Western States Wolverine Conservation Project: results of the Washington Wolverine Survey, Winter 2016-2017

The wolverine (Gulo gulo) is a mid-sized carnivore and member of the weasel family (Mustelidae). This species has a circumpolar distribution (Copeland and Whitman 2003), and historically occupied most alpine and subalpine habitats in the western United States (Aubry et al. 2007), including the Cascade Range of Washington (Dalquest 1948, Ingles 1965). As with several other native carnivores, the wolverine appears to have been nearly or fully extirpated from the state, as well as most of the contiguous US, by the mid-1900s (Aubry et al. 2007, Schwartz et al. 2007). While the causes for this extirpation are unknown, direct persecution, incidental capture and mortality via predator control campaigns, unregulated trapping, and low densities combined with little or no immigration, likely contributed (see McIntyre 1995, Aubry et al. 2007).

Although wolverines were extirpated from the state, they had recolonized the Cascade Range north of Interstate 90 (I-90) in Washington by the 1990s. Reasons for the wolverine's reestablishment in Washington are poorly understood, but may relate to (1) the cessation of predator control programs by the 1970s, (2) a reduced level of persecution as a result of formal protection from commercial trapping and a 2000 Citizen's Initiative in Washington State that banned the use of body gripping traps by the general public (Initiative 713), and (3) better education about the ecological role of carnivores overall, which may have enhanced acceptance of predators. Little was known about the wolverine population in Washington prior to the initiation of the North Cascades Wolverine Study (Aubry et al. 2016), which provided the first information on the movements, use areas, habitat associations, and baseline demographic characteristics of wolverines in the Pacific Northwest. This study also demonstrated that there is a single population of wolverines that occupies the Cascade Range in Washington and southern British Columbia. Further, limited verifiable detections (e.g., photographs and genetic identifications) of wolverines over the last ~15 years indicate at least an intermittent presence of this species in the southern Cascades (i.e., south of I-90) since the mid-2000s, and a consistent presence since 2010.

Because wolverines occur at low densities and occupy remote mountainous habitats, their presence can be difficult to detect. Hence, changes in wolverine distribution are difficult to monitor without substantial efforts. The proposed listing of the wolverine in the western U.S. under the Endangered Species Act (ESA; USFWS 2010) prompted concern about the impacts of climate change on the persistence and stability of wolverine populations, which are closely associated with persistent spring snow cover (Aubry et al 2007, Copeland et al. 2010, Inman et al. 2013). The proposed listing also prompted the establishment of the Western States Wolverine Conservation Project, the aim of which is to develop measures to conserve this species. One of the Project's first actions was to conduct a regional survey of wolverines in Idaho, Montana, Washington and Wyoming.the only states where resident populations of wolverines were known to occur in the contiguous U.S.

The objectives of the western states wolverine survey were to (1) evaluate the current distribution of wolverines, (2) identify gaps in the distribution, (3) establish a baseline for assessing future changes in distribution, (4) identify factors that affect wolverine occupancy in the western U.S., and 5) generate new insights about the wolverine's status and conservation needs/opportunities at a regional scale. In this report, we describe the survey effort and summarize the results that were obtained for the state of Washington toward meeting objectives 1-3. We also report detections made of other carnivores, and discuss how our results for wolverines and other carnivores can help carnivore biologists design future survey efforts for these species in Washington.