This is an exhaustive literature review and management strategy to restore the fisher in the western United States.

Part I is a review of fisher biology and management. Part II is an adaptive management strategy. Parts III and IV are an annotated bibliography and a selection of reference papers.

The focus of this summary will be the adaptive management strategy (Part II), since it is unique among the fisher literature and directly relevant to the purpose of this information clearinghouse. Some statements from the executive summary and review (Part I) are excerpted here as well.

Executive Summary

Population and metapopulation status in western habitats (p. iv)
"In the western U.S., fishers are limited to the peninsular mountain ranges of the Pacific Coast and Rocky Mountains, forming the southern margins of a larger continental distribution. The peninsular populations may be acutely susceptible to extinction because of their location at the margins of their geographic distribution.
Fishers have been shown to selectively use habitats; it is likely these habitats are patchily distributed in modern landscapes and extant populations of fishers are widely-spaced and fragmented. Little is known of the dispersal and colonization capabilities of fishers, or the degree in which present populations are inter-related."

Management Strategy (pp. iv-v)
The authors summarize their management strategy for fishers at five different geographic scales, for example:
"At the largest, or continental landscape unit, the overall goal of the management strategy is to demographically and genetically link the Pacific and Rocky Mountain populations to the Canadian population…"

Part I: Fisher Biology and Management

Figure 1 shows the distribution of fisher observations and potential habitat in the western U.S. (p. 4).

Trapping (p. 11)
"Fishers are susceptible to trapping… and are frequently trapped in sets made for other furbearers… In Idaho, where fishers are protected, Luque (1983) estimated that at least 163 animals were inadvertently trapped over a 5-year period in sets made for marten, coyote and possibly bobcat. In Montana, approximately 10% of radio-tagged reintroduced fishers were killed in traps set for coyote and marten (Roy 1991, Heinemeyer 1993).
Fisher populations are sensitive to trapping pressure, as even light trapping pressure may cause local extinction (Powell 1972, 1982)… Jones (1991) speculated that in Idaho, incidental captures in sets designed for other furbearers may be limiting population growth…"

Table 5 lists all known fisher reintroduction attempts (p. 21).

Population and Metapopulation Status in Western Habitats (pp. 24-25)
"… The greatest longterm risk to the fisher in the western United States is probably population extinction due to isolation of small populations."

Part II: Adaptive Management Strategy

Introduction
"… The continuation of current forest management practices will likely result in further fragmentation of mature and older forests and increased isolation of smaller parcels of potential habitats within a matrix of unsuitable and/or unproductive habitats across the landscape… As forest management activities proceed, the landscape is increasingly fragmented by roads. Consequently, trapping access and efficiency is improved, and the proportion of the landscape and fisher populations relatively secure from trapping decreases." (p. 26)

"The overall goal of this management strategy is to maintain fisher populations with high persistence probabilities across their historic range throughout western North America. This goal may be achieved through meeting the following objectives:
1. Manage for the continued distribution of fishers throughout their current range.
2. Manage habitats so that subpopulations of fishers have the opportunity to interact demographically, thereby minimizing the risks to long-term viability to the metapopulation.
3. Manage for the restoration of habitats and populations within the fishers' historic range.
4. Monitor and conduct research to evaluate whether the goals and objectives are being met and to facilitate adaptive management." (p. 28)

Management Strategy

Continental

"For all practical purposes, the Pacific and Rocky Mountain populations may have been (and still are) genetically isolated by geographic distance, and probably by physical and ecological distances (see Chesser 1983 for definitions). Presently, the two populations are undoubtedly genetically and demographically distinct since fishers have been extirpated in southern British Columbia." (p. 29)

Physiographic Region

"1. Minimize human-induced barriers to dispersal in sensitive-linkage zones.. [includes mortality factors and habitat-alteration activities]
2. Conduct genetic studies to establish the variability within and among identified metapopulations…
3. Identify and prioritize potential recolonization or augmentation areas…
4. Maintain the potential for dispersers to move across sensitive-linkage zones… allow for the successful dispersal of at least one individual every 2 years to maintain genetic diversity… limit road densities (accessible to trappers) to 0.2 km/km2 (0.3 mi/mi2) or less. This would approximate one open road bisecting the entire length of an average size male homerange in Idaho. An alternative to open road management would be to restrict furbearer trapping within the linkage zone, at least during the dispersal period (i.e., October through March).
5. Prevent (or mitigate for) the creation of induced ecological barriers. Clearings (i.e., <30% canopy cover) greater than 500 ft wide should not bisect sensitive-linkage zones. If clearings must bisect a sensitive zone, then mitigate by managing a stepping-stone "bridge" of cover patches consisting of trees >5 m tall. Cover patches should be at least 0.2 ha in size and be within 30 m of each other. These habitat "bridges" should be established at the frequency of at least one per mile." (p. 30)

"Physical barriers identified include large water bodies, greater than 460m (500 ft) [sic] wide, that remain unfrozen throughout the winter… Using the Columbian and Snake Rivers as two physical barriers, in conjunction with ecological barriers identified on the habitat map, 7 potential metapopulations in the western United States were identified… Twelve sensitive-linkage zones were also identified at this scale [listed by name]…" (pp. 31-32).

Physiographic Area

"1. Maintain the short-term viability… of 80% or more of all subpopulations within a single metapopulation.
2. At least 80 percent of all subpopulations should be linked to other subpopulations by a functional corridor. Subpopulations should be within 29 km (18 miles; 75% of the maximum dispersal distance… of each other)…
3. Manage a central 'core' or 'reservoir' subpopulation…
4. Establish a refuge within the core subpopulation protected from direct or incidental trapping mortality…" (p. 32)

"Corridors longer than 10 km should provide the resources to allow for temporary residency and should contain some preferred resting and foraging habitats. Generally, the longer the linkage zone, the wider it should be." (p. 32)

"… it will be assumed that refugia within core populations should support at least 14 adult females and 7 adult males. Within the Northern Rocky physiographic region, this size is estimated to be 600 km2." (p. 33)

"Absolute barriers probably exist if unsuitable habitat patches exceed 300 m wide, or if avoided habitats exceed 2.5 km wide. Semipermeable barriers may exist when suitable, but avoided habitats are greater than 100 m, but less than 2.5 km wide. Major highways having right-of-ways greater than 60 m wide would also be considered a semipermeable barrier. Temporal barriers consist of early-successional stages… avoided by fishers of suitble forested habitats exceeding 100 m wide…" (pp. 33-34)

Guidelines (p. 34):
- linkages less than 16 km long should be at least 2.5 km wide; linkages more than 16 long should be at least 5 km wide;
- linkages should follow drainage bottoms;
- no more than 25% of the linkage should be an opening (i.e., <30% canopy cover);
- road densities within linkages open to trappers should be no more than 0.2 km/km2 (0.3 mi/mi2) if linkage is longer than 5 km;
- trapping of furbearers should be prohibited within fisher refugia;
- ~65-75% of fisher refugia should be late-successional forest (120 years and older), the remainder should contain 10-25% young forest, and 10-25% pole/sapling or younger (less than 50 years).

Major Watershed

"Classify lands as to their trapping-vulnerability risk…
a. For areas having fisher or marten trapping seasons: Low risk = <0.25 mi/mi2; Moderate risk = 0.25-1.00 mi/mi2; High risk = >1.00 mi/mi2.
a. For areas with trapping seasons for other terrestrial furbearers: Low risk = <0.75 mi/mi2; Moderate risk = 0.75-2.00 mi/mi2; High risk = >2.00 mi/mi2." (p. 36)

"Classify major watersheds as a Primary or Secondary Fisher Conservation Area (PFCA or SFCA, respectively)… PFCAs are defined here as having at least 50% suitable or preferred habitat… well-distributed and interconnected… SFCAs should have a minimum of 30% suitable or preferred habitat…" (p. 36)

"[Within PFCAs] no more than 20% of the watershed should be… 'high risk' to trapping… at least 40% of the watershed should be… 'low risk.' At least 50% of the watershed should be at least 2.5 km from any road or trail accessible to motorized trapping access…

[Within SFCAs] no more than 30% of the watershed should be… 'high risk' to trapping… at least 30% of the watershed should be… 'low risk.' At least 30% of the watershed should be at least 2.5 km from any road or trail accessible to motorized trapping access…" (p. 37)

"All major watersheds should be interconnected by functioning corridors comprised of habitat suitable for travel. The dendritic pattern of forested stream courses provides preferred travel networks, and are used extensively by fishers… Forested saddles, linking adjacent major drainages, may serve as potential travel routes, and may be especially important for fisher movements. A canopy cover of at least 40% should be maintained in critical saddles. Gaps (i.e., areas having less than 30% canopy cover) within potential travel corridors should not exceed 100 m." (p. 38)

Subdrainage

Guidelines (pp. 38-39)
- High Quality Subdrainage: maintain 65-75% mature/old forests, 10-25% young and pole/sapling classes; at least 80% of patches interconnected by travel corridors of closed canopy forest (i.e., >40% canopy cover); Mature and old-growth should be at least 50 ha (125 ac) with at least 75% of their perimeter adjacent to forest (pole stage or older, >40% canopy cover).
- Moderate Quality Subdrainage: maintain at least 40% mature/old forests; at least 60% of patches interconnected by travel corridors of closed canopy forest (i.e., >40% canopy cover); Mature and old-growth should be at least 32 ha (80 ac) with at least 50% of their perimeter adjacent to forest (pole stage or older, >40% canopy cover).
- Low Quality Subdrainage: maintain 30-40% mature/old forests; at least 40% of patches interconnected by travel corridors of closed canopy forest (i.e., >40% canopy cover); Mature and old-growth should be at least 24 ha (60 ac) with at least 30% of their perimeter adjacent to forest (pole stage or older, >40% canopy cover).

Stand

Guidelines: (pp. 40-41)
- Only uneven-aged management should be permitted in fisher habitat… openings should not exceed 0.4 ha (1 acre)
- Retain large diameter trees as rest sites
- Stands within riparian areas, including any stands within 30 m (100 ft) of water should only be treated using uneven aged silvicultural prescriptions… groups of trees taken should be no larger than 0.1-0.2 ha; at least 70% canopy cover should be retained
- With uneven-aged management:
- Retain at least 12 trees/ha, greater than 46 dbh…
- Retain >50-100 tons/ha of large diameter logs
- Retain log decks and some slash piles (1 per 2 ha)
- Do not precommercially thin more than 60% of regenerated stands; leave patches (at least 1 ha) distributed throughout the unit

Table 7 (p. 41) shows desired sizes and abundance of live trees, snags, and logs for fisher habitat in the northern Rockies (from Jones 1991).