Fishers are among the worst of all predators. They are overgrown weasels with the temperament of the wolverine. The Wisconsin DNR released them here in northern Wisconsin some years ago. I seems that the lumber companies were whining because porcupines were killing the poplar trees used by the paper mills. Never mind that one lumberjack destroys more such trees in one day than a porcupine and all its great, greats, can destroy in their lives. Fishers are about the only animals that will take on a porky and kill it. So to appease the lumber/paper industry, they released a bunch of them here. They have no natural predators here and they spread like wildfire. They did their job and all but wiped out the porkies, then started on dogs, cats, and almost decimated our small game.
Yes, they are protected here, too. If you are caught killing one you are in deep doggie doo. However, many residents kill them on sight and as far as I am considered good riddance. Of all the predators discussed on BYC, the fisher is to be the most feared. It is a raccoon on steroids, just a smart, far more brazen, far faster, and the most deadly creature you can possibly have around your chickens, pets, or anything else that it considers to be of "edible size." If you truly have a fisher hanging around, your chickens are in serious peril.