Estimating Survival

Because polar bears are harvested in most areas and also increasingly exposed to other human perturbations, understanding the processes of reproduction and survival is essential. Estimating the numbers of cubs produced in polar bear populations can be logistically difficult, but is technically straightforward. Estimating survival, on the other hand, is both logistically and technically challenging. Making reasonable estimates of survival continues to provide a stumbling block for researchers and managers alike. Although estimates of survival derived from radiotelemetry studies are consistent with ecological theory (Amstrup and Durner 1995; Eberhardt 1985), the lack of concordance among estimates derived by different methods is troubling. The best estimates derived without the aid of telemetry (Derocher and Stirling 1995a; Lunn et al. 1997) are not in the range thought to be necessary to sustain populations (Eberhardt 1985). Also, telemetry estimates can be derived only for females because male polar bears will not retain radio-collars. As management needs intensify, precise estimates of survival of independent juvenile polar bears as well as adult males will need to be developed while survival patterns of females and dependent young are reevaluated.