Demography of polar bears : population projection, environmental change and public policy

Polar bears rely on sea ice for hunting their primary prey, seals. Global warming is causing reductions in Arctic sea ice, and concern has arisen about the demographic consequences for polar bears. I will report on a demographic analysis of the polar bear population in the southern Beaufort Sea. The analysis uses a female-dominant stage-classified matrix population model in which individuals are classified by age and breeding status. Parameters were estimated from capture-recapture data collected from 2001 to 2006. The results show that deterministic growth rates are affected by sea ice conditions, and that stochastic projections (both long-term and transient) are affected by the frequency of years with low ice conditions. When linked to forecasts of sea ice from global climate models, the results point to drastic population declines by the end of the 21st century. The polar bear is being considered for listing as a "threatened species" under the US Endangered Species Act, and this policy decision relies on demographic information.