Pacific fisher (Martes pennanti)

News alert: Fisher translocation proposal

The California Department of Fish and Game has released a Notice of Intent (Jan. 9) to approve a controversial plan to permit the capture and release of 40 Pacific fisher on lands owned by Sierra Pacific Industries (SPI) in the Northern Sierra Nevada. The plan, proposed by SPI, will give the company a free pass to continue their industrial timber harvest model without consequences or restrictions, even if the Pacific fisher is listed under the Endangered Species Act in the future.

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Life History

The rarely encountered Pacific fisher is in the family Mustelidae, the largest member of the genus Martes. The only other North American member of the genus Martes is the American marten (M. americana). 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 lbs). Males range in length from 35 to 47 inches while females range from 29 to 37 in long. Fishers are estimated to live up to 10 years.

The diet of the fisher includes birds, snowshoe hares, squirrels, mice, shrews, voles, porcupines, reptiles, insects, carrion, vegetation, and fruit. Fishers hunt exclusively in forested habitats and generally avoid openings. Being dietary generalists, fishers tend to forage in areas where prey is both abundant and vulnerable to capture. Selection of foraging habitat may be driven by habitat relationships of primary prey species.

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. Raised entirely by the female, kits are completely dependent at birth and weaned by 10 weeks. The mother becomes increasingly active as kits grow in order to provide enough food, and females may move their kits periodically to new dens. At 1 year, kits will have developed their own home ranges. Fishers have a low annual reproductive capacity, and reproductive rates may fluctuate widely from year to year.

Habitat

The 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 mature and old-growth forests with high canopy cover, and requires 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 oak, white fir, and red fir 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. A home range is an area repeatedly traveled by an individual in its normal activities (i.e. feeding, drinking, and resting). Fishers have large home ranges and male home ranges are considerably larger than those of females. Fisher home range sizes across North America vary from 3,954 to 30,147 acres (16 to 122 square kilometers for males and from 988 to 13,096 ac (4 to 53 square km for females).

Rest sites are natural structures that provide protection from unfavorable weather and predators. Re-use of rest sites are relatively low (14 percent: Zielinski et al. 2004), indicating that habitats providing suitable resting structures need to be widely distributed throughout home ranges of fishers and spatially interconnected with foraging habitats.

Rest site structures used by fishers include: cavities in live trees, snags, hollow logs, fallen trees, canopies of live trees, platforms formed by mistletoe (‘‘witches brooms’’) or large or deformed branches, and to a lesser extent stick nests, rocks, ground cavities, and slash and brush piles. Tree size, age, and structural features are important characteristics of a rest structure. Zielinski et al. (2004) stated that rest structures in their study areas in the North Coast and the southern Sierra Nevada were among the largest diameter trees available. Trees must be large and old enough to bear the type of stresses that initiate cavities, and the type of ecological processes (e.g., decay, woodpecker activity) that form cavities of sufficient size to be useful to fishers; tree species that typically decay to form cavities in the bole are more important than those that do not.

The most influential variables affecting rest site selection in California fisher populations include maximum tree sizes and dense canopy closure, but other features are important to rest site choice as well, such as large diameter hardwoods, large conifer snags, and steep slopes near water. Fishers select areas as rest sites where structural features are most variable but where canopy cover is least variable, suggesting that resting fishers place a premium on continuous overhead cover but prefer resting locations that also have a diversity of sizes and types of structural elements (Zielinski et al. 2004).

Threats

The west coast population of the Pacific fisher is endangered due to habitat loss and fragmentation, small population sizes and isolation, and human-caused mortality from incidental trapping and vehicle collisions. Timber harvest can fragment fisher habitat, reduce it in size, or change the forest structure to be unsuitable for fishers. Fisher are also reluctant to cross open areas to recolonize historical habitat. Logging and development have caused severe loss and fragmentation of old-growth forests--as little as 5 percent of this forest type remains in the Sierra Nevada. Stand replacing wildfires, as well as management activities designed to prevent such fires by reducing the amount and continuity of forest fuels, all can result in significant reduction in suitable habitat needed to provide for fisher viability. 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. Global climate change is also predicted to have severe impacts in the Sierra Nevada, with greatly reduced snow pack in the winter and increased drought and wildfires in the region, thereby underscoring the need to protect the remaining habitat for this species and others that also require old forest attributes.

Conservation

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 has less dispersal power compared to another imperiled species, the California spotted owl, and they are comparatively slow to recolonize their historic range. Because the fisher cannot fly over logged areas, it is considerably more sensitive to fragmentation of old forests than the 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 is 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.

Status

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.