Polar bears in the Beaufort Sea: A 30-year mark-recapture case history

Knowledge of population size and trend is necessary to manage anthropogenic risks to polar bears (Ursus maritimus). Despite capturing over 1,025 femal es between 1967 and 1998, previously calculated estimates of the size of th e southern Beaufort Sea (SBS) population have been unreliable. We improved estimates of numbers of polar bears by modeling heterogeneity in capture pr obability with covariates. Important covariates referred to the year of the study, age of the bear, capture effort, and geographic location. Our choic e of best approximating model was based on the inverse relationship between variance in parameter estimates and likelihood of the fit and suggested a growth from similar to 500 to over 1,000 females during this study. The mea n coefficient of variation on estimates for the last decade of the study wa s 0.16- the smallest yet derived. A similar model selection approach is rec ommended for other projects where a best model is not identified by likelih ood criteria alone.