Comparing and Contrasting Trends in Harvest and Non-Harvest Based Indices of Furbearer Abundance

Accurately monitoring furbearer populations at broad spatio-temporal extents is an important challenge in furbearer management and managers often use metrics derived from harvest (e.g., trapper harvest surveys) and non-harvest data (e.g., roadkill and spotlight surveys) as broad-scale population indices. Variation in these metrics may be driven by diverse climatic and landscape factors yet harvest-based metrics may also be driven by socio-economic factors (e.g., pelt price), which may be independent of population size. Comparing harvest and non-harvest based metrics across furbearer species can provide insights into potential sources of variation in these metrics and the degree to which they reflect species abundance. We compared statewide trends in harvest and non-harvest based metrics for six furbearers in Illinois, raccoon (Procyon lotor), skunk (Mephitis mephitis), opossum (Didelphis virginiana), coyote (Canis latrans), red fox (Vulpes vulpes), and gray fox (Urocyon cinereoargenteus), from 1977­‑2018. Harvest metrics included harvest per trapper license, harvest per successful trapper, and total annual harvest. Non-harvest metrics included annual roadkill, spotlight, and archery deer hunter surveys. We also evaluated the effects of fur price for each species. The degree of correlation between harvest and non-harvest metrics varied across species and non-linear trends were present across metrics and species. Fur prices generally declined for canids and raccoon while remaining comparatively stable for skunk and opossum. The concordance between non-harvest metrics and per-trapper harvest suggest red and gray fox have declined in Illinois while raccoon and coyote may have increased. Harvest metrics were not consistently correlated with fur price across species. The varying degree of concordance among metrics highlights the importance of understanding how different factors (e.g., socio-economic, climatic, ecological) influence furbearer metrics to provide a better understanding of the extent to which these metrics reflect true population abundance.