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. In northern areas such as Wisconsin and Minnesota, fishers often prey on snowshoe hares and grouse.
Food acquired by scavenging also constitutes a significant portion of the fisher's diet.
For example, in many areas, gut piles and deer carcasses provide fishers with an abundant late-fall and winter source of food. When available, apples, nuts and other fruits are readily eaten by fishers. Because of their varied diet and low densities, fishers do not appear to affect most prey populations. Fishers are among the few animals that regularly prey on porcupines, though, and are known to control porcupine populations. In fact, some states have reintroduced fishers for the purpose of reducing porcupine numbers.