The Pacific fisher is a member of the weasel family. The fishers have long, thin bodies that measure 31-40 inches in length. Their fur is mostly dark brown. Individuals weigh between three and 18 pounds, with the male being larger than the female. They den in hollow trees and rocky crevices.
Fishers are mostly nocturnal.
The prey upon porcupine and snowshoe hare, although they do eat smaller mammals, fruit, and other plants. The fisher's stomach can soften porcupine quills enough for them to pass through the animal's intestinal tract. Fishers can rotate their hind feet almost 180 degrees for running down tree trunks. Apparently, they're fast enough to run down and kill martens. Cascade Olympic Natural History .