Occupancy modeling confirms management concerns for Connecticut (USA) fisher, highlighting the importance of monitoring furbearer distributions

Many mustelids share a history of population decline in North America following European settlement, followed by a period of restoration and recovery. Relative to their historical distributions, mustelids are now perceived to be common and widespread. However, the local conservation status of many mustelids challenges this perception. Fishers ( Pekania pennanti ) in Connecticut were considered abundant prior to the initiation of an annual trapping season in 2005, but indices of relative abundance have decreased over the last 18 years, particularly in western Connecticut. We collected detection data from camera surveys conducted in winter (December–April) in 5 km 2 units (n = 59 units, 354 cameras) throughout Connecticut between 2018 and 2023 to verify management concerns and contribute to an updated conservation assessment of fisher in the state. We applied an occupancy modeling framework to the detection data, emphasizing regional comparisons in occupancy, detection rate, and model-based density. We detected fishers across Connecticut except in the southwestern part of the state, but the area occupied was small (176 km 2 ). The model-based density estimate (λ) was much lower in Connecticut compared to an abundant fisher population in southern Vermont, and lower in western Connecticut compared to the east. Region was the best-supported covariate on occupancy in our single-season model, and parameter estimates (ψ, p) from top models were greater in eastern Connecticut compared to the west. Fishers did not show spatial segregation from other carnivores in the study but did exhibit temporal separation in daily activity patterns from other carnivores. Our results support management concerns regarding the conservation status of fisher in Connecticut, particularly in the western part of the state. The relative abundance of fisher appears low based on all metrics, and a short-term closure or reduction in the length of the trapping season in western Connecticut could benefit fisher recovery. Harvest data and other sighting metrics may be insufficient to fully assess the conservation status of mustelids such as fisher. Therefore, we recommend implementing a long-term monitoring program to provide current distribution data for fisher. Future studies should focus on understanding the impacts of anticoagulant rodenticides and canine distemper on the current decline of fisher in Connecticut.