Effects of hunting on brown bear cub survival and litter size in Alaska

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Miller, S. D., R. A. Sellers, and J. A. Keay. 2003. Effects of hunting on brown bear cub survival and litter size in Alaska. Ursus 14(2):130-152.

ABSTRACT: We present data from 4 studies of radio-marked brown bears (Ursus arctos) in Alaska to evaluate the effects of hunting and differential removal of males on cub survival and litter size. In the Susitna area in south central Alaska, the proportion of males declined during a period of increasing hunting pressure (1980–96). Cub survivorship was higher in the heavily hunted Susitna population (0.67, n =167 cubs) than in a nearby unhunted population in Denali National Park (0.34, n = 88 cubs). On the Alaska Peninsula, in coastal areas rich in salmon (Oncorhynchus spp.) and with higher brown bear densities, cub survivorship was significantly higher in the hunted Black Lake population (0.57, n = 107 cubs) than in an unhunted population in Katmai National Park (0.34, n = 99 cubs). The Black Lake population had alternate-year hunting, and cub survivorship was similar during years with and without hunting during the preceding fall and spring. In both coastal and interior comparisons, litter sizes were either larger or not significantly different in hunted areas than in nearby unhunted national parks. We found no evidence that removal of adult male bears by hunters reduced cub survival or litter size. For populations below carrying capacity, convincing evidence is lacking for density dependent effects on cub survivorship or litter size. In our studies, variations in cub survivorship and litter size were best explained by proximity to carrying capacity; local environmental factors and stochastic events probably also influence these parameters. We believe that cub survivorship in our national park study areas was lower than in nearby hunted areas because of density-dependent responses to proximity to carrying capacity.