Movements, distribution, and population dynamics of polar bears in the Beaufort Sea

Abstract

I used mark and recapture, and radio telemetry to describe movements and population dynamics of polar bears of the Beaufort Sea. Rates of movement were lowest for females with cubs in spring, highest for females with yearlings in winter, and varied from 0.30-0.96 km/h. Total distances moved each month and year were 186-492 km and 1,454-6,203 km respectively. Highest and lowest levels of activity were in June and September. Activity levels were highest from mid-day to late evening. Females with cubs were more active than other bears. Annual home ranges varied from 12,730 km$\sp2$ to 596,800 km$\sp2$. The Beaufort Sea population occupied a 939,153 km$\sp2$ area extending 300 km offshore from Cape Bathurst, Canada, to Pt. Hope, Alaska. Maternal denning in the Beaufort Sea region was common, but 52% of discovered dens were on the drifting pack ice. Bears denning on pack ice drifted as far as 997 km (x = 385 km). Bears followed to >1 den did not reuse sites. Consecutive dens were 20-1,304 km apart, but radio-collared bears were faithful to substrate and locale of previous dens. Of 44 polar bears that denned along the Beaufort Sea coast, 80% were located between 137$\sp\circ$00'W and 146$\sp\circ$59'W. Of those 44, 20 (45%) were on the Arctic National Wildlife Refuge, including 15 (34%) in the 1002 coastal plain area, which may contain >9 billion barrels of recoverable oil. Data indicated, however, that spatial and temporal restrictions on developments could prevent most disruptions of denned bears. Survival of adult female polar bears was higher than previously thought ($\ S=0.96).$ Survival of cubs ($\ S=0.65)$ and yearlings ($\ S=0.86)$ was lower than for adults, but increased rapidly with age. Shooting accounted for 85% of the documented deaths of adult females. The population grew to ~1500 animals ($\ge$2% per year) from 1967-1992. Condition of adult females, survival of young, and litter sizes declined, while age of maturity and reproductive interval appeared to increase. The population may have approached carrying capacity by the end of the study.