|
Fisher
The
Fisher portion of this web site is currently under development
Excerpts from the 12-Month finding:
For a more complete
discussion see:
12-Month Finding
Taxonomy and Description
The fisher is classified in the order Carnivora, family Mustelidae,
subfamily Mustelinae, and is the largest member of the genus Martes
(Anderson 1994). 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 (lbs) (3 to 6 kilograms (kg)), male fishers
weigh about twice as much as females (3.3 to 5.5 lbs; 1.5 to 2.5 kg).
Males range in length from 35 to 47 inches (in) (90 to 120 centimeters
(cm)) while females range from 29 to 37 in (75 to 95 cm) in length.
Fishers are estimated to live up to 10 years (Powell 1993). |
|
| |
Fisher (Martes pennanti) Photo by: Self-portrait |
Distribution and
Status
Fishers occur in the northern coniferous and mixed forests of Canada
and the northern United States, from the mountainous areas in the
southern Yukon and Labrador Provinces in Canada southward to central
California and Wyoming, the Great Lakes and Appalachian regions, and
New England (Graham and Graham 1994; Powell 1994). The fisher’s
range was reduced dramatically in the 1800s and early 1900s through
overtrapping, predator and pest control, and alterations of forested
habitats by logging, fire, and farming (Douglas and Strickland 1987;
Powell 1993; Powell and Zielinski 1994; Lewis and Stinson 1998). Since
the 1950s, fishers have recovered in some of the central and eastern
portions of their historic range in the United States as a result
of trapping closures, changes in forested habitats (e.g., forest regrowth
in abandoned farmland), and reintroductions (Brander and Books 1973;
Powell and Zielinski 1994). In recent decades, the scarcity of detections
in Washington, Oregon, and the northern Sierra Nevada indicates that
the fisher may be extirpated or reduced to very low numbers in much
of this area (Aubry and Houston 1992; Zielinski et al. 1995; Aubry
and Lewis 2003). |
Population Size
Although reductions in the fisher’s distribution in the Pacific
States are well documented (Aubry and Lewis 2003; Gibilisco 1994; Powell
and Zielinski 1994), accurate information on fisher densities and abundance
outside the northeastern United States is very limited. Estimates of fisher
abundance and vital rates (e.g., survival, reproduction) are very difficult
to obtain (Douglas and Strickland 1987) and may vary widely based on habitat
composition and prey availability (York 1996). Despite the lack of precise
empirical data on fisher numbers in the western states, it is likely extant
fisher populations are small due to the relative reduction in the range
of the fisher on the West Coast and the lack of detections or sightings
over much of its historical distribution. |
| |
Diet and Foraging Habitats
The fisher is an opportunistic predator with a diverse diet that includes
birds, squirrels, mice, shrews, voles, reptiles, insects, carrion, vegetation,
and fruit (Powell 1993; Martin 1994; Zielinski et al. 1999; Zielinski
and Duncan, in press 2003). Fishers hunt exclusively in forested habitats
and generally avoid openings (Earle 1978; Rosenberg and Raphael 1986;
Powell 1993; Buskirk and Powell 1994; Jones and Garton 1994; Seglund 1995;
Dark 1997). Being dietary generalists, fishers tend to forage in areas
where prey is both abundant and vulnerable to capture (Powell 1993). Selection
of foraging habitat may be driven by habitat relationships of primary
prey species. |
| |
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
(Leonard 1986; Douglas and Strickland 1987; Powell 1993; Frost and Krohn
1997). Raised entirely by the female, kits are completely dependent at
birth and weaned by 10 weeks (Powell 1993). The mother becomes increasingly
active as kits grow in order to provide enough food (Arthur and Krohn
1991; Powell 1993), and females may move their kits periodically to new
dens (Arthur and Krohn 1991). At 1 year, kits will have developed their
own home ranges (Powell 1993). Fishers have a low annual reproductive
capacity, and reproductive rates may fluctuate widely from year to year
(Truex et al. 1998). |
| |
Home Range Size
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
(Buck et al. 1983; Truex et al. 1998). Fisher home range sizes across
North America vary from 3,954 to 30,147 acres (ac) (16 to 122 km2 for
males and from 988 to 13,096 ac (4 to 53 km2 for females (Powell and Zielinski
1994; Lewis and Stinson 1998). |
| |
Habitat
According to Buskirk and Powell (1994), the physical structure of the
forest and prey associated with forest structures are thought to be the
critical features that explain fisher habitat use, rather than specific
forest types. Powell (1993) stated that forest type is probably not as
important to fishers as the vegetative and structural aspects that lead
to abundant prey populations and reduced fisher vulnerability to predation,
and that they may select forests that have low and closed canopies. In
the Klamath and north coast regions of California, Carroll et al. (1999)
also found a strong association with high levels of tree canopy cover,
tree size class, and percent conifer. Within a given region, the distribution
of fishers is likely limited by elevation and snow depth (Krohn et al.
1997), and fisher are unlikely to occupy forest habitats in areas where
elevation and snow depth act to limit their movements. |
| |
Resting and Denning Habitat
Powell and Zielinski (1994) and Zielinski et al. (2004) suggest that habitat
suitable for resting and denning sites may be more limiting for fishers
than foraging habitat. Numerous studies have documented that fishers in
the western United States utilize stands with certain forest characteristics
for resting and denning such as large trees and snags, coarse woody-debris,
dense canopy closure and multiple-canopy layers, large diameter hardwoods,
and steep slopes near water (Powell and Zielinski 1994; Seglund 1995;
Dark 1997; Truex et al. 1998; Self and Kerns 2001; Aubry et al. 2002;
Carroll et al. 1999; Mazzoni 2002; Zielinski et al. 2004). Rest sites
have structures that provide protection from unfavorable weather and predators.
Re-use of rest sites is 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 (Powell and Zielinski
1994; Truex et al. 1998), and spatially interconnected with foraging habitats. |
| |
Rest Site—Stand Characteristics
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
(Zielinski et al. 2004). 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). |
| |
Rest Site Structure Type and Size
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 (Heinemeyer and Jones 1994; Higley et al. 1998;
Mazzoni 2002; Zielinski et al. 2004). 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 (Zielinski et al. 2004). |
| |
Significance of West Coast Populations
to the Species
The forests inhabited by fishers on the west coast lack the extensive
broadleaf hardwood component that is common in the eastern portions of
the species’ range. Fishers on the west coast primarily occur in
habitat in steep, mountainous terrain, while those in the Great Lakes
region, eastern Canada, and the northeastern United States inhabit level
terrain or low lying glaciated mountains. The loss of the West Coast populations
of the fisher would eliminate the entire southwest portion of the fisher’s
North American range. Additionally, the West Coast populations of the
fisher represents the southernmost range of the Martes genus. The West
Coast populations represent three of the known remaining four populations
in the western United States (fourth being the Rocky Mountain population),
and a significant portion of the western range of fishers in North America.
The loss of the species from the United States west of the Rocky Mountains
and south of British Columbia would result in a significant gap in the
range of the species as a whole and represent the loss of a major geographical
area of the range of the taxon. It would represent a loss of the species
from about 20 percent of its historical range in the United States, a
significant portion of its North American range. |
| |
Factors Affecting the Species
Timber
Harvest - The extent of past timber harvest
is one of the primary causes of fisher decline across the United States
(Powell 1993), and may be one of the main reasons fishers have not recovered
in Washington, Oregon, and portions of California as compared to the northeastern
United States (Aubry and Houston 1992; Powell and Zielinski 1994; Lewis
and Stinson 1998; Truex et al. 1998). Timber harvest can fragment fisher
habitat, reduce it in size, or change the forest structure to be unsuitable
for fishers. Habitat fragmentation has contributed to the decline of fisher
populations because they have limited dispersal distances and are reluctant
to cross open areas to recolonize historical habitat.
Fuels Reduction
and Loss of Habitat From Fire - Mechanical thinning or prescribed
fire negatively affect fishers if it impacts habitat quality by reducing
canopy cover and coarse woody debris over large areas or fragment habitat.
Prescribed burning generally promotes forest health, and can enhance suitability
for wildlife, but may vary in its effect on fishers. Small fires should
not be detrimental to fishers because of the fishers’ large home ranges
(unless they impact natal dens during breeding season); however, hotter
or more widespread fires may displace fishers or destroy habitat. Prescribed
fire can also consume habitat structural elements such as snags and downed
logs that are important to fishers or their prey.
Forest Disease
and Insect Outbreaks - Although large area epidemics may displace
fishers if canopy cover is lost, the usual pattern of localized outbreaks
and low density of insect and disease damage is probably not a great threat
to fisher habitat. In some cases, the diseased trees are beneficial, providing
structures conducive to resting and denning.
Development,
Recreation, and Roads - Forested area in the Pacific coast
region decreased by about 8.5 million ac (34,400 km2) between 1953 and 1997
(Smith et al. 2001). Alig et al. (2003) state that ‘‘Forest
cover area [in the Pacific coast states] is projected to continue to decrease
through 2050, with timberland area projected to be about 6 percent smaller
in 2050 than in 1997. Population and income are expected to further fuel
development in the region, as population is projected to increase at rates
above the national average, leading to more conversion of forest to nonforest
uses.’’ Rural and recreational development, such as campgrounds,
recreation areas, and hiking, biking, off-road vehicle and snowmobile trails,
may adversely affect fishers. Roads Highways and associated developments
can substantially influence movement patterns of wildlife (Bier 1995). The
adverse effects of roads include direct loss of habitat, displacement from
noise and human activity, and direct mortality. The impacts of these effects
on low density carnivores like fishers are more severe than most other wildlife
species due to their large home ranges, relatively low fecundity, and low
natural population density.
Overutilization
for commercial, recreational, scientific, or educational purposes. – The fisher was commercially trapped from the early-1800s but trapping
has been prohibited in Washington (Lewis and Stinson 1998) since 1933, Oregon
since 1937 and in California since 1946 (Aubry and Lewis 2003). Where trapping
is legal in other states and in Canada, it is a significant source of mortality.
Aubry and Lewis (2003) state that overtrapping appears to have been the
primary initial cause of fisher population losses in southwestern Oregon.
Although it is currently not legal to trap fishers intentionally in California,
Oregon and Washington, they are often incidentally captured in traps set
for other species (Earle 1978; Luque 1983; Lewis and Zielinski 1996).
Disease
or Predation. - Fishers are susceptible to many viralborne
diseases, including rabies (Family Rhabdoviridae), canine and feline distemper
(Mobillivirus sp.), and plague (Yersinia pestis). Contact between fishers
and domesticated dogs and cats and other wild animals susceptible to such
diseases may lead to infection in fishers.
Inadequacy
of Existing Regulatory Mechanisms. - Existing regulatory mechanisms
that could provide some protection for the fisher include: (1) Federal laws
and regulations; (2) State laws and regulations; and (3) local land use
processes and ordinances. However, these regulatory mechanisms have not
prevented continued habitat fragmentation and modification or incidental
trapping. Although many States, Tribes, and Federal agencies recognize the
fisher as a species which has declined substantially, their use of available
regulatory mechanisms to conserve the species is limited. There are no regulatory
mechanisms that specifically address the management or conservation of functional
fisher habitat. However, the states in the petitioned area provide the fisher
with protections from hunting and trapping, and regulatory mechanisms governing
timber harvests incidentally provide conservation benefits for the fisher.
Other natural
or manmade factors affecting the continued existence of the species. - Fisher populations in the West Coast populations are small and isolated
and may be threatened by numerous factors including inbreeding depression
and unpredictable variation (stochasticity) in demographic or environmental
characteristics. Other natural or anthropogenically-influenced factors,
including urban development, barriers to dispersal, contaminants, pest control
programs, non-target poisoning, stand-replacing fire, timber harvest, accidental
trapping in manmade structures, decrease in prey base, and climate change
may cause additional fisher declines. Because of small population size,
accidental death is a threat. |
| |
Steering Committee Presentation
|
|
