Federal Register: April 8, 2004 (Volume 69, Number 68)
DOCID: FR Doc 04-7941
DEPARTMENT OF THE INTERIOR
Veterans Affairs Department
CFR Citation: 50 CFR Part 17
NOTICE: Part V
DOCUMENT ACTION: Notice of 12-month petition finding.
SUBJECT CATEGORY:
Endangered and Threatened Wildlife and Plants; 12-month Finding for a Petition to List the West Coast Distinct Population Segment of the Fisher (Martes pennanti )
DATES: The finding announced in this document was made on April 2, 2004. Comments and information may be submitted until further notice.
DOCUMENT SUMMARY:
We, the U.S. Fish and Wildlife Service (Service), announce a 12month finding for a petition to list the West Coast distinct population segment of the fisher (Martes pennanti) under the Endangered Species Act of 1973, as amended. After review of all available scientific and commercial information, we find that the petitioned action is warranted, but precluded by higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants. Upon publication of this 12month petition finding, this species will be added to our candidate species list. We will develop a proposed rule to list this population pursuant to our Listing Priority System.
SUMMARY:
Interior Department, Fish and Wildlife Service,
SUPPLEMENTAL INFORMATION
Background
Section 4(b)(3)(B) of the Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et seq.), requires that, for any petition to revise the List of Threatened and Endangered Species that contains substantial scientific and commercial information that listing may be warranted, we make a finding within 12 months of the date of the receipt of the petition on whether the petitioned action is: (a) Not warranted, or (b) warranted, or (c) warranted but that the immediate proposal of a regulation implementing the petitioned action is precluded by other pending proposals to determine whether any species is threatened or endangered, and expeditious progress is being made to add or remove qualified species from the List of Threatened and Endangered Species. Section 4(b)(3)(C) of the Act requires that a petition for which the requested action is found to be warranted but precluded shall be treated as though resubmitted on the date of such finding, i.e., requiring a subsequent finding to be made within 12 months. Such 12month findings are to be published promptly in the Federal Register.
On December 5, 2000, we received a petition dated November 28, 2000, to list a distinct population segment (DPS) of the fisher, including portions of California, Oregon, and Washington, as endangered pursuant to the Act, and to concurrently designate critical habitat for this distinct population segment. A court order was issued on April 4, 2003, by the U.S. District Court, Northern District of California, that required us to submit for publication in the Federal Register a 90day finding on the November 2000 petition (Center for Biological Diversity, et al. v. Norton, et al., No. C 012950 SC). On July 10, 2003, we published a 90day petition finding (68 FR 41169) that the petition provided substantial information that listing may be warranted and initiated a 12month status review. Through a stipulated order, the court set a deadline of April 3, 2004, for the Service to make a 12 month finding under 16 U.S.C. 1533 (b)(3)(B).
Taxonomy
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 (Martes pennanti Erxleben 1777) is the only extant species in its subgenus Pekania.
Goldman (1935) recognized three subspecies of fisher, although he stated they were difficult to distinguish. Both Grinnell et al. (1937) and Hagmeier (1959) examined specimens from across the range of the fisher and concluded that differences in skull morphology or pelage were not sufficient to support recognition of separate subspecies. Hall (1981) retained all three subspecies in his compilation of North American mammals, as did Anderson (1994), but neither addressed Hagmeier's conclusion that the subspecies should not be recognized (Powell 1993). Several authors address genetic variation in fisher populations in their northern and eastern ranges (Williams et al. 1999, 2000; Kyle et al. 2001) and in the west (Drew et al. 2003; Aubry and Lewis 2003; Wisely et al. in litt. 2003). These analyses found patterns of population subdivision similar to the earlier described subspecies (Drew et al. 2003). Drew et al. (2003) stated that, although it is not clear whether Goldman's (1935) subspecific designations are taxonomically valid, ''* * * it is clear (based on genetic results) that population subdivision is occurring within the species, especially among populations in the western USA and Canada.''
Description
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. The fishers from the Pacific States may weigh less than fishers in the eastern United States (Seglund 1995; Dark 1997; Golightly 1997; Aubry and Lewis 2003). Fishers are estimated to live up to 10 years (Powell 1993).
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 [[Page 18771]]
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). However, fishers are still absent
from their former range southeast of the Great Lakes (Gibilisco 1994).
Grinnell et al. (1937) estimated extremely low population numbers for
the fisher in California at a time when trapping for the fur trade had
greatly reduced populations of furbearing animals. Although it is
possible that fisher populations recovered somewhat immediately
following the trapping prohibitions in the 1930s and 40s, Powell and
Zielinski (1994) more recently note population declines for fisher
populations in the west. Fishers are believed to be extirpated from the
lower mainland of British Columbia; however, they may still occupy the
higher elevations of these areas in low densities (BC Species and
Ecosystems Explorer 2003). In the Pacific States, fishers were
historically more likely to be found in low to midelevation forests up
to 8,200 feet (ft) (2,500 meters (m)) (Grinnell et al. 1937; Schempf
and White 1977; Aubry and Houston 1992). 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).
Washington
The fisher historically occurred both east and west of the Cascade Crest in Washington (Scheffer 1938; Aubry and Houston 1992). Lewis and Stinson (1998) conclude that, ``Based on habitat, the historical range of fishers in Washington probably included all the wet and mesic forest habitats at low to midelevations. The distribution of trapping reports and fisher specimens collected in Washington confirms that fishers occurred throughout the Cascades, Olympic Peninsula, and probably southwestern and northeastern Washington.'' Aubry and Houston (1992) compared current and historical records of fishers in Washington to determine their distribution in relation to major vegetation and elevation zones. In total, they found 88 reliable records, dating from 1955 to 1991. West of the Cascades, fishers occurred from 328 to 5,900 ft (100 to 1800 m), with most records from below 3,280 ft (1,000 m). On the east slope of the Cascades where precipitation is lower, fishers were recorded from 1,970 to 7,200 ft (600 to 2,200 m) (Aubry and Houston 1992). Similar to elsewhere in the range, the upper elevational limit may be determined by snow depth (Krohn et al. 1997). Based on a lack of recent sightings or trapping reports, the fisher is considered to be extirpated or reduced to scattered individuals in Washington (Aubry and Houston 1992; Lewis and Stinson 1998).
Oregon
Aubry and Houston (1992) noted that most fisher records for Washington occurred in the western hemlock and sitka spruce forest zones. Given that these forest zones occupy large portions of northwestern Oregon (Franklin and Dyrness 1988), it is likely that the fisher historically occurred in this part of the State. Based on extensive camera and track plate surveys, Lewis and Stinson (1998) concluded that the fisher is greatly reduced in Oregon. Based on extensive inquiry and review of records, Aubry and Lewis (2003) found that extant fisher populations in Oregon are restricted to two disjunct and genetically isolated populations in the southwestern portion of the State: one in the northern Siskiyou Mountains of southwestern Oregon and one in the southern Cascade Range. The fishers in the Siskiyou Mountains near the California border are probably an extension of the northern California population (Aubry and Lewis 2003). The population in the southern Cascade Range is reintroduced and is descended from fishers that were translocated to Oregon from British Columbia and Minnesota (Aubry and Lewis 2003). The Oregon Cascade Range population is separated from known populations in British Columbia by more than 404 miles (mi) (650 kilometers (km)) (Aubry and Lewis 2003). California
In eastern California, the fisher historically ranged throughout the Sierra Nevada, from Greenhorn Mountain in northern Kern County northward to the southern Cascades at Mount Shasta (Grinnell et al. 1937). In western California, it ranged from the Klamath Mountains and north Coast Range near the Oregon border southward to Lake and Marin Counties (Grinnell et al. 1937). Krohn et al. (1997) note that the map of fisher distributions by Grinnell et al. (1937) suggests that fishers may have been less common in the central Sierra Nevada than elsewhere in California during the early 1900s, but it is unknown whether this distribution was the historical condition or reflects human effects on forests and fishers prior to their assessment. The map was based on the trapping records of one 5year period prior to which there was already concern that trapping had dangerously decreased the population of fisher in California (Grinnell et al. 1937).
Substantial efforts have been made in recent years to assess the status of fishers and other forest carnivores in California using systematic grids of baited track and camera stations (Zielinski et al. 1995, 1997a, 1997b, 2000; Zielinski and Stauffer 1996; Zielinski 1997). Recent surveys indicate that fishers appear to occupy less than half of the range they did in the early 1900s in California, and this population has divided into two remnant populations that are separated by approximately 260 mi (420 km) (Zielinski et al. 1995), almost four times the species' maximum dispersal distance as reported by York (1996) for fishers in Massachusetts. One population is located in northwestern California and the other is in the southern Sierra Nevada Mountains. Since 1990, there have generally been no detections outside these areas except for one in 1995 in Mendocino County and one in 1995 in Plumas County (CDFG 2002, updated November 13, 2003).
Failure to detect fishers in the central and northern Sierra Nevada, despite reports of their presence there by Grinnell et al. (1937) and reports from the 1960s collected by Schempf and White (1977), suggests that the fisher population in this region has declined, effectively isolating fishers in the southern Sierra Nevada from fishers in northern California (Truex et al. 1998; Lamberson et al. 2000). However, prior to the recent development of a rigorous fisher survey protocol, differences in the type and quality of data available over the previous 60year period make interpretation of distributional changes difficult (Zielinski et al. 1995).
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.
There have been no good population estimates for fisher populations in
California, Oregon, and Washington, so it is unknown precisely how many
fishers exist. 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). In addition, the assumptions of [[Page 18772]]
many methods for estimating populations (e.g., equal trapability, no
learned trap response, sufficient trapability to yield adequate sample
sizes) may not be valid for fishers (Powell and Zielinski 1994).
Consequently, only a few estimates of local fisher population density
are available for the Pacific States and British Columbia, and are summarized here.
In British Columbia, densities of fishers are estimated to be between 1 and 1.54 fishers per 38.6 mi \2\ (100 km \2\) in the highest quality habitats in the province (Weir 2003). Using the area of each habitat capability rank within the extent of occurrence of fishers in British Columbia, the latewinter population for the province is estimated to be between 1,113 and 2,759 fishers (Weir 2003). In a preliminary progress report of fisher studies on the Hoopa Valley Indian Reservation in the Klamath mountain range (Humboldt County, California), Higley et al. (1998) report high capture numbers and small home ranges, some of which overlap each other, indicating that densities in this 25 mi \2\ (65 km \2\) study area may be very high relative to those in the rest of the occupied West Coast range. In their analysis of two fisher studies in California, Zielinski et al. (in press 2003a) provided a rough estimate of approximately 5 female fishers per 38.6 mi \2\ (100 km \2\) for their 154 mi \2\ (400 km) north coast study area (in the Six Rivers and ShastaTrinity National Forests of southeastern Humboldt and southwestern Trinity Counties), whereas they estimated approximately 8 females per 100 km \2\ in their 108 mi \2\ (280 km \2\) southern Sierra Nevada study area (in the Sequoia National Forest in Tulare County). For the purpose of modeling population viability, Lamberson et al. (2000) estimated that there were between 100 and 500 individuals in the southern Sierra Nevada fisher population. Based on trapping records from the 1920s, Grinnell and colleagues (1937) provided a dire estimate of 1 fisher per 100 mi \2\, or 300 in California. However, although Grinnell et al. employed accepted methodologies at the time they conducted their research, we believe that their population estimate for California is incorrect by modern standards due to the lack of a significant sample size, survey bias, and inadequate knowledge of the historical baseline.
Despite the lack of precise empirical data on fisher numbers in the western states, the relative reduction in the range of the fisher on the West Coast, the lack of detections or sightings over much of its historical distribution, and the high degree of genetic relatedness within some populations (esp., native fishers in California) (Drew et al. 2003), indicate that it is likely extant fisher populations are small.
Diet
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).
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). Birth occurs nearly 1 year after copulation, due to delayed implantation in which the embryos remain in a state of arrested development for approximately 10 months. Arthur and Krohn (1991) and Powell (1993) speculate that this system allows adults to breed in a time when it is energetically efficient, while still giving kits adequate time to develop before winter. 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 of feeding, drinking, resting, and traveling. 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 km \2\ for males and from 988 to 13,096 ac (4 to 53 km \2\ for females (Powell and Zielinski 1994; Lewis and Stinson 1998). However, Beyer and Golightly (1996) reported that male home ranges in northern California may be as large as 31,629 ac (128 km\2\).
Truex et al. (1998) compared fisher home range sizes in three study areas: the Klamath Mountains (ShastaTrinity National Forest, the North Coast Ranges), Six Rivers National Forest, and the southern Sierra Nevada (Sequoia National Forest). They found the largest home range sizes in the eastern Klamath study area in northern California where habitat quality was generally considered poor. A preliminary summary of an unpublished study conducted in coastal redwood forests in the Coast Ranges of northwestern California indicates female home range sizes of 790 to 2050 ac (3.2 km \2\ to 8.3 km \2\) (Joel Thompson unpublished data; Neal Ewald, pers. comm. 2003), which is somewhat larger than range sizes reported by other researchers for the species in North America. Zielinski et al. (in press 2003a) found that females had home ranges that were almost three times larger in their northern California study area in the Coast Ranges than in their southern Sierra Nevada study area. They too suggest that this difference in home range size is a result of better quality habitats in the southern Sierra Nevada, which are occupied by a higher density of animals within a smaller area of suitable habitat (Zielinski et al., in press 2003a). Based on northeastern fisher home range sizes, Allen (1983) assumed that a minimum of 62 mi \2\ (161 km \2\ of potentially suitable and connected habitat must be present before an area can sustain a population of fishers. However, Allen's estimates of amount of habitat required to support a fisher population may be an underestimate when applied to western forests, where male home ranges have been found to be somewhat larger (Beyer and Golightly 1996).
Dispersal
Dispersal (movement away from the natal home range) is the primary
mechanism for the spread of a population. Arthur et al. (1993) reported
an average maximum dispersal distance of 9.3 and 10.7 mi (14.9 and 17.3
km) for females and males, respectively (range = 4.7 to 14.0 mi (7.5 to
22.6 km) for females and 6.8 to 14.3 mi (10.9 to 23.0 km) for males) in
a population in Maine with high trapping mortality and low density. In
areas with high mortality and low density, young fishers may not have
to disperse as far in order to find unoccupied home ranges (Arthur et
al. 1993). York (1996) reported dispersal distances for juvenile male and female fishers averaging 20 mi (33
[[Page 18773]]
km) (range = 6 to 66 mi; 10 to 107 km) for a highdensity population in
Massachusetts. Based on field observation and microsatellite genotype
analyses of the southern Cascades fisher population, Aubry et al. (USDA
Forest Service, Pacific Northwest Research Station, in press 2003)
found empirical evidence of malebiased juvenile dispersal and female
philopatry (the drive or tendency of an individual to return to, or
stay in, its home area) in fishers, which may have a direct bearing on
the rate at which the fisher may be able to colonize formerly occupied areas within its historical range.
Habitat
Assessment of habitat relationships of fisher in current western U.S. forests is complicated by broadscale changes in forest structure and composition over the past century. Grazing, wildfire suppression, and timber harvest have resulted in dramatic changes in forest ecosystems, including reduction of large tree component, increased dominance of shadetolerant conifer species, increased stand density, and reduced structural diversity (McKelvey and Johnson 1992; Agee 1993; Skinner 1995; Chang 1996; Norman 2003). These effects vary among forest ecosystems, but generally are more pronounced in drier interior forests of the eastern Cascades, Sierra Nevada, and eastern Klamath Mountain ranges. The degree to which currentlydescribed habitat relationships, particularly at broader scales, existed under historical conditions is unknown.
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. However, in midelevation areas with intermediate snow depth, fishers may use dense forest patches with large trees because the overstory closure increases snow interception (Weir 1995a).
In a trackplate study conducted on private timberlands in the redwoodDouglasfir transition zone of the Coast Ranges of northwestern California, Klug (1997) detected fishers on 238 occasions at 26 of 40 (65 percent) survey segments located in secondgrowth Douglasfir and redwood. Fishers were detected more frequently than expected (based on availability) in areas at higher elevations, in stands where Douglas fir was the dominant or codominant vegetation type, and with greater amounts of hardwoods. Klug (1997) found no relation between fisher occurrence and stand age or oldgrowth habitats; however there was less than 2 percent oldgrowth on his study area. The mean canopy cover for all stations Klug sampled was 94.7 percent, and mean stand age was 42.6 years, an age which, in productive lowland redwood and Douglasfir habitats, often correlates with largetree conditions. During subsequent studies in this area (Ewald, pers. comm. 2003), 24 individual fisher were captured (10 males, 14 females). Nine of 11 adult females showed signs of reproduction, and 9 natal and maternal dens were located. In their adjacent study area in Redwood National and State Parks with coastal forests dominated by redwood, Slauson et al. (2003) found that redwood was the dominant overstory and understory species where fishers were detected; Douglasfir was dominant at sites where they were not. This study area had 38 percent oldgrowth habitat; however, fisher were detected more often in secondgrowth redwood stands. In contrast to forests further north and further inland, the milder temperature and higher humidity in these coastal areas may create suitable habitat conditions, at least for foraging, in younger forests.
Fragmentation
A number of studies have shown that the fisher avoids areas with little forest cover or significant human disturbance and conversely prefers large areas of contiguous interior forest (Coulter 1966; Kelly 1977; Buck 1982; Mullis 1985; Rosenberg and Raphael 1986; Arthur et al. 1989a; Powell 1993; Jones and Garton 1994; Seglund 1995; Dark 1997).
Rosenberg and Raphael (1986) assessed forest fragmentation in northwestern California and its effect on fishers. Their study shows a significant positive association with a plot's distance to a clearcut, and significant negative associations with a stand's length of edge, degree of insulation (defined as ``the percentage of its perimeter that was clearcut edge''), percent clearcut, and total edge. Rosenberg and Raphael (1986) state, ``Among the species suspected of being most sensitive to forest fragmentation in our study, only the fisher and spotted owl were also associated with oldgrowth forests.'' They show a significant positive association between fisher presence and forest stand area, detecting fishers more frequently in stands over 247 ac (100 ha) (70 percent frequency of occurrence) and stands of 126 to 247 ac (51 to 100 ha) (90 percent frequency of occurrence) than in smaller stands; fishers were detected in 55 percent of stands that were 52 to 124 ac (21 to 50 ha), in 30 percent of stands that were 27 to 49 ac (11 to 20 ha), and in 17 percent of stands under 25 ac (10 ha).
The fisher's need for overhead cover is very welldocumented. Many researchers report that fishers select stands with continuous canopy cover to provide security cover from predators (de Vos 1952; Coulter 1966; Kelly 1977; Arthur et al. 1989; Weir and Harestad 1997, 2003). Fishers may use forest patches with large trees because the overstory closure increases snow interception (Weir 1995a). Forested areas with higher density overhead cover provide the fisher increased protection from predation and lower the energetic costs of traveling between foraging sites. Fishers probably avoid open areas because in winter open areas have deeper, less supportive snow which inhibits travel (Leonard 1980; Raine 1983; Krohn et al. 1997), and because they are more vulnerable to potential predators without forest cover (Powell 1993). Furthermore, preferred prey species may be more abundant or vulnerable in areas with higher canopy closure (Buskirk and Powell 1994).
Several studies have shown that fishers are associated with riparian areas (Buck 1982; Jones 1991; Aubry and Houston 1992; Seglund 1995; Dark 1997; Zielinski et al. 1997c; Zielinski et al. in press 2003b, in press 2003a). Riparian forests are in some cases protected from logging and are generally more productive, thus having the dense canopy closure, large trees and general structural complexity associated with fisher habitat (Dark 1997). According to Seglund (1995), riparian areas are important to fishers because they provide important rest site elements, such as broken tops, snags, and coarse woody debris.
Composition of Home Ranges
Mazzoni (2002) measured habitat composition within the home ranges
of 11 fisher in the southern Sierra Nevada. Home range areas averaged 24.8 percent
[[Page 18774]]
coverage by ``latesuccessional'' (greater than 50 percent canopy
cover, greater than 24 in (61 cm) diameter) conifer forest habitat
(range 15.0 to 32.1 percent). The mean percent of home range area with
dense (greater than 50 percent canopy cover) conifers of all sizes was
53.6 percent (range 34.9 to 76 percent). Also in the southern Sierra
Nevada, Zielinski et al. (in press 2003a) found that home ranges of 12
fishers consisted of 12.8 percent (SD=10.9) large tree (greater than 24
in (61 cm) ) conditions. Intermediate tree size classes (1224 in dbh),
dense (greater than 60 percent) canopy closure, and Sierran Mixed
Conifer forest type composed the greatest proportion of the home ranges studies (60.7, 66.3, and 40.1 percent, respectively).
In the North Coast Range of northern California, Zielinski et al. (in press 2003a) found that home ranges of nine fishers were dominated by midseral Douglasfir and white fir (42.8 percent); home ranges included 14 percent (SD=13.36) latesuccessional Douglasfir on average and 13.97 percent true fir (SD=10.23), on average.
Resting and Denning Habitat
Powell and Zielinski (1994) and Zielinski et al. (2003b) 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 woodydebris, dense canopy closure and multiplecanopy 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. in press 2003b).
Rest sites have structures that provide protection from unfavorable weather and predators. Fishers also use rest sites as protected locations to consume prey following a successful foraging bout (Zielinski, pers. comm.). Reuse of rest sites is relatively low (14 percent: Zielinski et al. in press 2003b), 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 SiteStand 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. in press 2003b). 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. in press 2003b). Seglund (1995) found that a majority of fisher rest sites (83 percent) were further than 328 ft (100 m) from human disturbance and Dark (1997) found that fishers used and rested in areas with less habitat fragmentation and less human activity. Characteristics of forest stands containing rest sites on industrial timberlands were similar to those reported elsewhere in northern California. Fishers in Shasta County used rest sites in stands of the largest tree size classes available, with mean canopy closure of 71 percent (Self and Kerns 2001).
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. 2003b). Tree size, age, and structural features are important characteristics of a rest structure. Zielinski et al. (in press 2003b) stated that rest structures in their study areas in the North Coast and the southern Sierra Nevada were among the largest diameter trees available, averaging 46.2, 47.2, and 27.2 in (117.3, 119.8, and 69.0 cm) for live conifers, conifer snags, and hardwoods, respectively. Most rest locations in the study areas of Zielinski et al. (2003b) were in cavities or broken tops of standing trees. 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. 2003b). Cavities in hardwoods were the most frequently used rest structure in the southern Sierra Nevada study area where Douglasfir is absent (37.5 percent of rest structures were in black oaks); and in the North Coast study area, Douglasfirs were the most frequently used species (65.6 percent) and black oaks were used less frequently (11.4 percent) (Zielinski et al. 2003b). Higley et al. (1998) found that fishers in their Klamath study area use live hardwood trees most frequently for resting (57.14 percent) followed by live conifer trees (26.29 percent), snags and logs (14.86 percenthardwoods and conifers combined) and the ground (1.71 percent). On managed industrial timberlands in northwestern California, fisher resting sites (N=35) were predominantly located on dwarf mistletoe in western hemlocks, large lateral branches and mammal nests in Douglasfirs, and cavities in cedars (Simpson Resource Company 2003). The majority of 34 rest sites described by Self and Kerns (2001) were located in mistletoe brooms in live Douglasfirs, whereas only 20 percent were in snags or hardwoods.
Natal and Maternal Dens
Most dens are found in live trees, and there is little evidence that den sites are reused over time (Campbell et al. 2000). The trees must be large enough for cavities that can be used for natal and maternal dens. Of 19 tree dens documented by Truex et al. (1998) across three study areas in California, the average diameter was 45 in (115 cm) for conifers and 25 in (63 cm) for hardwoods. Of 16 maternal and natal dens located on managed timberlands in northwestern California, nine were in cavities in hardwoods and seven were in conifer snags: diameters of den trees ranged from 24.6 in (62.5 cm) to 116 in (295 cm) (Simpson Resource Company 2003). According to Lewis and Stinson (1998), natal dens are most commonly found in tree cavities at heights of greater than 20 ft (6 m), while maternal dens may be in cavities closer to the ground so active kits can avoid injury in the event of a fall from the den. The mean height of natal and maternal dens found in British Columbia was 99 ft (26 m) above ground (Weir and Harestad 2003). The height of these dens may help prevent predation by the larger male fishers or by other species.
Foraging Habitats
Fishers in the Pacific States appear to be dietary generalists, and therefore, they may be flexible in their requirements for foraging habitat. Selection of foraging habitat may be driven by habitat relationships of primary prey species.
Several studies have characterized foraging habitat which, similar
to resting habitat, is often typified by characteristics associated
with mature and latesuccessional forests (Jones and Garton 1994; Zielinski et al. 1997c).
[[Page 18775]]
However, fishers have been found to use a broader range of successional
stages for hunting than for resting (Jones 1991; Heinemeyer 1993; Jones
and Garton 1994). Jones (1991) found that youngeraged forests appeared
suitable for hunting but were rarely used for summer resting; more
structurally complex forests seemed to have been preferred for both
activities, but simpler stand structures were used for hunting. In
their use of younger forests, fishers in Idaho still appeared to select
localities with higher availability of largediameter trees, snags, and
logs (trees over 18 in (47 cm) diameter, snags over 20 in (52 cm)
diameter, and logs over 18 in (47 cm)) relative to randomlylocated plots in the home range (Jones 1991).
Complex down woody material including large down logs, and multi layered vegetative cover are important habitat elements for fishers. Fishers are often detected at sites with higher amounts of downed logs than at random sites (Klug 1997; Slauson et al. 2003), and high volumes of coarse woody debris and structural complexity near the forest floor (Weir and Harestad 2003), at least in part because high structural diversity is associated with prey species richness and abundance (Slauson et al. 2003) and greater prey vulnerability to capture (Buskirk and Powell 1994). Shrubs also provide food for prey and for fishers in the form of fruits and berries. Slauson et al. (2003) found that sites in their study area where fishers were detected had higher shrub cover (4060 percent) than sites where they were not detected. Fishers may also avoid areas with too much low shrub cover because it may adversely affect the hunting success of fishers (Weir and Harestad 2003).
Conclusion
The key aspects of fisher habitat are best expressed in forest stands with latesuccessional characteristics. Fishers use habitat with high canopy closure, large trees and snags, large woody debris, large hardwoods, multiple canopy layers, and avoidance of areas lacking overhead canopy cover (Aubry and Houston 1992; Buskirk and Powell 1994; Buck et al. 1994; Seglund 1995; Klug 1996; Dark 1997; Truex et al. 1998; Mazzoni 2002; Weir and Harestad 2003; Zielinski et al. in press 2003b, in press 2003a). Fisher also occupy and reproduce in some managed forest landscapes and forest stands not classified as late successional that provide some of the habitat elements important to fisher, such as relatively large trees, high canopy closure, large legacy trees, and large woody debris, in secondgrowth forest stands (Klug 1997; Simpson Resource Company 2003). However, intensive management for fiber production on industrial timberlands does not typically provide for retention of these elements. It is unlikely that early and midsuccessional forests, especially those that have resulted from timber harvest, will provide the same prey resources, rest sites and den sites as more mature forests (Zielinski and Powell 1994).
Latesuccessional coniferous or mixed forests provide the most suitable fisher habitat because they provide abundant potential den sites and preferred prey species (Allen 1987). Forest structure of good quality fisher habitat should provide high diversity of dense prey populations, high vulnerability of prey to fishers, and natal and maternal dens and resting sites (Powell and Zielinski 1994). Younger forests in which complex forest structural components such as large logs, snags, and tree cavities are maintained in significant numbers, and which provide a diverse prey base, may be suitable for fisher (Lewis and Stinson 1998).
Distinct Population Segment
In a 12month finding, we must determine if (1) the petitioned action is warranted, in which case we would promptly publish a proposed rule to list the species; (2) the petitioned action is not warranted; or (3) the petitioned action is warranted but precluded by other higher priority listing activities. Under the Act, a species is defined as including any subspecies and any distinct population segment of a vertebrate species. To implement the measures prescribed by the Act and its Congressional guidance, we and the National Marine Fisheries Service (National Oceanic and Atmospheric AdministrationFisheries), developed a joint policy that addresses the recognition of DPSs of vertebrate species for potential listing actions (61 FR 4722). The policy allows for a more refined application of the Act that better reflects the biological needs of the taxon being considered, and avoids the inclusion of entities that do not require its protective measures. The DPS policy specifies that we are to use three elements to assess whether a population segment under consideration for listing may be recognized as a DPS: (1) the population segment's discreteness from the remainder of the species to which it belongs and (2) the significance of the population segment to the species to which it belongs. Our evaluation of significance is made in light of Congressional guidance that the authority to list DPSs be used ``sparingly'' while encouraging the conservation of genetic diversity. If we determine that a population segment meets the discreteness and significance standards, then the level of threat to that population segment is evaluated based on the five listing factors established by the Act to determine whether listing the DPS as either threatened or endangered is warranted.
Below, we address under our DPS policy the population segment of the fisher that occurs in the western United States in Washington, Oregon and California. The area for this DPS includes the Cascade Mountains and all areas west, to the coast in Oregon and Washington; and in California, the North Coast from Mendocino County north to Oregon, east across the Klamath (Siskiyou, Trinity, and Marble) Mountains, across the southern Cascade Mountains and south through the Sierra Nevada Mountains. The mountainous areas east of the Okanogan River in Washington and the Blue Mountains west to the Ochoco National Forest in eastern Oregon are not included in this DPS due to their geographical isolation from the remainder of the DPS.
Discreteness
Under our DPS policy, a population segment of a vertebrate species may be considered discrete if it satisfies either one of the following two conditions: (1) it is markedly separated from other populations of the same taxon as a consequence of physical, physiological, ecological, or behavioral factors (quantitative measures of genetic or morphological discontinuity may provide evidence of this separation); or (2) it is delimited by international governmental boundaries within which differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist that are significant with regard to conservation of the taxon in light of section 4(a)(1)(D) of the Act.
The proposed DPS is markedly separated from other fisher populations as a result of several factors. Native populations of the fisher in California and the reintroduced population in the southern Cascade Mountains of Oregon are physically isolated from the Canadian populations by over 200 miles (Weir 2003), given the northward contraction of the British Columbia population (Weir 2003) in Canada. Substantial information is available indicating the West Coast population is also physically separated from known populations of the fisher to the east.
The range of the fisher in Washington, Oregon, and California is
separated from the Rocky Mountains and the rest of the taxon in the central and eastern United
[[Page 18776]]
States by natural physical barriers including the nonforested high
desert areas of the Great Basin in Nevada and eastern Oregon, and the
Okanogan Valley in eastern Washington. At its extreme northern
(unoccupied) extent in northern Washington, the DPS is separated from
the western extension of the Rocky Mountains and associated ranges by
the Okanogan Valley, a distance of approximately 93 to 124 mi (150 to
200 km), which is well beyond the dispersal range for the species.
Other physical barriers that separate the West Coast population from
Rocky Mountain and eastern U.S. fisher populations include major
highways, urban and rural opencanopied areas, agricultural
development, and other nonforested areas. Fishers have a strong
aversion to areas lacking in forest cover or to crossing large rivers
that do not freeze in the winter (Powell 1993; Powell and Zielinski
1994; Aubry and Lewis 2003); these behavioral factors, along with the
other numerous barriers identified above, represent a significant
impediment to eastward or westward movement for the fisher.
We currently have limited information on dispersal distances of fishers in the western United States. However, studies conducted on fisher dispersal in the northeastern United States indicate that dispersal distances are relatively short (Arthur et al. 1993; York 1996). There is no evidence that fishers are successfully dispersing outside of known population areas in California and Oregon. This is possibly due to the extent of habitat fragmentation, developed or disturbed landscapes, and highways and interstate corridors (see dispersal section above).
Genetic information (Drew et al. 2003) indicates that the West Coast population of fisher originally colonized the Pacific states from British Columbia. The current range of fisher in British Columbia has been reduced and connection to fisher populations in the continental United States no longer exists (Weir 2003, BC Species and Ecosystems Explorer 2003). The fisher's present range in British Columbia has contracted northward from the international boundary by about 200 kilometers. (Weir 2003). Movement of fisher from British Columbia southward to areas occupied by the West Coast population is not possible based on lack of available habitat, habitat preferences, and dispersal behavior of the fisher.
The West Coast population also appears to be separated from other populations as a result of ecological factors, as they use forest types that differ in species composition, tree size, and habitat structure as compared to those used by fishers in other populations. The fisher is regarded as a habitat specialist in the western United States (Buskirk and Powell 1994), occurring only at mid to lower elevation in mature conifer and mixed conifer/hardwood forests characterized by dense canopies and abundant large trees, snags, and logs (Powell and Zielinski 1994). In contrast, fishers in the northeastern United States and the Great Lakes region inhabit areas with a large component of deciduous hardwood forest containing American beech (Fagus grandifolia), sugar maple (Acer saccharum), and other broadleaf species (Powell and Zielinski 1994). The majority of conifer forest habitat in Canada is characterized as boreal forest, which is different from the relatively dryer environmental conditions associated with Washington, Oregon, and California. In the Rocky Mountains of north central Idaho, certain allconifer habitat types which include grand fir and Engelmann spruce appear to be important to, and preferentially selected by fishers (Jones 1991).
With regard to physiological differences, the fishers in the native northern California population are significantly smaller in size (based on condylobasal length) than fishers from western and central Canada (Hagmeier 1959; Zielinski et al. 1995; Aubry and Lewis 2003.
The West Coast population of the fisher is also delimited to the north by the international governmental boundary between the United States and Canada because of differences in control of exploitation, management of habitat, conservation status, and regulatory mechanisms that may be significant with respect to section 4(a)(1)(D) of the Act. Canada has no overarching forest practices laws governing management of its national lands. In contrast, lands within the National Forest System in the United States are considered under the National Forest Management Act of 1976, as amended (16 U.S.C. 1600), and associated planning regulations. The fisher is covered by British Columbia's Wildlife Act which protects virtually all vertebrate animals from direct harm, except as allowed by regulation (e.g., hunting or trapping). The fisher is designated as a Class 2 furbearer in British Columbia and, as such, can be legally harvested by licensed trappers under regional regulations. However, the fisher was reclassified to the Red List in British Columbia in 2003 with a provincial conservation ranking of ``S2,'' as assigned by the British Columbia Conservation Data Centre to ``score'' the risk of extinction or extirpation (BC Species and Ecosystems Explorer 2003). The Red List designation means that the species is considered imperiled at the provincial level. The change in the fisher designation was the result of an estimated provincial population of fewer than 3,000 individuals and habitat loss due to logging, hydroelectric development and other land use changes (BC Species and Ecosystems Explorer 2003). Although the change in Red List designation for the fisher in British Columbia carries no legal implications, trapping seasons for it have been closed until new information is collected that indicates the population is secure (BC Ministry of Land, Water, and Air Protection 2003). Beyond this voluntary closure of the trapping season, the fisher carries no protected status in British Columbia. Trapping the species has been prohibited for decades in Washington, Oregon, and California (Lewis and Stinson 1998). For the reasons stated above, we believe that these factors collectively play a role in delimiting the northern DPS boundary along the international border with Canada from the Cascade Mountains west to the Pacific Ocean.
Based on the available information on fisher range and distribution, we conclude that the West Coast population of fisher is distinct and separate from other fisher populations in the United States and meets the requirements of our DPS policy for discreteness. The West Coast population of fisher is separated from fisher populations to the east by geographical barriers and to the north by habitat availability; it is further delineated by the international boundary with Canada, within which there are differences in control of exploitation, conservation status, and regulatory mechanisms that are significant to its conservation.
Significance to the Species
Under our DPS policy, once we have determined that a population
segment is discrete, we consider its biological and ecological
significance to the larger taxon to which it belongs. This
consideration may include, but is not limited to, the following
factors: (1) Persistence of the discrete population segment in an
ecological setting unusual or unique for the taxon; (2) evidence that
loss of the discrete population segment would result in a significant
gap in the range of the taxon; (3) evidence that the population segment
represents the only surviving natural occurrence of a taxon that may be
more abundant elsewhere as an introduced population outside its
historical range; and (4) evidence that the discrete population segment differs markedly
[[Page 18777]]
from other populations of the species in its genetic characteristics.
Significance is not determined by a quantitative analysis, but instead
by a qualitative finding. We have found substantial evidence that the
West Coast DPS of the fisher meets two of the significance factors and
is supported by a third significance factor, and we have described them below.
Fishers in the West Coast population persist in an ecological setting that is unusual in comparison to the rest of the taxon, with a different climate, topography, and habitat than that found in the majority of its range. 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. The Pacific coast's wet winter followed by a dry summer is unique in comparison to climate types in the east and Canada, and produces distinctive sclerophyll forests of hardleaved evergreen trees and shrubs (Smith et al. 2001). This climate is characterized by mild, wet winters and warm, dry summers (Bailey 1995), while the climate in the animal's range in the Rocky Mountains consists of cold winters and cool, dry summers, and in the Great Lake States, eastern Canada, and the northeast United States it is characterized by cold winters, and warm, wet summers. 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. Releases of eastern fishers into western forests have generally been unsuccessful; Powell and Zielinski (1994) state that, ``Roy's (1991) results [unsuccessful attempts to reintroduce Minnesota fishers to Montana] indicate that many fishers from eastern North America may lack behaviors, and perhaps genetic background, to survive in western ecological settings.'' The repeated introductions of fishers from British Columbia and Minnesota to the southern Cascade Mountains of Oregon (from 1960s to 1980s) have resulted in an apparently stable, but small population there; however, the species is not expanding and dispersing from the areas into which it was introduced.
The loss of the West Coast DPS of the fisher would eliminate the entire southwest portion of the fisher's North American range. Additionally, the West Coast DPS 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. Based on figures from Weir (2003), the total range of the fisher in North America has been reduced approximately 33 percent in geographical area since the 1600s. This reduction is most apparent in the fishers southern and western rangelargely in the United States. Based on our review of Lewis and Stinson's (1998) maps (modified from Gibilisco 1994), these are three of only six or seven remaining areas occupied by fishers in the United States. Although these maps consider a large area of Canada to be within the 1994 range of the fisher, distribution has diminished in some areas of southeastern Ontario and Quebec, in the prairie provinces (Alberta, Saskatchewan, and Manitoba), and in the western United States (Gibilisco 1994); and because of the lack of inventories for the species in Canada, it is not known to what extent the range in Canada is occupied. Additionally, the populations in the southern Sierra Nevada and northern California/southern Oregon appear to be the only native populations of the fisher remaining in the west (Truex et al. 1998; Aubry et al. in press 2003; Drew et al. 2003), and are ``the only populations that have not been augmented with individuals (and genes) from other regions'' (Zielinski et al. 2003b).
As stated earlier (see distribution section), the extent of area known to be currently occupied by fishers in Washington, Oregon, and California is roughly 20 percent of their historical extent in these States. 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, recognizing that the historical range was not continuously occupied spatially or temporally, and that the present range we identify is also not occupied continuously nor is all of the historical habitat still available, especially in the midwest and east.
The extinction of fishers in their west coast range would also result in the loss of a significant genetic entity, since they have been described as being genetically distinct from fishers in the remainder of North America. More specifically, native fishers in California have reduced genetic diversity compared to other populations (Drew et al. 2003). Additionally, the extant native populations in California share one haplotype that is not found in any other populations (Drew et al. 2003).
Quantitative measures of genetic discontinuity indicate that there is no naturally occurring genetic interchange with the California fisher populations. Based on genetic evidence, and supported by paleontological and archeological evidence, Wisely et al. (in litt. 2003) theorize that fishers probably colonized the Pacific peninsula from the north, not the east. The fisher was once distributed throughout much of the dense coniferous forests in British Columbia, Washington, Oregon, and California (Drew et al. 2003). This historical connectivity among populations along the Pacific Coast is evidenced by the presence of British Columbia haplotypes in museum specimens from California and Washington (Drew et al. 2003). The historical continuity in fisher distribution no longer exists, as discussed above. Genetic variation shows the Oregon southern Cascade population is a reintroduced population descended from fishers translocated to Oregon from British Columbia and Minnesota (Drew et al. 2003). There is evidence that there has been no genetic interchange between the native northern California/southwestern Oregon Siskiyou population and the reintroduced southern Cascade Oregon population (Aubry et al. in press 2003).
Conclusion
We have evaluated as a DPS the population of fishers in the West
Coast range and have addressed the elements our policy requires us to
consider in deciding whether a vertebrate population may be recognized
as a DPS and considered for listing under the Act. In assessing the
population segment's discreteness from the remainder of the taxon, we
have described the factors separating it from other populations. We
considered distributional, ecological, behavioral, morphological, and
genetic information, information from status surveys, and geographical
and biogeographical patterns, and have concluded that this population
segment is discrete under our DPS policy. In assessing the population
segment's significance to the taxon to which it belongs, we have
considered the geographical area represented by the western DPS, its
genetic distinctness from fisher populations in the central and eastern
United States, its unique ecological setting, and other considerations
and factors as they relate to the species as a whole. We conclude that loss of the species from the west
[[Page 18778]]
coast range in the United States would represent (1) a significant gap
in the species' range, (2) the loss of genetic differences from fisher
in the central and eastern United States, and (3) the loss of the
species from a unique ecological setting. Therefore, as the population
segment meets both the discreteness and significance criteria of our
DPS policy, it qualifies as an entity that may be considered for
listing. We now evaluate its status as endangered or threatened. In
making this determination, we evaluate the factors enumerated in section 4(a)(1) of the Act (16 U.S.C. 1533 (a)(1)).
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533), and implementing regulations at 50 CFR 424, set forth procedures for adding species to the Federal endangered and threatened species list. In making this finding, information regarding the status and threats to this species in relation to the five factors in section 4 of the Act is summarized below.
Factor A. The Present or Threatened Destruction, Modification, or Curtailment of the Species' Habitat or Range. Vegetation management activities such as timber harvest and fuels reduction treatments, standreplacing fire, largescale forest disease outbreaks or insect infestations (e.g., pine beetle), and development can destroy, alter, or fragment forest habitat suitable for fishers.
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. Based on northeastern fisher home range sizes, Allen (1983) estimated that a minimum of 161 km2 (39,780 ac) of potentially suitable and contiguous habitat must be present before an area can sustain a population of fishers. However, fisher populations in western forests may need even larger areas because male home ranges in northern California have been reported to be as large as 128 km2 (Beyer and Golightly 1996). A habitat suitability model developed in British Columbia figures that a minimum of 259 km5 of contiguous habitat is required for fisher transplant attempts (Apps 1996 as cited in Craighead et al. 1999).
Fishers use large areas of primarily coniferous forests with fairly dense canopies and large trees, snags, and down logs; vegetated understory and large woody debris appear important for their prey species. Fishers in the Pacific Northwest use latesuccessional forest more frequently than the early to midsuccessional forests that result from timber harvest (Aubry and Houston 1992; Buck et al. 1994; Rosenberg and Raphael 1986). Elimination of latesuccessional forest from large portions of the Sierra Nevada and Pacific Northwest (Morrison et al. 1991; Aubry and Houston 1992; McKelvey and Johnston 1992; Franklin and FitesKauffman 1996) has probably significantly diminished the fisher's historical range on the west coast (Lewis and Stinson 1998).
Several studies have found sharp declines in latesuccessional/old growth forests (Beardsley et al. 1999, Bolsinger and Waddell 1993, the Report of the Forest Ecosystem Management Assessment Team (FEMAT) 1993, Franklin and FitesKaufmann 1996, Morrison et al. 1991, Service 1990). Old growth comprised about 50 percent of the forests of Washington, Oregon, and California in the 1930s and 1940s, but made up less than 20 percent of those forests in 1992 (about 10.3 million ac; 41,683 km \2\) (Bolsinger and Waddell 1993).
Franklin and FitesKaufman (1996) find that forests with high late successional/oldgrowth structural rankings are now uncommon in the Sierra Nevada of California (8 percent of mapped area). Mixed conifer forests are a particularly poorly represented forest type as a result of past timber harvesting, and key structural features of late successional/oldgrowth forests, such as largediameter trees, snags, and logs, are generally at low levels (Franklin and FitesKaufman 1996). The loss of structurally complex forest and the loss and fragmentation of suitable habitat by roads and residential development have likely played significant roles in both the loss of fishers from the central and northern Sierra Nevada and the fisher's failure to recolonize these areas (USDA Forest Service 2000).
Within the Northwest Forest Plan area, 60 to 70 percent of the forested area of the region was historically dominated by late successional and oldgrowth forest conditions. Most of the forest (perhaps 80 percent) probably occurred in relatively large contiguous areas (greater than 1000 ac; 4 km \2\) (Bolsinger and Waddell 1993, USDA Forest Service and U.S. Department of Interior Bureau of Land Management (USDI BLM) 1994a). Franklin and Spies (1986) estimated that 15 million ac (60,703 km \2\) of oldgrowth forest existed west of the Cascade Mountains in Oregon and Washington in the 1800s, and only about 5 million ac (20,234 km \2\; 33 percent) remain. FEMAT (1993) reports the status of forests in several regions: private and State lands within western Washington and western Oregon Cascades have mostly been harvested, whereas Forest Service and Bureau of Land Management lands (BLM) still include significant areas (albeit highly fragmented) of late successional/oldgrowth forest; the Klamath Provinces of southwestern Oregon and northwestern California have forests that are highly fragmented by timber harvest and natural factors (poor soils, dry climate, wildfires); the southern end of the Cascades Range in Oregon extending into California has forests that are highly fragmented due to harvest activities and natural factors.
The NWFP states that fisher populations are believed to have declined on Federal lands in oldgrowth habitat for two primary reasons: (1) Loss of habitat due to forest fragmentation resulting from clearcutting, and (2) the removal of large down coarse woody debris and snags from the cutting units (USDA Forest Service and USDI BLM 1994). Fishers in the eastern Klamath area of northern California hav
FOR FURTHER INFORMATION CONTACT
Jesse Wild or Arnold Roessler at the above address (telephone: 916/4146600; fax: 916/4146710; electronic mail: fisher@fws.gov). In the event that our Internet connection is not functional, please submit your comments by the alternate methods mentioned above.