly productive continental shelf. A reduction in the total amount of this optimal habitat may reduce polar bear populations. Photo: S. Amstrup, USGS
The polar bear is recognized worldwide as a vulnerable species due to global warming induced loss of its required sea ice habitats. USGS science played a central role in informing the 2008 decision by the Department of the Interior to list the polar bear as threatened under the Endangered Species Act. This science was founded in understanding gained from long-term studies of the southern Beaufort Sea (SB) population, one of 19 worldwide, and one of only two populations with long-term data. In these studies, USGS documented a negative relationship between length of the open water season over the continental shelf and population growth rate. Applying future sea ice conditions, as projected from climate models developed by the Intergovernmental Panel on Climate Change, to the relationship between sea ice availability and population growth rate allowed us to project a future trajectory of the population. In this current project supported by CLU R&D, we are monitoring the survival and habitat use of the SB population to determine (i) whether available habitat changes as projected and (ii) how observed changes influence population dynamics. Information about how polar bears in this population respond to sea ice loss will inform projections for the worldwide population.
Why is this research important?
The polar bear is a worldwide icon for the effects of climate warming. The Department of the Interiorís decision to list the polar bear as threatened was based on projected habitat loss due to climate warming in the 21st century. The Secretary of the Interior has made it a priority to refine the projection models as new empirical information is acquired to clarify and hopefully reduce the uncertainties associated with the decision at the time it was made. Information on the current and future status of the SB polar bear population is relevant to agencies that are responsible for polar bear conservation in Alaska (e.g., U.S. Fish and Wildlife Service, the Bureau of Land Management, the Bureau of Ocean Energy Management, State of Alaska, North Slope Borough, Inupiat-Inuvialiut Commission, Alaska Nanuuq Commission). The information is also used by the IUCN Polar Bear Specialistsí Group, which serves as Technical Advisor to the Polar Bear Range States (Norway, Canada, Russian, Greenland, U.S.). USGS findings that greenhouse gas mitigation can improve the outlook for the polar bears is relevant to ongoing discussions about polar bear conservation worldwide.