The fisher is a mid-sized carnivore, the second largest member of the weasel family in Pennsylvania; the river otter being the largest. Fisher are characterized by a well-furred long body, short legs, and a full tail that comprises about one third of its total length. While mostly dark to chocolate brown, fur on the tail, legs and rump is usually black, whereas fur on the back and shoulders is grizzled with gold and silver and enhanced by tricolored guard hairs. White areas or “patches” are common and are most frequently found in the genital areas as well as under the forelimbs. The face is triangular with wide and rounded ears. Fisher eyes have a horizontal oval pupil that produces a bright green eyeshine at night. Fishers have five toes on each paw and sharp, curved, semi-retractable claws.
The fisher is the largest member of the genus Martes, and males are considerably larger than females. Adult males weigh seven to 15 pounds; adult females from four to nine pounds. The heaviest fisher reported was a male from Maine that weighed 20 pounds. Males are longer than females, ranging from 35 to 48 inches; females range from 30 to 37 inches. Fisher achieve adult length within about six months, but continue to gain weight for several years.
Common names of the fisher include black cat, fisher cat, tree otter, tree fox, fisher weasel, pekan, and Oochik (Cree), which early fur traders pronounced as “wejack”. “Fisher” is the most frequently used common name and is thought to have originated from the fisher’s resemblance to a European polecat named “fichet.”
In the most general sense, fisher occupy forests with abundant downed woody debris or other structure on the forest floor. Fisher are generally believed to avoid areas lacking overhead cover, but the degree to which fisher will tolerate varying levels of forest fragmentation and human encroachment has not been well studied. During recent decades, fisher populations have expanded into highly fragmented, human altered forest ecosystems throughout many areas of the northeast, including Pennsylvania.
Despite its name, fisher rarely consume fish or other aquatic prey. Fisher are renowned for their ability to prey upon porcupines, and are unique among forest carnivores in that they are well adapted to forage effectively within the forest canopy as well as on the forest floor. Fisher are opportunistic and their diet is diverse, including small mammals, reptiles, insects, fruits and fungi. As consumers of fruits of shrubs and trees, primarily during summer, fisher serve as mammalian seed dispersers in forest ecosystems. Small mammals such as squirrels, chipmunks and mice are thought to be dominant prey sources for fisher in Pennsylvania during most seasons. There is evidence of fisher predation on white-tailed deer, but the frequency and effects of such predation are thought to be limited.
Female fishers give birth to one to six cubs from late February to May, with most litters produced during late March and early April. Female fishers cycle into estrous and usually breed seven to 10 days after parturition, but embryonic development does not begin until the following January or February. The gestation period is approximately 40 days. Both males and females reach sexual maturity by one year of age. Natal den sites are generally tree cavities high above the forest floor.
Young are born completely dependent on maternal care, with their eyes and ears closed, and are immobile until about three weeks of age. Juveniles open their eyes at six to eight weeks, deciduous teeth erupt at six weeks, and canines erupt at seven to nine weeks of age. Fisher weigh less than two ounces at birth and reach one pound by 40 to 50 days of age. The pelage of juveniles has been described as silver-gray until three to four weeks of age, turning to the characteristic chocolate brown thereafter. At 10 to 12 weeks of age, kits are completely chocolate brown and exhibit the tricolored guard hairs characteristic of adults. At four months of age, fishers are efficient at attacking the head and neck region of small prey. Juvenile fishers are generally intolerant of littermates by five months of age.
Fisher in Pennsylvania
Historic data suggest that fishers were distributed throughout most of Pennsylvania prior to intensive deforestation during the nineteenth century, but actual distribution and relative abundance back then is largely unknown. Fisher likely occurred at varying densities throughout most forested regions, with the possible exception of the far southeastern counties. Historic accounts also suggest that fisher populations initially began to decline in southwestern Pennsylvania due to early colonial development. Subsequent declines occurred steadily as forest habitats were cleared. The last remnant populations were believed to have been in Clearfield, Elk, Cameron, Clinton, Potter and Sullivan counties. Historic reports of fur dealers and shippers suggest that prior to fisher extirpation, relatively few fisher pelts were traded. Due to the secretive nature of fisher and the scarcity of records and accounts during the last century, it is difficult to estimate the exact timing or progression of fisher extirpation in Pennsylvania
Pennsylvania’s present day fisher population is the direct result of natural expansion from adjacent states and from reintroduction programs here. In 1969, West Virginia reintroduced 23 fisher obtained from New Hampshire. Fisher populations in West Virginia have since expanded throughout that state and into western Maryland, northern Virginia, and southwestern Pennsylvania. Similarly, New York transferred 30 fishers from the Adirondacks into the Catskills Region during 1979, and current populations in northeastern Pennsylvania may have been colonized or enhanced by natural dispersal from New York. Most recently and significantly, during 1994-1998, through a joint project between the Game Commission, the Pennsylvania State University and the Department of Conservation and Natural Resources 190 fishers (87 males, 97 females, 6 of unknown sex) were reintroduced in six sites in northern Pennsylvania.
Today, fisher populations are well established and increasing throughout southwestern, central and northern regions of the state, and fisher have become established even in some rural and suburban habitats once thought unsuitable for this adaptive forest carnivore. As fisher populations have increased, the Game Commission has adopted a scientifically based and highly conservative management plan to ensure that the fisher will remain an important forest carnivore in Pennsylvania forests.