Survival rates of radio-collared female polar bears and their dependent young

Polar bears are hunted throughout most of their range. In addition to
hunting, polar bears of the Beaufort Sea region are exposed to mineral
and hydrocarbon extraction and related human activities such as
shipping, road building, and seismic testing. As human populations
increase and demands for polar bears and other arctic resources
escalate, reliable estimates of survivorship of polar bears are needed
to predict and manage the impacts of those activities. We used the
Kaplan-Meier model to estimate annual survival (with 95% confidence
intervals) for radio-collared female polar bears and their dependent
young that were followed during a 12-year study in the Alaskan
Beaufort Sea. Survival of adult female polar bears was higher than
had been previously thought: S = 0.969 (range 0.952-0.983). If
human-caused mortalities were deleted, the computed survival rate was
0.996 (0.990-1.002). Survival of young from den exit to weaning was
0.676 (0.634-0.701). Survival during the second year of life, 0.860
(0.751-0.903), was substantially higher than during the first year,
0.651 (0.610-0.675). Shooting by local hunters accounted for 85% of
the documented deaths of adult female polar bears. Conversely, 90% of
documented losses of young were independent of litter size (P = 0.36),
indicating that parental investment in single cubs was not different
from investment in litters of two or more. Precise estimates of the
survival of independent juveniles and adult males still need to be
developed.