Harvest and Persistence of Wolf Populations: Variable Effects of Harvest on Wolf Packs in the Rocky Mountains
MS Thesis, Sarah Bassing (2014-2017)
Public harvest is a common method used to manage populations of wolves (Canis lupus) in North America. Although wolves appear resilient to the effects of harvest management the influences on demography and pack stability are uncertain. Packs generally drive population dynamics for wolves; thus, we were interested in how harvested populations were maintained and how harvest influenced the abundance and distribution of packs. We used noninvasive genetic data collected in Idaho, USA (2008–2014) and Alberta, Canada (2012–2014) to test whether immigration compensated for harvest mortality and helped maintain population densities. We further fit occupancy models to detection data derived from noninvasive genetic samples and hunter surveys from Alberta, Canada (2012–2014) to test the stability of pack abundance and distribution in a harvested population of wolves. We genetically identified 461 unique wolves across our study areas; 762 hunters reported seeing live wolves in southwestern Alberta. We found our hypothesis that immigration did not compensate for harvest mortality was supported. Density of wolves in the U.S. population declined from 15.49 wolves/1000 km2 (95% credible interval [CRI]: 12.38–18.57) without harvest to 10.20 wolves/1000 km2 (95% CRI: 7.47–12.90) with harvest, whereas the proportion of long-distance immigrants was low and did not change with harvest (ranged 0.01–0.02, SD = 0.1). Density and proportion of immigrants were similar among study areas where harvest occurred. We also found we could not reject our hypothesis that occurrence of packs was generally stable in a harvested population of wolves. The mean annual probability for wolf pack occupancy ranged 0.72–0.74 and the estimated distribution of wolf packs was consistent over time. Model selection indicated harvest did not have a strong effect on pack occurrence but that the probability of detecting a wolf pack was positively associated with the intensity of harvest for wolves. Although immigration did not appear to compensate for harvest mortality, pack occurrence remained generally stable over time, likely due to movement between packs from within the population. Harvest therefore appears to affect within-pack dynamics, but may not directly affect the number and distribution of packs across a population.