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Pacific fisher (Martes pennanti)

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Pacific fisher (Martes pennanti)


The west coast population of the Pacific fisher is endangered due habitat loss and fragmentation, small population sizes and isolation, and human-caused mortality from incidental trapping and vehicle collisions. Logging and development have caused severe loss and fragmentation of old-growth forests and now as little as 15% of this forest type remain in California, Oregon and Washington. Forces that can reduce habitat value for fishers range from stand-replacing wildfires to management actions intended to preclude such fires by reducing the amount and continuity of forest fuels. The complex and probabilistic interplay between such habitat threats, as well as incomplete information on fisher biology, creates great uncertainty about the current health of the southern Sierra fisher population and how it is likely to change in the future.


The Pacific fisher, a relative of the mink, otter, and marten is a predator dependent upon mature and old growth forests for habitat. Fishers use large areas of primarily coniferous forests with fairly dense canopies and large trees, snags, and down logs. The fisher prefers forests with high canopy cover and mature and old-growth stands, and require large trees for denning. The fisher dens in rotting logs, hollow trees, and rocky crevices of old growth forests They are specialized animals that frequently travel along waterways and rest in or on live trees, snags, or logs with cavities. These characteristics are usually only found in large, undisturbed tracts of old forest. Douglas fir is the most common species used for resting in northern California, whereas oaks and true firs are commonly used in the southern Sierra. The diameter of trees used by fisher for resting and denning is consistently large. Rest sites are widely distributed throughout fisher habitat. Each individual travels over a home range of 50-150 square miles, even more in winter when food is scarce.


The Bush Administration’s 2004 Sierra Nevada Framework revisions have increased logging in old growth forests throughout the Sierra Nevada and particularly in key fisher habitat. The revisions to the 2001 Framework plan dismantle the Southern Fisher Conservation Area, which until the revisions were adopted, helped protect forests throughout existing fisher habitat. The revisions also increased off-highway vehicle use and road construction within the fisher’s home ranges. Severe loss and fragmentation of habitat caused by logging has lead to the near extinction of the fisher from its west coast range. The species dispersal power is low compared to the spotted owl, and they are comparatively slow to recolonize their historic range. Because the fisher cannot fly over logged areas, it can be thought of as being considerably more sensitive to fragmentation of old forests than the California spotted owl. In the Sierra Nevada, fishers currently occupy less than half their historic range, with a gap of 350 miles separating the northern and southern California populations (Zielinski et al. 2005). Having apparently been extirpated from the central and northern Sierra, a small population does persist in the southern Sierras, south from Yosemite National Park to the vicinity of the Greenhorn Mountains in southern Tulare County. The initial Giant Sequoia National Monument plan advanced by the Bush Administration sought to dramatically increase logging within the core habitat of remaining fisher populations in the southern Sierra Nevada. The Pacific fisher depends upon forest management decisions which ensure the protection of large, continuous blocks of mature and old growth forests.

Restoring and managing preferred forest habitats throughout the Sierra are essential to conserve the fisher. Maintaining connectivity of habitats is important to enable the fisher to recolonize the central and northern Sierra from the fisher populations in the south. Conservation of the fisher also necessitates protecting and restoring the black oak woodlands component of mixed-conifer forest ecosystems, conserving large deformed trees, and reestablishing patches of lush layered ground vegetation, snags, and fallen logs to provide conditions for abundant prey.


Currently, only three small, isolated populations of the Pacific fisher remain, including native populations in northwestern California and the southern Sierra Nevada and a reintroduced population in the southern Oregon Cascades. An analysis by Forest Service researchers indicates that, in the absence of stronger protection measures, the fisher is likely to become extinct in the southern Sierra within 50 years.

In 2004, the U.S. Fish and Wildlife Service found that the west coast distinct population segment of the fisher "may be at significant risk of extinction" and that protection under the Endangered Species Act is "warranted,” but that listing the species was precluded by higher priorities. For the first time in the history of the Endangered Species Act, a presidential administration, the Bush Administration, has not listed a single species as threatened or endangered without being forced to do so through petitions and/or litigation. And without a doubt, this administration also holds the worst record for the number of imperiled species it has listed while in office. A "warranted but precluded" determination (like the one the FWS made for the fisher) is only allowed if the FWS is making "expeditious progress" towards listing other species. Clearly that requirement for the warranted but precluded status is not remotely close to being fulfilled.

Scientific research:

Aubry, K.B., and J.C. Lewis. 2003. Extirpation and Reintroduction of Fishers (Martes pennanti) in Oregon: Implications for their Conservation in the Pacific States. Biological Conservation 114(1) 79-90.
Aubry, K.B. 2005. Fisher Conservation Populations in the Pacific States: Field Data Meet Genetics. U.S. Forest Service, Pacific Northwest Research Station. Science Findings, Issue 70.
Boroski, B.B., 2002. Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts. U.S. Forest Service Gen. Tech. Rep. PSW-GTR-183.
Carroll, C. 2005. A Reanalysis of Regional Fisher Suitability Including Survey Data From Commercial Forests in the Redwood Region. U.S. Forest Service, Pacific Southwest Research Station, Redwood Sciences Laboratory, Arcata, California. 18pp.
Powell, R.A., and W.J. Zielinski. 1994. The Scientific Basis for Conserving Forest Carnivores: American Marten, Fisher, Lynx, and Wolverine in the Western United States. Gen. Tech. Rep. RM-254. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. pp. 38-73.
Powell, R.A., S.W. Buskirk, and W.J. Zielinski. 2003. Fisher and Marten. In: Wild Mammals of North America: Biology, Management, and Conservation. The Johns Hopkins University Press. Pp. 635-649.
Safford, H.D. 2006. Potential Impacts of Climate Change to Fisher Habitat in California: A Preliminary Assessment. U.S. Forest Service Pacific Southwest Region. 29pp.
Truex, R.L., and W.J. Zielinski. 2005. Short-term Effects of Fire and Fire Surrogate Treatments on Fisher Habitat in the Sierra Nevada. U.S. Forest Service, Joint Fire Science Program. 26pp.
Wisely, S.M. 2004. Genetic Diversity and Structure of the Fisher (Martes Pennanti) in a Peninsular and Peripheral Metapopulation. Journal of Mammology, 85(4): 640-648.
Zielinski, W.J., T.E. Kucera, and R.H. Barrett. 1995. Current Distribution of the Fisher, Martes Pennanti, in California. California Fish and Game 81(3) 104-112.
Zielinski, W.J. 2004. Home Range Characteristics of Fishers in California. Journal Of Mammalogy, 85(4), 649-65.
Zielinski, W.J., and N.P. Duncan. 2004. Diets of Sympatric Populations of American Martens (Martes Americana) and Fishers (Martes Pennanti) in California. Journal of Mammalogy 85(3) 470–477.
Zielinski, W.J. 2004. Resting Habitat Selection by Fishers in California. Journal of Wildlife Management 68(3):475-492.
Zielinski, W.J., J. Werren, and T. Kirk. 2005. Selecting Candidate Areas for Fisher (Martes pennanti) Conservation that Minimize Potential Effects on Martens (M. americana). U.S. Forest Service, Pacific Southwest Research Station, Redwood Sciences Laboratory, Arcata, CA
Zielinski, W.J., 2005. Historical and Contemporary Distributions of Carnivores in Forests of the Sierra Nevada, California, USA. Journal of Biogeography 32, 1385–1407.
Zielinski W.J., C. Carroll, and J.R. Dunk. 2006. Using landscape suitability models to reconcile conservation planning for two key forest predators. Biological Conservation. 22pp.
Zielinski, W.J., R.L. Truex, J.R. Dunk, and T. Gaman. 2006. Using Forest Inventory Data to Assess Fisher Resting Habitat Suitability in California. Ecological Applications. 16pp.

Supporting resources:

2004 U.S. Fish and Wildlife Service Decision not to list Pacific fisher

2003 U.S. FWS Merit Ruling for Status Review of Pacific fisher

2003 Court Decision Calling on U.S. FWS to Examine Listing the Pacific fisher

2000 Petition to list as Endangered Species

California Department of Fish and Game Natural History Information

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