Illustration by Uko Gorter
River otters are related to badgers, weasels and skunks. They are not considered marine mammals and are adapted to living on land and water. They are nimble runners, and their streamlined bodies, long pointed tails and webbed toes make them fast swimmers as well.
River otters are a common site along shorelines, especially at dawn and dusk, and are found in fresh and salt water throughout the Pacific Northwest. All sites along The Whale Trail are great places to view these energetic and playful animals.
In coastal habitats, river otters are found in estuaries, marshes and the lower parts of streams. Inland, river otters are found in lowland marshes and swamps, streams and small lakes. Their dens are found in shrubbery along river banks, or in abandoned beaver, badger, fox or rabbit dwellings, and sometimes in the crawl spaces of human homes.
- River otters along the Pacific Northwest coast are equally at home in marine and fresh waters. Since they spend so much time in salt water, there is some speculation that they are evolving into a new species.
River otters become sexually mature at two years old. Mating occurs in the spring but river otters delay implantation of the embryo until the following winter. The river otter’s gestation period is only 60-63 days, and one to four cubs are born in the spring.
River otters are omnivorous and primarily eat fish, but also survive on a variety of animals including crustaceans (crayfish, crabs), mussels, insects, reptiles and amphibians, birds, and even rodents and young beaver.
- Unlike sea otters, river otters swim on their bellies and can move at speeds of up to seven miles per hour.
- They feed during the day or at night and are most active at dawn and dusk.
- They sometimes dive to depths of 50-75 ft, and remain underwater for up to five minutes hunting for food.
- River otters vocalize, using an assortment of chirps, “chuckles” and growls.
- They need to frequently groom their fur to distribute oils which maintain water resistance. You may see river otters “squee-geeing” water off their bodies against a hard surface on land.
- They are generally solitary but may spend time in family groups, usually consisting of a mother and her pups. The females drive off the aggressive males while the cubs are young. Males occasionally take part in rearing the young.
Since river otters are not considered marine mammals they are not afforded protection under the Marine Mammal Protection Act. River otters were once over-hunted in North America for their fur, and trapping still continues in Eastern Washington and British Columbia.
Urban development impacts their habitat and prey availability. Oil spills, toxins in their food supply and fishing gear entanglement are also of concern.
River Otter at Autumn Lane (Smithsonian's Backyard) by Laura Gates Galvin and Christopher Leeper, 2002
Project Otter (Zoo Life series) by Susan Ring, Diana Marshall, and Heather Kissock, 2003
Otters: Ecology, Behaviour and Conservation (Oxford Biology) by H. Kruuk, 2006
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Adult ♂ :
3 to 4 ft (1-1.2 m)
Adult ♀ :
3 ft (1 m)
Birth Length :7 to 8 inches (17-20 cm)
Adult ♂ :
20-30 lbs (9 – 13.6 kg)
Adult ♀ :
12 to 18 lbs (5.4 – 8 kg)
Birth Weight :
4 to 5 oz