Chapter 3 Fisher

The fisher (Martes pennanti) is a medium-size mammalian carnivore and the largest member of the genus Martes (Anderson 1970) of the family Mustelidae in the order Carnivora. The genus Martes includes five or six other extant species. The fisher has the general body build of a stocky weasel and is long, thin, and set low to the ground. A fisher's head is triangular with a pronounced muzzle, its ears are large but rounded, and its eyes face largely forward (Douglas and Strickland 1987). Adult male fishers generally weigh between 3.5 and 5.5 kg and are between 90 and 120 cm long. Adult female fishers weigh between 2.0 and 2.5 kg and are between 75 and 95 cm long. The weights of adult females are more constant than those of adult males over the species' range (Powell 1993). From a distance fishers often look uniformly black but they are actually dark brown over much of their bodies. Guard hairs on a fisher's tail, rump, and legs are glossy black while those on the face, neck, and shoulders are brown with hoary gold or silver tips (Coulter 1966). The undersurface of a fisher is uniformly brown, except for white or cream patches on the chest and around the genitals. These patches might be used to identify individuals (Frost and Krohn, unpubl. data; Powell, unpubl. data). The fur of fishers is very soft and glossy but varies among individuals, sexes, and seasons. Males have coarser coats than females. The single yearly molt may begin during late summer and is finished by November or December (Coulter 1966; Grinnell et al. 1937; Powell 1985, 1993). During September and October, the guard hairs are noticeably shorter than during the rest of the year, giving fishers a sleek appearance. Fishers have five toes on all four feet. Their claws are retractable but not sheathed. Fishers are plantigrade and their feet are large. There are pads on each toe and four central pads, one each behind digits 1, 2 and 3, 4, and 5, on each foot. From the central pads to the heels of the hindpaws, there are coarse hairs covering tough skin. The small, circular patches of coarse hair on the central pads of the hindpaws are associated with plantar glands and carry an odor distinctly different from other fisher odors (Buskirk at al. 1986; Powell 1977, 1981a, 1993). Because these patches enlarge on both males and females during the breeding season (Frost and Krohn, unpubl. data), as they do in American martens (Martes americana; Buskirk et al. 1986), they are probably involved in communication for reproduction. Fishers leave a characteristic mustelid track pattern: two footprints next to each other but slightly out of line. Deep, fluffy snow and thin crusts restrict fishers' movements (Grinnell et al. 1937; Heinemeyer 1993; Leonard 1980b, 1986; Powell 1977; Raine 1983) and, to avoid deep snow, fishers sometimes hunt in habitats in which they can travel most easily rather than in habitats that have most prey (Leonard 1980b; Raine 1983, 1987). Distribution of deep winter snow may limit fisher distribution (Aubry and Houston 1992; Krohn et al., in press) and may affect success of reintroductions (Heinemeyer 1993) and perhaps reproduction (Krohn et al., in press). At the time of European settlement, fishers were found throughout the northern forests of North America and south along the Appalachian and Pacific Coast mountains (Graham and Graham 1994). The northern limit to the range is approximately 60°N