This is a mustelid, a relative of weasels and wolverines, called a fisher. The scientific name is Pekania pennanti. They’ve never been very common, and are getting less so. (A Florida fisher-relative known as “the cracker dogkiller” is basically considered a cryptid – no one is sure if it really exists.)
They’re not actually fond of fish; the name might come from a Dutch word that means “polecat.” They’re hunters and scavengers, and one of the few animals known to be able to kill a porcupine. They measure between 3 and 4 feet from snout to tail, and have a soft, glossy coat that caused them a lot of trouble — it was prized by fur trappers to the point where fishers were hunted to extinction in many areas.
The illustration is by Cal Robinson, of the US Fish and Wildlife Service, and I found it in the USFWS image library.