River otters belong to the family Mustelidae, which includes weasels, minks, and skunks. They are semi-aquatic, large (90-120 cm or 35-50 in) mammals with a short, blunt snout and conspicuous whiskers used to locate food in turbid water. River otters have small eyes and ears, thick necks, legs that are short and stout, and webbed toes. The tail is long and thick and tapers at the tip, and the ears and nose are protected by flaps of tissue that close when the animal is under water. Many genera in the family Mustelidae are sought for the beauty of their fur. That of river otters is dark brown, oily and very dense, with the face and breast of the animal having a grayish sheen. Both sexes are similar in appearance, with males being larger than females.
Habitat and Biology
River otters are found in Canada, Alaska, the Pacific Northwest, the Great Lakes states and along the Atlantic coast and Gulf of Mexico. River otters are adaptable animals inhabiting a variety of aquatic habitats including ponds, rivers, and saltmarshes. In South Carolina, they are common along waterways of the coastal plain.
The reproductive biology of river otters, as in other Mustelids, is unusual in that they exhibit delayed implantation. The fertilized eggs float around in the uterus for about 9 months before implantation occurs, rather than implanting on the uterine wall shortly after fertilization. Gestation lasts about 60 days, and the young, called kits, are born almost 1 year after conception. The female otter usually gives birth to two to four kits in a den located in a hollow tree or some other type of shelter. Kits are helpless and blind at birth but are fully furred. Their eyes open after about 3 weeks, and they take to the water in about 8 weeks. Female otters teach their young swimming and foraging skills until they can look after themselves, usually by 6 months. However, kits usually stay with their mother until they are 1 year old. Adult male otters do not participate in caring for the young.
River otters establish home ranges that vary in size depending on the animals age and gender and on food availability. They are most active from dusk to dawn, but diurnal activity it is not uncommon. River otters are carnivores, feeding mainly on fish, especially slow-moving species. Crayfish, where available, are also important food items. Crabs, amphibians, and other aquatic organisms are also a part of the otter's diet. River otters are very curious and playful animals. They engage in more play behavior, either by themselves or with other otters, than do most other wild animals. River otters live about 15 years in the wild.
River otters were heavily harvested for their fur throughout much of their historic range. Currently, 27 states and 11 Canadian provinces have otter trapping seasons. However, otter harvest in North America is no longer considered to be a threat to the species. In South Carolina, the average number of otters harvested commercially over the past 20 years was 478.
Otter fur harvest, which peaked in the northern United States around 1800, was the main factor contributing to the decline of the species throughout North America. Currently populations of river otters are threatened by pollution (including pesticide poisoning), acid rain, habitat loss, and illegal hunting. The river otter is not an endangered species in South Carolina, but it is listed as such in other states where it occurs.
Foster-Turley, P., S.M. MacDonald, and C.F. Mason (eds.). 1990. Otters: An action plan for their conservation. International Union for Conservation of Nature and Natural Resources, Gland, Switzerland.
Golley, F.B. 1966. South Carolina mammals. Charleston Museum, Charleston, SC.
Webster, W.D., J.F. Parnell, and W.C. Biggs. 1985. Mammals of the Carolinas, Virginia, and Maryland. University of North Carolina Press, Chapel Hill, NC.