River otters (Lontra canadensis, Figure 1) are members of the weasel family, best known for their playful behavior, aesthetics, and value of their durable, high-quality fur.
The loss of ponds and other wetland habitat that resulted from the extirpation of beaver in the late 1800s may have adversely affected continental populations of river otters more than any other factor. Increases in the range and number of river otters in response to the return of beaver has been dramatic, particularly in the southeastern US. Releases totaling more than 1,000 otters have been made in Arizona, Colorado, Iowa, Kansas, Kentucky, Missouri, Nebraska, Oklahoma, Pennsylvania, Tennessee, and West Virginia in efforts to reestablish local populations.
River otters are listed in Appendix II of the Convention on International Trade in Endangered Species of Flora and Fauna (CITES). The inclusion in this appendix subjects river otters to international restrictions and state and province export quotas because of their resemblance to European otters. River otters are protected from trapping, hunting, and other harvest in 17 states. Twenty-seven states have seasons for trapping, and four states and two provinces have seasons for hunting.
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.
River otters occur throughout North America except the arctic slopes, arid portions of the Southwest, and intensive agricultural and industrialized areas of the Midwest.
Populations of otters are confined to water courses, lakes, and wetlands, and therefore, population densities are lower than those of terrestrial species. Extirpation of otters from many areas is believed to be related to poisoning by pesticides that are bio-magnified in fish, their main source of food.
Voice and Sounds
Vocalizations include a snarling growl or hissing bark when disturbed, low grunts when playing or traveling, and a loud snort through the nose when alarmed. Low-frequency chuckles are uttered when otters are in groups.
Tracks and Signs
Otters habitually use specific sites (latrines) for defecation (Figure 3). Otters usually eat small catfish whole, except for the head and spine. Small trout, salmon, and many of the scaled fishes may be eaten whole. Carcasses that have large puncture holes suggest predation by a heron rather than an otter.