Local Species Information - Fisher (Pekania pennanti)

General Information

Fisher Natural History

Fisher from the Sierra Nevada.  Photo Credit: Rebecca Green,
Pacific Southwest Research Station

Background   

A resident of coniferous and mixed coniferous forests, the fisher once occurred throughout much of Canada, the northern United States, and the western United States. Fisher populations declined historically primarily due to loss of habitat from timber harvesting and trapping. Populations of fishers have declined in all Canadian provinces and states except the Yukon and in the extreme northeastern United States (Maine, New Hampshire, and Vermont). In the western United States and Canadian Provinces, the number of fishers has been greatly reduced and their populations fragmented.  

Identifying Characteristics

Adult fisher with radio collar.  Photo Credit: J. Mark Higley,
Hoopa Valley Tribal Forestry

Markings: The fisher is light brown to dark blackish-brown, with the face, neck, and shoulders sometimes being slightly gray. The chest and underside often has irregular white patches. The fisher has a long body with short legs and a long bushy tail. At 6.6 to 13.2 pounds, male fishers weigh about twice as much as females (3.3 to 5.5 pounds). Males range in length from 35 to 47 inches while females range from 29 to 37 inches in length. Fishers from the Pacific States may weigh less than fishers in the eastern United States.

Look-a-like Mammals  

 American Marten

American martens (Martes americana) have similar body shapes to fisher, but are smaller and usually lighter in color than fishers.  The fur on the throat of martens is a buff or orange color; legs and tails are typically darker than the rest of the body.  Female martens range from 18 to 22 inches in length and weigh 1.5 to 1.8 pounds.   Male martens range from 20 to 25 inches in length and weigh 1.6 to 2.8 pounds. 

American marten.  Photo Credit: Eugene Wier

American Mink

The American mink (Mustela vison) also has a similar body shape to fisher, but are smaller and usually darker in color than fishers.  Their fur is deep, rich brown, with or without white spots on the stomach.  American mink have webbing at the base of their toes, and their ears barely stick out above their fur.  Females range from 18 to 22 inches in length and weigh 1.2 to 1.7 pounds.  Males are slightly larger than females, ranging from 19 to 28 inches in length and 1.9 to 2.8 pounds.

American mink.  © 2004 Ron E. VanNimwegen

Geographic Range

The West Coast Distinct Population Segment includes the states of Washington, Oregon, and California. Fishers are known to occur in Oregon and California; fishers were re-introduced into the Olympic Peninsula of Washington in January and March of 2008. For more information on the re-introductions, please follow the links listed below in the Reintroductions section.

Map showing the current and historical range of fisher in the western United States.

Habitat

Fishers use forest habitats with dense canopy closure, large diameter live trees (conifers and hardwoods) and snags (dead trees) with cavities and other deformities, large diameter down wood, multiple canopy layers. Mature and Late-successional coniferous or mixed forests that contain key habitat and structural components provide the most suitable fisher habitat because they provide abundant potential den sites and preferred prey species. The physical structure of the forest (abundant structures for den and rest sites, complexity and diversity of trees and shrubs) and prey associated with these forest conditions are thought to be the critical features that explain fisher habitat use, rather than specific forest types. Fishers use habitat at multiple scales, for an example click here. The West Coast native population of fishers currently inhabits forested areas from sea level along the California/Oregon Coast to approximately 1,970 to 8,530 ft in the Trinity and Klamath/Siskiyou Mountains in northern California and southern Oregon, and Sierra Nevada in California. Fishers also currently exist in reintroduced populations in the Oregon Cascades and most recently the Olympic peninsula in Washington.

Prey

Fishers have a diverse diet that includes birds, squirrels, mice, shrews, voles, reptiles, insects, plants, fruit, and dead animals.  Small and mid-sized mammals are the most common prey items eaten by fishers in the Pacific States.  Fishers search for prey in forested stands, avoiding openings.

Reproduction

Except during the breeding season, fishers are solitary animals.  The breeding season for the fisher is generally from late February to the end of April.  Female fishers raise 1 to 3 kits, which are weaned by 10 weeks old.  When they are 1 year of age, kits have established their own home ranges and are no longer dependent upon adults.

Fisher Reproduction Cycle.  Photo Credit: Cathy Raley,

USDA Forest Service, PNW Research Station

Current Information

For additional detailed information a list of literature from the Draft Fisher Species Report pertaining to fishers, habitat, prey, and potential threats can be found by clicking here.

Interagency Fisher Species Assessments

This interagency conservation effort began in late 2005 in response to a 12-month status review and subsequent finding by the USDI Fish and Wildlife Service (2004) for the West Coast (Washington, Oregon, and California) Distinct Population Segment (DPS) of the fisher (Martes pennanti) stating that a listing was “…warranted but precluded by higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants.” Following this finding, federal and state agency leadership recognized the need for and potential benefits of developing a conservation assessment and strategy for the West Coast DPS. Agency leaders subsequently formed a steering committee to oversee the development of a Conservation Assessment (Assessment) and Conservation Strategy (Strategy) by the Interagency Fisher Biology Team. Because the range of the West Coast DPS is contiguous with historical range in British Columbia, fishers will benefit from a coordinated conservation approach that includes both countries. The geographic scope of this conservation effort thus includes south-central British Columbia. The vision for the Assessment and Strategy is to provide an effective, integrated regional approach to achieve self-sustaining, interacting populations of fishers within their historical west coast range. The three volumes of the assessment with links below are the results of the work of the interagency fisher team.
Conservation of Fishers (Martes pennanti) in South-Central British Columbia, Western Washington, Western Oregon, and California. Volume I: Conservation Assessment.

Conservation of Fishers (Martes pennanti) in South-Central British Columbia, Western Washington, Western Oregon, and California. Volume II: Key Findings from Fisher Habitat Studies in British Columbia, Montana, Idaho, Oregon and California.

Conservation of Fishers (Martes pennanti) in South-Central British Columbia, Western Washington, Western Oregon, and California. Volume III: Threat Assessment.

Toxicants in our Forests

One of the potential significant threats to fishers identified in the proposed rule is direct and indirect exposure from the illicit use of anti-coagulant rodenticides (ARs) on public and community forest lands within fisher habitat. Rodenticide exposure in fishers has been documented in the reintroduced population in Olympic National Park and in fisher populations in the Klamath Mountains and Southern Sierra Nevada. Rodenticide use has been verified at illegal marijuana cultivation sites within occupied fisher habitat on public, private and tribal lands in California.

ARs act by interfering with liver syntheses of vitamin K-dependent blood-clotting factors and damaging small blood vessels. Pregnant female fishers are considered especially at risk. AR effects can include maternal bleeding and death, spontaneous abortion, and fetal deformities. ARs can also be transferred to kits through nursing. Male fishers are also considered at risk because their much larger home range size means they can be exposed to ARs from potentially more than one illegal grow site. To date, published research indicates that of the 58 fisher carcasses studied, 79 percent tested positive for the toxins associated with ARs in California; 75 percent tested positive in Washington.

Click here for a Fisher Toxicant Fact Sheet Rodenticde (Rat Poison) exposure in West Coast Fisher populations.

Click here to view a video about fisher and rodenticides.

For additional information and resources about toxicants in our forests, please follow the links provided below:

Anticoagulant Rodenticides on our Public and Community Lands: Spatial Distribution of Exposure and Poisoning of a Rare Forest Carnivore

Integral Ecology Research Center, Toxicants in Wildlife

Poison from Marijuana Cultivation on Public Lands Threatens Fishers

Shasta Trinity National Forest: Marijuana Gardens in the Woods?

Fisher Surveys and Monitoring

Standardized Survey Protocol

American Marten, Fisher, Lynx, and Wolverine: Survey Methods for their Detection Zielinski , W.J., and Thomas E. Kucera. USDA Pacific Southwest Research Station. General Techncial Report PSW-GTR-157

Using Hair Samples and Genetic Analysis; Non-invasive Survey Techniques for Fishers

The Yreka Fish and Wildlife Office and the Klamath Basin Tribal Youth Program is engaged in the conservation of fishers and has been monitoring  fisher occupancy in the Eastern Klamath region of Northern California and Southern Oregon. Tribal intern Jesse Hogg and Service biologist John Morris produced this short video to explain the use of hairsnares and track plates to investigate fisher populations.