NATIONAL PARK SERVICE Demography of Grizzly Bears in Relation to Hunting and Mining Development in Northwestern Alaska

Abstract. During 1986 through 1990, we permanently marked 146 grizzly bears (Ursus arctos); 67 were radio-collared within the Noatak River study area. Sex ratios of captured bears were not significantly different from 50:50. Average litter size at first observation was 2.17 (n = 35). Age of first reproduction ranged from 5 to 9 years of age. Fifty percent of first litters occurred at 5 years of age. Seventy-seven percent of the litters were weaned as 2.5-year-olds. Average interval between weaning was 3.9 years. Relations between sex and age and numerous physical measurements were examined.

We relocated 67 radio-collared bears from fixed-wing aircraft on 1,625 occasions. Use of slopes, aspects, and habitats varied by sex and age class. Home range sizes of males averaged 1,437 km², and for females the average was 993 km². Adult bears had high fidelity to the same area for denning, but individual den sites were not reused.

In 1988, six adult female bears were equipped with transmitters compatible with the Argos Data Collection and Location System and provided 1,865 relocations. Use of the mine garbage dump was documented with transmitters.

Density of adults (>3 years) was estimated by mark—recapture methods at 1/67 km² and at 1/50 km² for bears of all ages. The estimates were representative of high-quality denning habitat. Estimates for year-round habitat were much lower (1/69 km²).

Age structure of harvested male bears was skewed toward younger age classes, suggesting that the population was being heavily harvested. The age structure for captured females and harvested females was similar. Annual survival rates averaged 0.874 for cubs of the year (COY) and 0.887 for yearlings. Annual survival rates for adults older than 5 years averaged 0.906 for males and 0.940 for females. A large portion of the subsistence harvest (i.e., equal to or exceeding the sport harvest) is not reported. The large unreported harvest negates using harvest data to determine the status of the bear population.

Annual harvest rates ranged from 3.7 to 15.7% of the population from 1983 to 1989. Population modeling suggested a sustainable harvest of about 8%, whereas the literature suggested sustainable rates ranging from 2 to 6% annually. The bear population may be overexploited at existing harvest levels. Subsistence users have requested that hunting regulations be changed to accommodate their traditional practices and values. Any changes in the regulations should include mandatory reporting of the subsistence harvest to allow annual determination of population status.

Key words: Density, grizzly bear, harvest rates, mining development, mortality, population estimates, productivity, subsistence, satellite telemetry, Ursus arctos.