Field Guide/Mammals/Fisher

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Martes pennanti (Fisher)
Family: Weasel
Size: The male Fisher is larger than the female Fisher.

Total Length: 29.5-47.2 inches (75-120 cm)

Weight: 4.4-12 pounds (2.0-5.5 kg) [1]
Description: The Fisher is a medium sized mammal whose body type resembles a weasel. This mammal is long, thin, and short to the ground. The dark brown to black fur changes among seasons and varies by gender. The tail is long and bushy. The Fisher has a muzzle similar to a dog.[1]
Similar Species: Fishers are larger in size and darker in color compared to similar species such as the American Marten (Martes americana. In addition, many similar species may have a cream colored patch near their chin or chest, but the Fisher does not have this marking.[1]

Range: Fishers are native to North America and can only be found here. They are often found in the northern parts of North America, but may live in the Appalachian and Pacific Coast Mountains.[1]
Habitat: Fisher live in forests such as dense lowlands and spruce forests. They find areas that have a continuous canopy and avoid forests with open areas.[2]
Diet: Fishers are omnivores that have a diverse diet. They often eat birds, reptiles, and insects as well as carrion, berries, and nuts. Fishers kill other animals to eat such as squirrels, deer fawns, mice, chipmunks, porcupines, and snowshoe hares.[3]
Activity: The Fisher is diurnal, or can be found active during the day and the night. Their activity levels vary throughout the year. Males are more active during their breeding season while females are less active because they care for the young.[4]

Reproduction: Fishers experience delayed implantation where the female is impregnated shortly after giving birth. The delayed implantation lasts 10-11 months. Breeding and births occur in the spring usually from March to May. Fishers usually give birth to three babies, but may give birth to up to six at a time. Females are sexually mature at one year old, but they give birth for the first time around two years old. Males become sexually mature between one and two years old.[1]
Lifespan: In both captivity and in the wild, Fisher usually live to be ten years old. In zoos, some Fishers have lived to be older than ten years old. This species does not have a lot of predators, so they usually live until old age.[1]

Notes: Fishers were nearly extinct in Minnesota in the 1900s, but their population has increased and is now stable. They are listed under least concern on the IUCN Red List. Fishers are more often predators of other animals than they are the subject of predation. They may compete against bobcats, coyotes, and large raptors while gathering prey. They are one of few animals that kill porcupines. Female Fishers are pregnant 350 days out of the year due to their delayed implantation reproductive methods. Fishers are solitary animals with the exception of mother raising young and mating.

  1. a b c d e f Powell, R (1981), "Martes pennanti", Mammalian Species 156: 1–6,, retrieved (October 4, 2012) 
  2. Minnesota Department of Natural Resources (2012), Fisher,, retrieved October 4, 2012 
  3. Ziel, W; Duncan, N (2004), "Diets of Sympatric Populations of American Martens (Martes Americana) and Fishers(Martes Pennanti) in California", Journal of Mammalogy 85 (3): 470–477 
  4. Weir, R; Corbould, F (2007), "Factors Affecting Diurnal Activity of Fishers in North Central British Columbia", Journal of Mammalogy 88 (6): 1508–1514