Brown bear population size and harvest in Northwest Alaska

Bears cross snow fields in the Brooks Range, Gates of the Arctic National Park and Preserve.

NPS/Matt Cameron

The Arctic Inventory & Monitoring Network has collected brown bear density data since 2005 across four areas: the Seward Peninsula (including much of Bering Land Bridge National Preserve), lower Noatak National Preserve, upper Noatak National Preserve, and Gates of the Arctic National Park and Preserve. The goal of our project was to estimate the size of the bear population in each area, along with estimated harvest rates, to provide a broad perspective on long-term population changes relative to harvest levels.

What we found was, in general, brown bear populations appear to be stable or slowly increasing. One exception is the lower Noatak where the bear population appears to be much larger than in the past. Estimated harvest rates were low for all three areas in the Brooks Range, providing little evidence that harvest was limiting populations in these areas. In contrast, harvest rates on the Seward Peninsula were much higher, suggesting that harvest may be approaching levels that could affect population growth. Ongoing monitoring work will help us to further understand the impacts of harvest and how bear populations may be changing through time.

Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

Abstract

Human‐caused mortality in general, and unregulated hunting in particular, have been implicated in reductions in brown bear (Ursus arctos) populations throughout much of their range. In northwestern Alaska, USA, bear densities have not been assessed in 20 years while harvest regulations have been liberalized, raising concerns that broad undetected population declines might occur. We used a modified mark‐resight approach to estimate brown bear density during 2005–2018 in 4 subareas throughout the region. We also summarized harvest information for each subarea and used our survey results to estimate harvest rates. We estimated densities for independent bears assuming constant or heterogeneous probabilities of detection and occurrence. We present the results of the constant model for more direct comparison with past work and the heterogeneity model results to provide estimates of density that are less likely to be negatively biased. Using the constant model, we estimated the density of independent bears was 17.0, 49.2, 24.9, and 19.4/1,000 km² on portions of the Seward Peninsula, the lower Noatak River, the upper Noatak River, and Gates of the Arctic National Park and Preserve, respectively. These estimates are broadly similar to those from past work in interior and northwestern Alaska, with the exception of the lower Noatak River subarea where our estimates are the highest reported for a bear population in northern Alaska. We estimated that the harvest rate on the Seward Peninsula was approximately 5.2% or 7.7% on average, depending upon the model used. In the remaining areas, we estimated annual harvest rates were <2.5%, well within sustainability guidelines from past work. Overall, our results suggest that brown bear densities are similar or somewhat higher than in the past in much of northwestern Alaska and that current harvest rates are sustainable in most areas, except perhaps the Seward Peninsula. Ongoing survey work will be useful for further evaluating the assumptions of the modified mark‐resight survey approach, assessing population trajectory, and determining the effect of harvest on brown bear populations.

Schmidt, J. H., H. L. Robison, L. S. Parrett, T. S. Gorn, and B. S. Shults. 2021. Brown bear density and estimated harvest rates in northwestern Alaska. The Journal of Wildlife Management 85(2): 202-214.