The “Fisher”– Obscure, Reclusive North American Mammal You Have Never Seen

Fisher CatIII First of all, what are Fishers? Most people have never heard of them. Fishers (Martes pennanti) are a small carnivorous mammal found native to North American forests of northern U.S. and Canada.* Biologists generally agree that all North American fishers belong to the same species; they are considered monotypic–there are no subspecies. They belong to the Mustelidae, the weasel family and are most closely related to the American marten, only larger–similar in size to domestic cats. They may reach 15 pounds in weight with length of nearly 4 feet. Fishers dwell in forests of Canada and the northern United States. Although it is sometimes called a “cat,” it is not closely related to felines although both are classified as carnivores.

Male fishers are much larger than females, although similar in appearance. Bodies are set low to the ground. They have distinctive scent glands. Fishers are able to turn their hind feet almost 180 degrees, which allows them to descend trees head first. Their fur changes with the seasons. When winter approaches their brown to black fur becomes dense and glossy. Belly hair is usually brown with occasional patches of cream colored hair. During late summer molting cycle, fur becomes more variable and often becomes lighter, even mottled.

Fishers prefer to hunt prey in a full forest with canopy (overstory) and usually avoid humans. They are solitary hunters and are omnivores. They seek food around fallen trees eating berries/fruits, mushrooms and insects, in addition to small mammals and birds, especially snowshoe hares and porcupines. They are the only known predators of porcupines, which they attack by biting the porcupine’s head multiple times, killing them in 20 to 30 minutes. There is evidence of carrion feeding—on dead carcasses of moose and deer. Even larger animals such as wild turkey, bobcat and lynx are sometimes known to have been preyed upon. Fishers have few enemies aside from humans.

Fishers usually den in hollow trees. Three or four blind and helpless (altricial) “kits” are born in the spring, covered with very fine hair. Their eyes open at about 7 weeks and they begin to climb at 8 weeks during which time they are dependent upon mother’s milk, soon changing to a more solid diet. Adult females care for their young for about 5 months when they are pushed out of the den to become self sufficient on their own.

The female parent goes into estrus soon after giving birth and leaves the den to find a mate. The fisher reproductive cycle lasts about a year. Fishers have delayed implantation, that is, the resulting fertilized egg becomes a blastocyst (pre-embryo) and doesn’t implant on the uterine wall of the female until the following spring. Males reach reproductive maturity at one or two years of age while females are reproductively active at one year, giving birth to their first litters at age two.

Fishers were trapped for their fur in the 18th and 19th centuries. Their pelts were in such high demand that intensive trapping resulted in their being exterminated from some of their U. S. habitat in the early 1900s. In the 1920s, when pelt prices were high, fur farmers attempted to raise fishers domestically. However, delayed implantation typical of fishers, made breeding quite difficult and most fur farming ceased when pelts dropped in value in the 1940’s.

Fishers are most active in early morning and late afternoon hours (crepuscular) year around, although they have been observed to be active during the day and nighttime also.  They are loners, only associating with others for mating purposes. The size of a fishers hunting range is from 3 square miles in summers to 5 square miles in the winters, though it may be much larger if habitat food is scarce. Male and female territories are overlapping.

Internal parasites are cestodes and nematodes. In captivity (zoos), fishers have lived more than 10 years. Fishers may vocalize with a low chuckle (excitement), a hiss and a growl, the latter two associated with aggression.

A recent newspaper article** discussed the possibility of Northern Rockies Fishers (Martes pennanti) being designated as an Endangered Species. Due to trapping, poisoning and habitat loss, a year long study will be undertaken by the U. S. Fish and Wildlife Service.  In the past, fishers have occupied northern Rocky Mountain ranges in Washington, Utah, Idaho, Montana and Wyoming, though at present they are thought to be found only along the Idaho-Montana border. Only Montana presently allows trappers to harvest fishers—up to 7 annually.

*Powell, Roger A. 1981. Martes pennanti.   Mammalian Species, No. 156. American Society of Mammalogists publication.

**Matthew Brown, Associated Press, 13 Jan 2016. Feds consider protections for cat-like predator. Deseret News, Salt Lake City, UT

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