The Fisher is a medium size member of the mustelid family often compared to the American Marten, a slightly smaller mustelid, due to many shared habits and characteristics. The “fisher-cat” is neither much of a fish catcher nor is it a member of the cat family though it does resemble a house cat in general body size and shape, but the fisher has shorter legs and a longer, wedge- shaped snout. The fur on a fisher is dark brown to black, as an animal ages the hair tips may become ‘frosted’, especially around the head and shoulders. They molt in the fall. Males generally have coarser hair coats, this makes the females more desirable to trappers. Their bodies measure 20 – 30 inches with an additional 13 – 17 inches of tail and weigh from 3 – 12 pounds. Males are usually significantly larger than the females. Tracks reveal 5 toes in a plantigrade foot averaging 3 in. wide by 4.5 in. long with thick fur on the soles of their feet in winter. The nails are at least partially retractable though not sheathed and the mustelid, 2×2 bounding gate is most common with fisher track patterns. (see tracking section for illustrations)
Fishers are considered to be quite carnivorous, favoring snowshoe hares as well as squirrels, carrion, mice, shrews, voles, birds, fruits like berries, and ferns. They are also famous for their ability to successfully hunt and kill porcupines. One of the very few other animals to prey on porcupines is a close cousin of the fisher, the wolverine. The fishers’ long, wedge-shaped snout is well suited for making vicious attacks to the porcupines face until mortal wounds cause the porcupine to succumb. In some forests, fishers have been reintroduced to try to control porcupine populations. This biological control method has been successful at least for short-term population reductions; it is currently unknown how well it works for long-term porcupine population control. They generally hunt by systematically searching for patches of abundant prey and then systematically searching those patches for prey to kill. Fishers will sometimes cache food items and find/make temporary den sites near large food items like a deer carcass.
The breeding season for fishers is in late March and April. Like most other mustelids, fishers experience delayed implantation of 10 – 11 months. The egg is fertilized at the time of mating, then the embryo stops developing and remains in a dormant state until the female is in good physical condition during late winter, the embryo then implants and develops. The actual gestation lasts approximately 30 days with parturition (birth) occurring in March and April. They typically breed again within 10 days of parturition. Females breed at one year and have their first litter of about 3 kits at age 2 years. Males are probably not sexually mature until age 2. Fishers are pretty solitary animals except during the breeding season when plantar glands on their hind feet increase secretions and a black, tarry substance of unknown origin signal their intent to mate.
Fisher natal and maternal dens are usually located high (+/- 50 ft.) in tree cavities which partially explains their overall preference for mature to old growth, late successional, forest habitats. Researchers have noted significant use of young to mature forests during the winter. They also require significant tracts of contiguous forest with a high degree (70%) of canopy cover and prefer conifer or mixed conifer and northern hardwood forest types. They are also disproportionately associated with riparian communities for less than well known reasons. Fisher distribution and survivability is negatively impacted by forest fragmentation, stand isolation, and deep, fluffy snow. In comparison, martens have very similar habitat requirements but they are much less inhibited by deep snow. This may be an important way in which these two species are segregated. There is a considerable span of home range size estimates from 1.5 to 25 sq. miles, probably averaging around 10 sq. miles. Once again, males tend to have much larger territories than females, which often overlap territories of more than one female but rarely that of another male. Fishers will commonly travel 2-3 miles each day and while they are arboreal to some degree, most hunting and traveling is on the ground. They mark their territories and communicate with urine and anal, cheek, abdominal, neck, flank, and plantar (feet) glands. Martes pennanti was formerly widely distributed across northern forests of N. America up to around 60 degrees N. latitude, south in the Appalachian Mountains to North Carolina, and throughout the Pacific Coast mountains. Current distribution is now well known but they have not returned to the southern Appalachians, and are considered spotty in the Pacific Coast mountains, especially in Washington and Oregon, and in the southern reaches of their former distribution in the Rockies. These medium size weasels are particularly susceptible to logging and trapping.