Estimating Harvest Rates of Bears from Sex Ratio Changes

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Abstract
Using simulation modeling, we assessed the potential for estimating harvest rates for generalized bear (Ursus spp.) populations from changes in kill sample sex ratios (Paloheimo and Fraser 1981, Fraser 1984). Models underlying these techniques require assumptions that may be violated in the field. We found that both estimators were sensitive to violations of 4 critical assumptions, and that bias was generally most pronounced when applied to bear populations with low harvest rates, moderate differences in hunting vulnerability between sexes, and complex age structures. Additionally bears typically occur in low densities and yield small harvests, producing limited data from which harvest estimates are produced. Chance deviations from the expected patterns occurred with small (20-180) samples of harvested bears, producing substantial variability in year-to-year estimates.