Home ranges may approach 30 square miles for males and about 12 square miles for females. Female fishers are sexually mature when one year old, while males don't normally achieve sexual maturity until their second year. Breeding occurs in the spring and the overall gestation period lasts almost a year. Fishers have relatively low reproductive rates, producing one litter a year that averages around two or three cubs, which are born and raised in a tree cavity. Young fishers develop rapidly and are weaned at five to eight weeks, but do not disperse from the natal area and venture out on their own until about six months of age.
Fishers are solitary, opportunistic predators.
In fact, fishers seldom if ever hunt for fish. When hunting, fishers do not seek out a specific prey item. Instead, they select prey based on abundance and catching ease. Consequently, the diet varies considerably by geographic region. In most parts of the fisher's range, mice, shrews, squirrels, chipmunks and porcupines are important prey items.