River Otter
The North American river otter (Lontra canadensis), also called the northern river otter, is a sleek, playful member of the weasel family that lives in the rivers, lakes, marshes and coasts of Canada and the United States. Its long, muscular body, webbed feet, thick tapered tail and dense waterproof fur make it a fast, agile swimmer that can dive to around 18 meters and stay under for up to about 4 minutes. It eats mostly fish, especially slow moving kinds, along with crayfish, frogs and crabs. River otters are famous for play: they wrestle, chase each other and slide again and again down muddy or snowy banks, and they stay active all winter, swimming under the ice. Females raise their pups alone, while males sometimes live in groups, especially along the coast. Trapping for fur and water pollution wiped the otter out of much of the central and eastern United States by the early 1900s, but cleaner water, legal protection and the release of more than 4,000 otters in 21 states brought it back. The IUCN lists it as Least Concern, with a stable population.
What is a river otter? The North American river otter
The river otter of this page is the North American river otter, also called the northern river otter, the only otter that lives in the fresh waters of Canada and the United States. Its scientific name is Lontra canadensis; older books call it Lutra canadensis, but genetic studies moved it, together with the other otters of the Americas, into the genus Lontra. In Alaska and along the Pacific Northwest coast people often call it the land otter, to tell it apart from the sea otter that lives offshore. It belongs to the weasel family, the mustelids, along with minks, martens, badgers and wolverines. Like its relatives it has a long body, short legs and scent glands near the tail, but it is built for water: the feet are webbed, the ears and nostrils close underwater, the tail is thick and muscular, and the fur has two layers, a dense underfur that traps air and longer guard hairs that shed water. On land it moves in a bounding gallop and can slide on its belly across snow and ice. Most of the time it is seen alone or in small family groups, swimming with only the head above water, often leaving a V shaped wake and a trail of bubbles.
Types of otters: how many otter species are there?
There are 13 species of otters in the world, and the North American river otter is one of four in the genus Lontra, the otters of the Americas. The others are the neotropical otter, often called the South American river otter, found from Mexico to Argentina; the southern river otter of Chile and Argentina; and the marine otter, which lives on the rocky Pacific coasts of Peru and Chile. Two more otters live in the Americas: the sea otter of the North Pacific and the giant otter of the Amazon, the longest otter on Earth at up to about 1.8 meters. In Europe, Asia and North Africa the common species is the Eurasian otter, which looks very similar to the North American river otter but has a slightly smaller, rounder head. Asia also has the smooth coated otter, the hairy nosed otter and the Asian small clawed otter, the smallest otter in the world at about 3 to 5 kilograms. Africa has the African clawless otter, the Congo clawless otter and the spotted necked otter, named for the pale spots on its throat. The Japanese river otter, a form of Eurasian otter that some scientists treated as its own species, was declared extinct by Japan in 2012.
River otter vs sea otter: how to tell them apart
River otters and sea otters can share the same coasts in Alaska, British Columbia, Washington and California, so they are often confused, but they are very different animals. The sea otter is much heavier, usually 14 to 45 kilograms against 5 to 14 for the river otter, with a short, flattened tail and a big, pale head. It spends almost its whole life in the ocean, floats on its back to eat, rest and even sleep, and uses stones to crack shellfish on its chest. The river otter is slimmer, with a long, thick tail that tapers to a point. It swims belly down, comes ashore often to eat, groom, rest and raise its pups in dens on land, and it eats mostly fish. On the coast a river otter will happily hunt in the sea, but it always needs fresh water nearby to rinse the salt from its fur. A quick way to tell them apart: if the otter is floating on its back in a kelp bed, it is almost certainly a sea otter; if it is running across the rocks, sliding down a bank or swimming with just its head out of the water, it is a river otter. Sea otters are listed as Endangered by the IUCN, while river otters are Least Concern.
How big is a river otter?
A North American river otter measures about 66 to 107 centimeters from nose to the base of the tail, plus a tail of 30 to 50 centimeters, for a total length of roughly 90 to 130 centimeters. Adults weigh 5 to 14 kilograms, and males are about 5 percent larger and noticeably heavier than females. The tail makes up about a third of the body length; it is thick and muscular at the base and works as a rudder and a powerful paddle. The feet are short and wide, with five toes joined by webbing and short claws, and the hind feet are larger than the front ones. The fur is dark brown on the back, often looking black when wet, and paler, more silvery or grayish on the throat, chin and belly. It is one of the densest furs of any land mammal, with tens of thousands of hairs per square centimeter, which is why otters spend so much time grooming: clean, fluffed fur holds the layer of air that keeps them warm in icy water. Long, stiff whiskers on the muzzle are sensitive to touch and water movement, and help the otter find fish in dark or muddy water where it cannot see well.
Where do river otters live?
The North American river otter lives across most of Canada and the United States. The IUCN lists it in every Canadian province and territory except Prince Edward Island, where it is extinct, and in nearly every US state, from Alaska and Washington to Florida, Texas and Maine; it considers it possibly extinct in New Mexico, even though otters were released on the Rio Grande there in 2008. Its presence in Mexico, where it once lived along the Rio Grande and the Colorado River delta, is uncertain today. Within that range it uses almost any clean water with enough food: rivers and streams, lakes and ponds, beaver wetlands, cypress swamps, salt marshes, estuaries and rocky sea coasts, from sea level to about 3,000 meters in the mountains. It is common along the coasts of Alaska and British Columbia, where it hunts in the sea, and in the swamps and marshes of the Southeast, from the Florida Everglades to the bayous of Louisiana and East Texas. River otters do not dig much themselves. They den in old beaver lodges, muskrat burrows, hollow logs, rock piles and tangles of roots near the water, and a single otter may use many dens along a home range that can stretch for tens of kilometers of river.
What do river otters eat?
Fish are the heart of the river otter's diet, but it is a practical hunter rather than a picky one. Studies of otter droppings, called spraints, show that it mostly catches slow, abundant fish that are easy to chase down, such as suckers, sunfish, carp, catfish and sculpins, rather than fast trout. In many places crayfish are the second most important food, and in summer they can become the main one. Frogs, salamanders, turtles, aquatic insects and the occasional bird, egg or small mammal such as a muskrat or young beaver round out the menu. On the coast, river otters eat rockfish, sculpins, crabs and other shore animals, and they will raid fish runs, catching spawning salmon in Alaska and British Columbia. An otter hunts by swimming fast underwater in short dives, chasing fish into corners or under banks and using its sensitive whiskers when the water is murky. It can swim at about 10 to 13 kilometers per hour, dive to around 18 meters and stay under for up to about 4 minutes. Small prey is eaten in the water, while bigger fish are carried to the bank or onto the ice. An adult eats roughly 1 to 1.5 kilograms of food a day, so a family needs a healthy stretch of water.
How do river otters live? Play, slides and winter
River otters are famous for play. Young otters and adults wrestle, chase each other, toss pebbles and slide again and again down muddy banks and snowy slopes, climbing back up to do it over. Sliding is also a fast way to travel, and in winter otters move across snow and ice by alternating a few bounds with long belly slides. They do not hibernate. In the coldest months they keep hunting under the ice, using breathing holes, beaver lodges and air pockets along the banks, and they can travel long distances overland between lakes and rivers. Their social life is flexible. The basic unit is a mother with her pups, which stay with her until late summer or fall. Adult males are usually more solitary, but on coasts like those of Alaska and the Pacific Northwest they may form groups of several males that fish and rest together. Otters keep in touch with chirps, whistles, chuckles, growls and screams, and they leave messages for each other at latrines, shared spots on the bank where they leave droppings and scent from glands near the tail. Most otters are active in the morning and evening, but in places with many people they become more active at night.
River otter pups and family life
River otters mate in late winter or spring, often in the water, but the embryo does not start growing right away. Thanks to delayed implantation, it floats in the uterus for many months, and real development lasts only about 60 days, so the young are born almost a year after mating, usually between February and April. This lets the pups arrive in spring, when food is easiest to find. A litter has one to six pups, also called kits, most often two or three. They are born blind, toothless and covered in fine fur, weighing around 130 grams, in a den near the water. Their eyes open at about five weeks, and they leave the den for the first time at around two months. Young otters are not natural swimmers: the mother has to coax them into the water and teach them, sometimes carrying them on her back or pulling them in. They begin eating solid food at about two to three months and learn to hunt by following her. The family stays together through summer and fall, and the young usually disperse before the next litter is born, sometimes traveling far to find a territory. Females can breed at about two years of age, while most males start a few years later.
Why are river otters a sign of clean water?
As a predator near the top of freshwater food webs, the river otter depends on everything below it. It needs plenty of fish and crayfish, clean water to see and hunt, and wooded or vegetated banks for dens and resting places, so a river with a healthy otter population is usually a river in good shape. Because otters eat so much fish, they also concentrate pollutants that build up in food chains. In the twentieth century, mercury, PCBs and pesticides were found at high levels in otters from polluted rivers, and those chemicals may have affected their health and breeding. For that reason, biologists use otters, and the droppings they leave at latrines, to check for contaminants and to track how rivers recover after cleanups. Otters also link land and water. Along the coast, latrines where otters leave the remains of fish and crabs add nutrients from the sea to the soil, and studies in Alaska found that the plants growing at these sites are greener and richer in nitrogen than those nearby. In beaver country, otters and beavers often share the same ponds, and otters may use or enlarge beaver lodges and dams as dens and travel routes.
Are river otters endangered? A conservation comeback
No. The IUCN lists the North American river otter as Least Concern, in an assessment made on 9 January 2020 and published in 2021, and it describes the population as stable. That status is the result of one of the great wildlife recoveries in North America. By the early 1900s, heavy trapping for the fur trade, water pollution and the draining of wetlands had wiped out otters from much of the central and eastern United States and from parts of Canada. Laws that regulated trapping, the US Clean Water Act of 1972 and the return of beavers and wetlands set the stage for a comeback. Then, between 1976 and the late 1990s, 21 states and the province of Alberta released more than 4,000 otters, many of them trapped in Louisiana and other strongholds. Today otters are back in almost every state, and in many places they are trapped again under regulated seasons. The species is listed on Appendix II of CITES, mainly because its pelts look like those of threatened otters. Threats remain in some areas: pollution, wetland loss, accidental drowning in fish traps and crayfish pots, and road deaths. It is extinct on Prince Edward Island, and its status in Mexico is uncertain.
Where it is found
The River Otter can be found in places such as:
