| Fishers (Pekania pennanti) are medium sized mustelids endemic to North America. Two fisher populations persist in Oregon: an indigenous population in southwestern Oregon and a reintroduced population in the southern Cascades. Despite its candidacy for listing under the Endangered Species Act, current information on fisher populations in Oregon is scarce. We conducted surveys using motion-activated cameras and scat detecting dogs to assess the distribution and detectability of fishers with an occupancy modeling framework. To quantify the potential for the reintroduced population to expand, we used a spatially explicit reaction-diffusion equation. We deployed >2000 camera survey stations equating to >500 sample units operational for >35 and >60 days during winter and summer, respectively, collecting >4 million photographs (surveys 2015-2017, still in progress). Detection dog teams surveyed >90 sample units. We detected fishers at 67 unique sample units and 121 individual survey stations, confirming the presence of the indigenous and introduced populations. The southern Cascades reintroduced population appears to have shifted or contracted. Population extent was less than expected, except under our slowest growth model. We confirmed a larger indigenous population, but also with range reductions. There was no evidence of population expansion into historically occupied forests despite predicted habitat suitability.
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