Physical Description

The river otter has a long, streamlined body, short legs, and a robust, tapered tail. The whiskers are prominent and located just behind and below the nose. The neck and shoulders are thick and muscular. Feet are webbed between the toes. The short, thick, soft fur is brown to almost black except on the chin, throat, cheeks, chest, and belly, where usually it is lighter. Adult male otters reach an average length of 45 inches and weight of 25 pounds, but may reach 31 pounds. Sex is distinguished by the presence of a baculum (penile bone). Females have four mammae on the upper chest and are slightly smaller than males. Females measure about 36 inches and weigh 19 pounds. The average weights and sizes of river otters in southern latitudes tend to be lower than those in the north.