Population Dynamics of a Naturally Regulated Brown Bear Population on the Coast of Katmai National Park and Preserve

Sellers, Richard; Miller, Sterling; Smith, Tom; Potts, Rick

Research on brown bears (Ursus arctos) along the Katmai coast began in response to the March 24, 1989, Exxon Valdez oil spill (EVOS). Original study objectives focused on testing for population-level effects of the EVOS. Although some bears did ingest crude oil and one yearling apparently died from exposure to oil, there was no difference in survival rates or recruitment between a group of bears whose multiannual locations suggested use of oiled coastline and another group of bears that used unoiled areas (Sellers and Miller 1999). Consequently, this study evolved into Phase II of the interagency study to allow comparisons of population parameters between an unhunted population (Katmai) and a population (Black Lake) that has been subjected to different harvest levels through time (Sellers 1994). The research hypothesis addressed by the study of comparative population dynamics of three brown bear populations (Black Lake -1970s; Black Lake - current; and Katmai) is that different rates of harvest will result in different population structure, density, survival rates and recruitment. We hypothesize that higher rates of harvest will result in: (1) lower proportion of adult males, (2) higher proportion of family groups, (3) younger age structure, (4) overall lower survival rates for independent bears, but proportionally less natural mortality, (5) lower population density and (6) higher recruitment rates as a result of larger litters, higher survival rates of offspring and shorter reproductive interval. An ancillary hypothesis is that higher population density and higher proportion of adult males (which are expected to result from lower harvests) will increase competition for food and will result in: (1) smaller body size (particularly for subdominant sex/age cohorts), (2) lower reproductive rates, (3) larger home ranges, (4) higher rates of subadult dispersal and (5) more conspecific predation. Statistical testing of these hypotheses will be addressed in the final report on the Black Lake study. Here we report on the dynamics of a naturally regulated population along the coast of Katmai National Park during the period of 1989-1996. The study area is centrally located in a 14,500-km2 area of national park and state lands closed to brown bear hunting. The core study area was closed to hunting in 1931. During 1989-1996, two marked males were legally harvested outside the closed area. This is an annual harvest rate of 0.9% for males and 0.18% for the total population. This low harvest rate and the relative absence of other human-induced mortality are believed to have had minimal effects on population density and structure.