North American River Otter

The North American river otter is a semiaquatic member of the weasel family that lives across most of Canada and along the coasts and inland waterways of the United States. A thick, water-repellent coat insulates it, and long whiskers help it detect prey in dark water. Fish are a favored food, though it also eats amphibians, freshwater clams, mussels, snails, small turtles and crayfish. It uses a burrow near the water's edge, usually with several tunnel openings, and females give birth there to litters of one to six young. Its eyesight is adapted for seeing underwater, so near-sightedness often lets it approach within a few meters of a boat or person on shore.

About the North American river otter

The North American river otter is a semiaquatic member of the weasel family, Mustelidae, found across most of Canada and much of the United States. It belongs to the otter subfamily Lutrinae and lives in rivers, lakes, marshes, estuaries and coastlines, hunting fish and crayfish with the help of long, sensitive whiskers.

Its scientific name is Lontra canadensis, and the species epithet means "of Canada." It was first described in 1777 and originally placed in the genus Lutra, the Old World river otters. Today it sits in Lontra, the genus that holds all the New World river otters. Locally it goes by many other names, including northern river otter, Canadian otter, fish otter and land otter. Other otters in the same subfamily include the Asian small-clawed otter and the giant otter of South America, from which the river otter's line split millions of years ago.

The body is long and streamlined, with short legs, fully webbed and clawed feet, and a thick, tapering tail that makes up about one-third of the total length. The head is wide and rounded, with small ears and nostrils that close underwater. Fur is dense and soft, dark brown to nearly black on top and paler underneath, with a golden-brown wash on the throat and cheeks. That thick, water-repellent coat protects and insulates the otter in cold water.

Males are larger than females. An average adult male weighs about 11.3 kg (25 lb) against about 8.3 kg (18 lb) for a female, and big males can top 15 kg (33 lb). The eyes are tuned for underwater vision, which leaves otters near-sighted on land, and a transparent inner eyelid, the nictitating membrane, shields the eyes while swimming. Like most mustelids they have 36 teeth: sharp canines and carnassials for killing prey, and large molars for crushing mollusk shells.

Behavior and diet

River otters are famously playful. Wrestling and chasing are the commonest games, and they also slide down mud and snow banks, burrow through snow and play in the water. Much of this play has a job to do: it strengthens social bonds, sharpens hunting and fighting skills and helps spread scent marks. They live alone or in family groups, usually a mother with her young, and are only loosely territorial, tending to avoid each other rather than fight.

They are mostly active at night but can be seen at any time of day. A very high metabolism means they need to eat a lot. Adults can take 1.0–1.5 kg (2.2–3.3 lb) of fish a day, and they can stay underwater for up to 8 minutes while hunting. On land they are quick too, reaching about 29 km/h (18 mph). In murky water, where sight, smell and hearing are dulled, the whiskers do the work of finding prey on the bottom.

Fish are the core of the diet year-round. One Alberta study found fish remains in 91.9% of 1,191 scat samples. Otters favor slow, easy-to-catch fish such as suckers, catfish, sunfish, carp and perch over fast game fish like trout, though they will take trout, pike and salmon when those fish are spawning. Small fish are eaten in the water, while larger catches are brought ashore. In some places crayfish matter even more than fish: in a central California marsh they made up nearly the whole diet at certain times of year.

Beyond fish and crayfish, otters eat frogs, salamanders, snakes, small turtles, molting ducks, aquatic insects and the odd small mammal such as a muskrat or vole. They have been seen ambushing hibernating adult common snapping turtles, which weigh about as much as an otter does. They are not scavengers and avoid carrion.

Otters talk with whistles, growls, chuckles and screams. They also scent-mark using paired glands near the base of the tail, which give off a strong musky smell, and by leaving urine and droppings on vegetation.

Males and females meet only to mate, in late winter or early spring, and a male may breed with several females whose ranges overlap his. The species uses delayed implantation: the fertilized egg does not attach to the uterus straight away, so although true gestation is about two months, young can be born up to a year after mating. Births run from November to May, peaking in March and April.

Females do not dig their own dens. They take over burrows made by other animals, such as beavers, and give birth to one to six pups, usually two or three. Pups are born furred but helpless, open their eyes at about one month and are weaned at around three months. Their mother introduces them to the water at about two months old. Young otters often stay with the family until the next spring and reach maturity at two to three years.

Range and habitat

Despite the name, this otter is not tied to rivers. It lives in nearly any permanent water with a steady food supply, from lakes and inland wetlands to tidal flats, estuaries and rocky sea coasts. It handles a wide range of temperatures and elevations. Dens, called holts, sit in other animals' burrows, under logs or in riverbanks, with an entrance that may open underwater and a nest chamber lined with leaves, grass, moss, bark and hair.

The species occurs across Canada and Alaska, including the Aleutian Islands, and along the Pacific Northwest, Atlantic and Gulf coasts. In Mexico it was historically found in the Rio Grande and Colorado River deltas. Pollution and urbanization have pushed it out of parts of the interior United States, and it is now rare or absent in states including Arizona, Kansas, Nebraska, New Mexico, Oklahoma and the Dakotas.

Reintroduction has reversed much of that loss. Since 1976, more than 4,000 otters have been released in 21 U.S. states. Kentucky, Colorado, Minnesota and West Virginia are among the states where returning otters have done well, and in Kentucky the species is now found in all major waterways.

North American river otter vs Eurasian otter

The two river otters look alike, and the North American species was long placed in the Eurasian otter's genus. A few features separate them.

Conservation status

The IUCN lists the North American river otter as Least Concern in its 2021 assessment, because it is not declining fast enough to qualify for a threatened category. It is also listed on Appendix II of CITES, which covers species that could become threatened unless trade is controlled.

The species has had a hard history. Trapping for fur, the draining of wetlands and pollution from coal, oil, gas, tanning and timber industries wiped otters out of large areas. A 1980 review found them locally extinct in 11 U.S. states, with major losses in nine more. Clean-water rules, better furbearer management and reintroductions have since let otters reclaim much of that ground, and all Canadian provinces except Prince Edward Island, plus 29 U.S. states, now have populations stable enough to support regulated harvests.

Threats remain. Otters are very sensitive to pollution and vanish from tainted water. Oil spills are a local danger on the coasts, and acid drainage from coal mines kills off their prey in some areas. Natural predators include bobcats, coyotes, cougars, wolves, bears, birds of prey and American alligators.