Fishers, a small member of the weasel family, were once common in the old-growth forests of the St. Croix Valley. But today, they are making a comeback, according to Joe Winter, writing in the Stillwater Gazette:
The fishers traverse river valleys, such as the St. Croix, and their trees need to be taller than 60 feet and have many horizontal limbs so they can move about, said Harvey Halvorsen, wildlife biologist for the Wisconsin Department of Natural Resources in the Baldwin office, which covers all of St. Croix County. That means aspen won’t cut it for habitat, and fishers more typically require trees such as maple, pine or oak. The latter often grow in the blufflands of the St. Croix, but their branches are usually shorter and run more vertically.
Fishers are capable of crossing frozen rivers to get to the Stillwater area, then live in the bluffline trees of the more diverse Minnesota side, and even somewhat more heavily populated suburbs are not seen as a problem for them, as long as the right trees are around, Halvorsen said.
Despite the growth in population in western St. Croix County, the number of fishers has steadily increased there for each of the last 10 years, Halvorsen said. The new Stillwater bridge and the population and business growth it could bring may change that pattern because habitat almost certainly will be reduced.
The return of fishers has primarily been noted by local fur trappers. Both Minnesota and Wisconsin have trapping seasons for the animals.
According to the Minnesota Department of Natural Resources, fishers cover a range of seven to 10 square miles. They are carnivorous, and are one of the few animals that can kill a porcupine. They also eat snowshoe hares, mice, squirrels, and insects and berries. They have also been known to kill domestic cats.