Harvest Data are Good Indices of Annual Abundance of Muskrats (Ondatra zibethicus)

Ondatra zibethicus (Muskrat) populations seem to be declining across North America, necessitating broad-scale efforts to track annual abundance dynamics. Annual harvest data for Muskrats are used to infer landscape-scale population changes, though these data are intrinsically linked to harvest effort by trappers. The number of Muskrat huts occurring in wetlands accurately reflects local population abundances, though hut abundance is difficult to survey across large landscapes. We used 17 years (2001–2018) of standardized Muskrat hut counts and harvest data from Ottawa National Wildlife Refuge, OH, to evaluate if annual harvest counts reflected the number of Muskrat huts present prior to trapping seasons. Using linear mixed-effects models, we found a positive relationship between annual hut counts prior to trapping season and annual Muskrat harvest counts. Models that included Muskrat hut counts received substantially greater support than models that did not include hut counts, indicating that annual Muskrat abundance was an important predictor of harvest. For every Muskrat hut observed prior to trapping season, 1.9 Muskrats were harvested (with extrinsic factors held at mean values). Our results provide managers with information to predict Muskrat harvest any given year where hut counts are conducted prior to trapping season. Additionally, our study is the first to link annual Muskrat harvest data to realized estimates of Muskrat abundance (inferred from hut counts), providing evidence that Muskrat harvest data may be sufficient to assess changes in Muskrat population abundances.