The fisher is BLUE-listed because populations are believed to have declined recently over much of their range. Populations are particularly susceptible to over-harvest by trapping, and are sensitive to habitat change through forest harvest, regeneration and stand tending. No provincial population estimate exists for the fisher, but it is legally harvested for its pelt in some areas of the province.
Fishers inhabit forested habitats, particularly those with mixed habitat and structural classes, edges and riparian areas. In the mid-western and northeastern United States, the fisher occurs in extensive mid-successional to mature forests, but in western North America they are more associated with late successional forests. Aspects of forest structure (see "Habitat requirements"), are likely more important determinants of distribution and habitat use than are forest types.
In B.C., the fisher is often closely associated with riparian and dense wetland forest types. It generally stays in or near forests with canopy closure of at least 30%. Resting and maternal denning sites are located in these habitats in large, mature and declining trees. Winter resting sites are associated with large coarse woody debris (CWD) and large spruce with spruce broom rust. Maternal den sites in B.C. are almost entirely found in large declining cottonwood, although they will likely use other tree species. Availability of suitable maternal and resting den sites may be limiting factors for the population.
The fisher is a generalist predator. Prey include porcupine, snowshoe hare, squirrels, mice, voles, shrews, birds and carrion. In central B.C. (dry SBS), 55% of their diet is comprised of snowshoe hare, squirrels and mice. Most foraging in winter occurs above the snow layer, and as such snow conditions likely influence foraging and distribution patterns. Summer foraging is strongly associated with CWD. Primary prey species are associated with abundant CWD and understorey shrub cover.
The reported home range of fisher ranges from 4-32 km2 for females (mean 15 km2) and
19-79 km2 for males (mean 40 km2). Because of their relatively large home range, 600 km2 has been suggested as a minimum area necessary to manage for viable populations.
Although fisher occur throughout B.C., they are rare in coastal ecosystems. Preferred habitat resembles that found in SBS, SWB and BWBS biogeoclimatic zones. The fisher is currently absent, but was historically present, in the CCM, EPM, MCR and BRR ecosections of the Southern Interior Mountains (SIM) ecoprovince.
COM: KIR, NAB, NPR
SIM: BOV, QUH, SHH, CAM, CCM, EPM, MCR, NKM, FRR, BRR, SFH, NPK, BBT, UFT
SOI: LPR, PAR, SCR, SOH, HOR, OKR, NOH, NTU
NBM: CAR, KEM, SBP, STP, TEP, TUR, HYH, LIP, MUF, EMR, WMR, TEB, THH
BWBS, CWH, ESSF, ICH, IDF, MH, MS, SBPS, SBS, SWB
Broad ecosystem units of high value are CR, IH, SD, SF and RR (interior locations only). Those of medium value are BA, BP, DF, DL, ER, HB, IS, SA and SL.
Fisher forage within many structural stages. Structural stages 1a (non-vegetated), 1b (sparse), 2 (herb), 3a (low shrub), and 3b (tall shrub) are not utilized during winter. They may be used in other seasons providing sufficient forage and security cover is present. Most habitat use is associated with structural stages 6 (mature forest) and 7 (old forest) where structural characteristics of older forests are most developed. Resting and maternal denning habitat is typically associated with structural stages 6 and 7, and key features are availability of CWD, large wildlife trees and canopy cover in winter. Fisher will forage in a wider range of structural stages (particularly in summer) and habitat use may be influenced by population cycles of major prey species.
Riparian and riparian-associated habitats, particularly those with large spruce trees (minimum 25 cm dbh; recommended 40 cm dbh) with broom rust, and large (75 cm dbh) cottonwood or fir trees, are used as resting and maternal denning sites.
Coarse woody debris (decay class 2-6) is important for resting sites and as habitat for prey species. A continued supply of decay class 2 logs are required to provide denning sites. In the SBS zone maternal den sites are predominantly in large cottonwoods in cavities created by broken branches.
Riparian-riparian and riparian-upland connectivity is also important. The fisher uses habitats with generally greater than 30% canopy cover and a productive understorey that supports a variety of small and medium-sized prey species.
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forest carnivores: American marten, fisher, lynx and wolverine in the western United States. L.F. Ruggiero, K.B. Aubry, S.W. Buskirk, L.J. Lyon and W.J. Zielinski (eds.). USDA For. Serv., Ft. Collins, CO. Gen. Tech. Rep. RM-254. pp. 38-73
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central British Columbia. Simon Fraser Univ., Burnaby, B.C. MSc thesis.