Estimating Grizzly Bear Density in Relation to Development and Exploitation in Northwest Alaska

Grizzly bear (Ursus arctos) densities within a 1,862 km2 study area surrounding a lead/zinc mine in northwest Alaska were estimated using mark-recapture methods during late May and early June 1987. Radio collars were used to mark bears and assess population closure. Density estimates were 1 bear/66 km2 for adults (>3-years-old) and 1 bear/5 1 km2 for bears of all ages. Some of the biases and problems associated with the mark-recapture method were discussed. Density estimates were used to estimate population size within and near the bear study area, and this estimate was compared with reported and suspected annual harvests. Estimated annual harvest rates in recent years ranged from 8 to 16%. Current bear density and population estimates will be compared with estimates obtained after the mine is developed to assess impacts on the bear population. Int. Conf. Bear Res. and Manage. 8:405-413 Conservation of brown/grizzly bears (Ursus arctos) in Alaska depends on the availability and use of assessment methods that allow game managers to monitor status of populations regularly. Historically, managers have relied on crude analyses of harvest data and miscellaneous observations to assess bear population trends and effects of harvest. However, the basis for use of harvest statistics for monitoring population status is not well documented and appears imprecise and unreliable (Harris 1984; Harris and Metzgar 1987a,b). In areas where unreported harvests are potentially large, reported harvests may not be representative of harvest mortality, and consequently, problems associated with use of harvest data for assessing population trends may be insurmountable. Fortunately, bear populations appear healthy and abundant in many areas of Alaska. If viable populations are to be maintained, appropriate methods must be developed so that managers can accurately identify and remedy population declines. Increasing human populations have significantly reduced the abundance and distribution of grizzly bears in North America (Cowan 1972). Although current abundance and distribution of bears in Alaska is similar to historical levels, alteration of important habitats could significantly alter productivity and survival of affected bear populations. Current understanding of grizzly bear population dynamics in relation to human developments is inadequate for providing effective guidelines for minimizing and mitigating impacts to bear populations. This inadequacy exists because such impacts are often long term, research is usually of short duration, and many impacts are relatively recent (Peek et al. 1987). This study was conceived in response to variations in estimates of bear abundance, and concern about potential adverse impacts from development and operation of the Red Dog Mine in northwest Alaska. This study sought to evaluate effects of human harvests by comparing bear density with known reported harvests, and to provide baseline data on bear density, structure, movements and reproductive parameters before large scale mine development. Significant changes in bear density due to the Red Dog mine will be assessed later by repeating the study using identical study methods. Background for this study was provided by Ballard (1987) and Ballard et al. (1988). This report presents and discusses use of markrecapture methods for estimating pre-mining bear densities and estimating current minimum harvest rates. The following individuals deserve recognition for their assistance during this study: L. Adams, J. Coady, A. Eliason, D. James, V. Karmun, R. Kemp, A. Lovaas, S. Machida, M. McNay, R. Nelson, S. Patten, D. Reed, J. Rood, F. Sandegren, J. Schoen, M. Shaver, R. Sheldon, and P. Walters. C. Hepler prepared figures and maps. S. Miller provided valuable advice in use of mark-recapture methods. Constructive criticism of this manuscript was providedby A. Cunning, S. Machida, S. Miller, J. Schoen, and 3 anonymous reviewers. The study was funded by the National Park Service, the Alaska Department of Fish and Game (ADF&G), and several Federal Aid in Wildlife Restoration Projects.