Finding fishers: determining fisher occupancy in the Northern Rocky Mountains

Abstract

Monitoring rare and elusive carnivores is inherently challenging because they often occur at low densities and require more resources to effectively assess status and trend. The fisher (Pekania pennanti) is an elusive mesocarnivore endemic to North America; in its western populations it is classified as a species of greatest conservation need. During winter of 2018-2019, we deployed remotely triggered cameras in randomly selected, spatially balanced 7.5-km × 7.5-km grid cells across a broad study area in western Montana, Idaho, and eastern Washington, USA. As part of this large-scale, multistate monitoring effort, we conducted an occupancy assessment of the Northern Rocky Mountain fisher population at a range-wide scale. We used non-spatial occupancy models to determine the current extent of fisher occurrence in the Northern Rocky Mountains and to provide baseline occupancy estimates across a broad study area and a refined sampling frame for future monitoring. We used a spatial occupancy model to determine patterns in fisher occurrence across their Northern Rocky Mountain range while explicitly correcting for spatially induced overdispersion. Additionally, we assessed factors that influenced fisher occurrence through covariate occupancy modeling that considered predicted fisher habitat, site-level environmental characteristics, and the influence of available harvest records (incidental and regulated). We detected fishers in 32 out of 318 (10%) of our surveyed cells, and estimated that overall, 160 (14%; 95% CI = 115-218) of 1,143

An overwinter protocol for detecting wolverines and other carnivores at camera traps paired with automated scent dispensers

“…Previous studies found no difference in detection probabilities for wolverines (Lukacs et al., 2020) or fishers (Krohner et al., 2022, using portions of the same data analyzed here) at CT stations paired with automated scent dispensers per our protocol versus those regularly replenished with meat baits and scent lures. These findings, in combination with cost savings and reduced risks associated with not having to visit survey stations in winter, led to the widespread application of our survey protocol for wolverine surveys conducted during winter 2021/22 in Montana, Idaho, Wyoming, Colorado, Utah, Oregon, and Washington, and for fisher surveys conducted during winter 2023/24 across Idaho and Washington (C. Mosby [Idaho Fish and Game], J. Lewis [Washington Fish and Wildlife], pers.…”

“…We deployed CTs and automated scent dispensers in the North Cascades of Washington to detect wolverines, and in the Rocky Mountains of Idaho to detect fishers, as well as nontarget species in both regions. Surveys were conducted intensively in Washington (i.e., via a high density of stations in areas known to be used by wolverines; Aubry et al., 2023), and extensively in Idaho (i.e., at lower densities within a larger study area; Krohner et al., 2022).…”

“…We implemented our overwinter dispenser protocol at 39 stations across northern Idaho during the winter of 2018/19 as part of a multi‐state effort to estimate fisher occupancy (Krohner et al., 2022). Stations were deployed in October and November in modeled fisher habitat and removed the following spring or summer after snowmelt.…”

“…We implemented our overwinter dispenser protocol at 39 stations across northern Idaho during the winter of 2018/19 as part of a multi-state effort to estimate fisher occupancy (Krohner et al, 2022).…”

“…Although adapted versions have now been used by other researchers (i.e., Krohner et al, 2022;Lukacs et al, 2020), this is the first time the protocol has been fully described in a scientific publication, and its advantages and challenges discussed. At each survey station, we selected a tree measuring >30 cm in diameter at chest height, then bolted the dispenser to the bole at a height of 3-4 m from the ground.…”