ASPECTS OF SURVIVAL IN JUVENILE POLAR BEARS

We captured, weighed, tagged, and monitored polar bear (Ursus maritimu s) cubs and yearlings in western Hudson Bay to examine survival rates and correlates with survival. Cub survival between spring and autumn i ncreased with cub mass and maternal mass, but was not related to mater nal age or maternal condition. Cub survival between spring and autumn varied annually between 39.0 and 100.0% and averaged 53.2%. Whole-litt er loss between spring and autumn was 30.8%, and only 38.0% of the fem ales did not lose any cubs. Survival of spring twins was similar regar dless of size, but in triplet litters, survival between spring and aut umn varied according to cub size. Minimum cub survival from one autumn to the next was 34.7% and was related to Cub mass, maternal mass, and maternal condition. Cub survival during autumn was estimated at 83.0% . Survival during the first year of life was no more than 44.0% but we could not estimate an annual survival rate because of the sampling re gime. Possibly because harvesting was the major mortality factor for y earlings (19.4% of the yearlings were removed from the population per year), no factors examined correlated with survival of yearlings. We f ound no sex-related differences in survival of cubs or yearlings in an y period. Relationships between survival in polar bear cubs and their condition suggest that lack of food availability, sometimes due to low maternal fat stores for lactation, leads to starvation and may be the main cause of mortality.