2001b. Polar bears in the Beaufort Sea: A 30-year mark-recapture case history

• Main Authors: S. C. Amstrup, T. L. Mcdonald, I. Stirling
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Beaufort Sea; Ursus maritimus
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.600.8465; http://www.west-inc.com/reports/big_game/Amstrup et al 2001.pdf

Knowledge of population size and trend is necessary to manage anthropogenic risks to polar bears (Ursus maritimus). Despite capturing over 1,025 females between 1967 and 1998, previously calculated estimates of the size of the southern Beaufort Sea (SBS) population have been unreliable. We improved estimates of numbers of polar bears by modelingheterogeneityin captureprobabilitywith covariates.Importantcovariatesreferred to the year of the study, age of the bear, capture effort, and geographic location.Our choice of best approximating model was based on the inverse relationship between variance in parameter estimates and likelihood of the t and suggested a growth from ~ 500 to over 1,000 females during this study. The mean coef cient of variation on estimates for the last decadeof the studywas 0.16—the smallest yet derived.A similarmodel selectionapproach is recommendedfor other projectswhere a bestmodel is not identi ed by likelihoodcriteria alone. Key Words: Capture–recapture; Covariates; Logistic modeling; Population estimation. 1.