River Otters

This tool lists various Habitat Fact Sheets developed by the Region 5 Regional Response Team. To suggest additions to this tool, please contact Barbi Lee. Click here for Inland Response Tactics Manual and  Submerged Oil Recovery Tactics.

I. Habitat Description

North American river otters are semi-aquatic mammals, with long, streamlined bodies, thick tapered tails, and short legs. They have wide, rounded heads, small ears, and nostrils that can be closed underwater. The whiskers are long and thick. The fur is dark brown to almost black above and a lighter color on the underside. The throat and cheeks are golden brown. The fur is dense and soft, effectively insulating these animals in water. The feet have claws and are completely webbed. Body length ranges from 35 to 51 inches and tail length from 12 to 20 inches. Weight ranges from 11 to 30 lbs. Males average larger than females in all measurements.

River otters are found in Canada, Alaska, the Pacific Northwest, the Great Lakes states and along the Atlantic coast and Gulf of Mexico. Vegetation adjacent to rivers, streams, lakes, and other wetland areas are key habitats. Adult males live along large stretches of river, often up to 40 to 50 miles. Females are not as mobile. Their home ranges are only 3 to 10 miles depending on habitat quality and the time of year. They travel a lot but spend most of their time at activity centers with abundant food and cover. Examples of these centers include logjams, oxbows, pools below dams or spillways, and springs or riffles that stay free of ice all winter.

River otters eat mainly aquatic organisms such as amphibians, fish, turtles, crayfish, crabs, and other invertebrates. Birds, their eggs, small terrestrial mammals, and sometimes aquatic plants are also eaten on occasion. Prey is eaten immediately after capture, usually in the water, although larger prey is eaten on land.

II. Sensitivity to Oil Spills

River otters spend a great deal of time swimming and diving in for food. Their fur can become oiled while in the water, resulting in a loss of insulation and hypothermia. In addition, river otters groom frequently and can ingest oil as a result. While they prefer live prey, they are also opportunistic feeders and potentially will eat oiled carrion, especially during the winter and spring. Ingestion of hydrocarbons during the grooming process or through feeding on contaminated prey items may result in digestive-tract irritation, neurological effects and physiological changes, which in turn, may lead to organ injury, dysfunction, and death. Aromatic hydrocarbons are capable of causing inhalation injury and may cause death before either hypothermia or ingestion injuries affect the animals.

III. Sensitivity to Response Methods

The following text describes potential adverse impacts to river otters resulting from various oil spill response methods and/or provides recommendations to reduce impact when these methods are implemented. This is not intended to preclude the use of any particular methods, but rather to aid responders in balancing the need to remove oil with the possible adverse effects of removal with respect to river otters. More detail about the response methods themselves can be found in the Inland Response Tactics Manual.

Additional Information