Estimation of Polar Bear Population Size and Survival in Western Hudson Bay

Abstract

Using Jolly-Seber mark-recapture models with data from 1977-92, we estimated size and survival rates of the polar bear (Ursus maritimus) population in western Hudson Bay to facilitate harvest management. Females fit mark-recapture models better than males. Population size showed no clear trend with estimates between 537 and 1,268 bears and a mean of 1,000 bears of all ages in autumn 1978-92. Mark-recapture estimates of survival for 1977-92 and 1987-89 data were 0.900 and 0.908 for females and 0.774 and 0.839 for males, respectively. Recruitment to the population in autumn averaged 191 cubs (SE = 10). The population was skewed toward females, which averaged 58% (SE = 2) of the population between 1978 and 1992. Mean age of both sexes increased over the study possibly because harvest quotas implemented in the 1960s limited harvest size and provided protection for females. Harvest levels appear sustainable for consumptive and nonconsumptive uses of the population. Given that the western Hudson Bay polar bear population was the most intensively studied in the world and that we had difficulty applying Jolly-Seber models to data for males, these models may not prove applicable to other polar bear populations unless large and unbiased samples are obtained