The Pacific fisher (Martes pennanti pacifica) is a Federal Species of Concern, at risk of extinction from logging, fur trapping and habitat loss. However, politics have prevented its official listing at the federal level. The fisher is endangered in Washington, and was recently reintroduced in the Olympic National Park, WA. It is listed as a species of concern in Idaho and sensitive-critical in Oregon. Only two populations remain in California, one in the western part of the California/Oregon border and a smaller population in the southern Sierra Nevada Mountains.
The fisher is elusive, complicating efforts to track its population status. Previous attempts to determine California fisher population size and distribution relied on the functionality of track plates and photographs from scented or baited stations. While these methods are commendable for providing nonlethal detection of a species, detectability was low. Use of scented or baited stations can also lure targeted animals from their natural micro-habitat, and can potentially bias data toward areas of non-essential habitat.
The Center for Conservation Biology (CCB) employed their scat detection dogs as an alternative non-invasive method of monitoring the northern and southern fisher populations in California. The northern population study is a collaboration with the US Fish and Wildlife Service, the Hoopa Native American Reservation and Green Diamond Timber Company. The southern population study was conducted in collaboration with the US Forest Service, and Pacific Southwest Research Station.
Our initial goals were to assess the utility of scat detection dog methods for monitoring fisher populations across their range in California, hoping that results will better inform decisions regarding a federal listing. The southern California study additionally aimed to examine impacts of fuel reduction programs on the fisher.
In northern California , two detection dogs, trained to find fisher scat, were used to sample a 250 km2 area on the Hoopa Reservation and the adjacent Green Diamond Timber Company, over a six week period in July and August 2005.
Seven hundred scat samples were collected in the six week period, demonstrating a remarkably high detection rate relative to other methods. The sampling rate was very comparable between sessions for any given cell. Collection rates were approximately 1 sample/ km2 on both Green Diamond and Hoopa Land (Figure 1).
SIERRA NEVADAFishers are typically associated with dense forests with high canopy cover, multiple layers, and large trees, snags, and logs. Some of these habitat elements are also associated with high fire risk—dense trees with thick undergrowth and dead and downed woody material that act as fuel ladders by which ground fires to escalate to crown fires. These forest characteristics are also likely to be altered to some extent by forest management activities designed to reduce the high risk of fire in forests where fire has been suppressed for decades.
Although fishers are expected to ultimately benefit from the reintroduction of fire, the short-term risks associated with fuels management treatments are poorly understood. As long as the effects of fuel reduction activities remain unknown there is a potential conflict between the need to reduce fuels and short-term habitat needs of fishers.
Designing a scientifically credible study design that is not cost-prohibitive posed a challenge for fisher conservation given their low densities, secretive nature and large home ranges.
In fall 2006, we began using scat detection dogs to detect fisher habitat use at six sites in the Sierra and Sequoia National Forests, as well as monitor impacts of fuel reduction programs on the Pacific fisher. Based in part on our high sampling rate in northern California during 2005, this study used a reduced cell size, allowing us to improve efficiency by decreasing the number of surveys per cell without loss of precision. This study is still on-going.
Fisher scat detection by dogs was also high in this population despite its markedly smaller size compared to northern California. However, the lower density of fisher coupled with many other small carnivores (e.g., marten, ringtail, skunk, fox, raccoon) in the area proved somewhat more challenging for the dogs to retain their typically high species-specificity. DNA analyses for species identification is used to confirm detection of fisher versus other carnivores. We used this information to modify training methods in order to enhance the probability of detecting fisher.
Our results from these studies suggest that scat detection dog methods are ideally suited for monitoring fisher distributions over the landscape. Hopefully, these tools will fill a critical methodological void in fisher studies that can aid their conservation throughout the Pacific Northwest.
Our fisher work was supported by the US Fish and Wildlife Service and the US Forest Service Pacific SW region.