The fisher (Martes pennanti) may be one of the most inappropriately named mammals. The fisher neither fishes nor eats fish. Its Chippewayn name, "tha cho," which means "big marten," is perhaps a better name, because like its smaller cousin the marten, the fisher eats small mammals, birds and carrion. Two-to-three times the size of the marten, the fisher is well adapted to climbing trees and does so frequently, but it is more at home on the ground.

The fisher is a member of the Mustelidae, or weasel family which also includes wolverines and martens. The fisher inhabits dense forests with extensive overhead canopy and usually avoids open areas. In the west, the fisher requires mature mesic (wet) forests in which to live. The fisher dens in hollow trees and logs, and seeks shelter during the winter in logs, brush piles, and snow dens. The fisher's beautiful dark brown pelt, often with a creamy patch on the throat, is highly valued by trappers.

Historically, the fisher was found in the northern forests throughout North America. Due to excessive trapping and logging, the fisher was nearly extirpated from most of the United States by 1930. Closed trapping seasons, regeneration of many logged-over forests, and reintroduction programs have since allowed the return of fishers to some of their old habitats; but populations have never recovered fully in the Rocky Mountains or the Pacific Northwest and are now at such critically low numbers that the fisher is threatened with extinction.

Fishers are generalized predators, but their main prey is herbivores such as mice, porcupines, squirrels, snowshoe hares, birds, shrew and sometimes other carnivores. The fisher serves a vital role in predator-prey relations in the forest ecosystem. For one, the fisher preys heavily on porcupines. The importance of maintaining this predator-prey relationship became apparent when fisher populations were drastically reduced in the early 1900's. With fisher numbers down, porcupine populations, and therefore damage to trees, increased. Fishers have been favored by lumbermen to help prevent tree damage by porcupines.

They are solitary hunters and will occasionally feed on fruits and berries. Active and speedy tree climbers, they are active both day and night, and have also been known to swim. Breeding occurs late winter to early spring with 1-5 kits being born per liter. Denning occurs in hollow trees and logs.

Like the wolverine and the lynx, the fisher usually avoids humans. The same developments that threaten these other carnivores road building, logging, trapping and other human exploitations - continue to threaten the fisher.

Their home range can vary from 12-30 km in diameter and 100-800 km in area. Preferred habitat includes "boreal", or evergreen forests that develop in areas with long, severe winters. Fishers enjoy dense forests with extensive overhead canopy and usually avoids open areas.