Population Characteristics of Alaskan Polar Bears

A mark-recapture study of Alaskan polar bears (Ursus maritimus) was conducted between 1967 and 1976. Of 809 bears tagged, 147 were recaptured 1 or more times or killed by hunters. Three-year-old males and 6- and 7-year-old females were underrepresented in the captured sample. Analyses of cohort age composition over time indicated male (age 6+) and female (age 8+) annual survival rate of 0.84. Average litter size was 1.63 and breeding interval was 3.6 years. The age of first successful breeding for females was 5.4 years. For adult females, the average number of young per year was 0.45. With these fecundity estimates, the annual juvenile survival rate of 0.97 calculated from cohort data is that which is required to maintain population size.