The North American river otter (Lontra canadensis), also called the northern river otter, is a mammal that lives partly in water and partly on land. It is found only in North America, across most of Canada and along the coasts and inland waterways of the United States. An adult North American river otter weighs between 5 and 14 kilograms (11–31 pounds). Its thick, water-repellent fur helps keep it warm and dry.

This otter is part of the weasel family and is equally comfortable in water and on land. It builds a den near the edge of water in places like rivers, lakes, swamps, coastal areas, tidal flats, or estuaries. The den often has multiple openings, with one leading to the water. Female otters give birth in these dens, usually having 1 to 6 young.

North American river otters eat the animals that are easiest to find. Fish, such as perch, suckers, and catfish, are their favorite food, but they also eat amphibians (like salamanders and frogs), freshwater clams, mussels, snails, small turtles, and crayfish. Occasionally, they may eat small animals such as mice, squirrels, birds, or even dogs that they have attacked and drowned.

The range of the North American river otter has decreased a lot because of habitat loss, which began when Europeans settled in the Americas. In some areas, their population is managed so people can trap them for their fur. These otters are very sensitive to pollution, which likely contributes to their declining numbers. To help protect them, several reintroduction programs have been started to increase their population.

Taxonomy and evolution

The North American river otter was first described by German naturalist Johann Christian Daniel von Schreber in 1777. This animal is known by many names, such as North American river otter, northern river otter, common otter, and simply river otter. Other names include American otter, Canada otter, Canadian otter, fish otter, land otter, nearctic river otter, and Prince of Wales otter. The species was originally placed in the genus Lutra, a name used by early European scientists. The specific name canadensis means "of Canada."

In a newer classification, the species is now called Lontra canadensis. The genus Lontra includes all river otters found in the Americas.

Scientists used molecular biological techniques to study when the river otter and the giant otter (Pteronura brasiliensis) from South America separated. These studies suggest they split apart during the Miocene epoch, which lasted from 23.03 to 5.33 million years ago. This happened much earlier than shown by fossil records. Fossils of giant otters from 3.5 million years ago have been found in the U.S. Midwest. However, fossils of the modern river otter first appeared in North America about 1.9 million years ago. The New World river otters came from Old World river otters after migrating across the Bering Land Bridge, which connected Asia and North America between 1.8 million and 10,000 years ago. Later, the otters moved southward across the Panamanian Land Bridge, which formed 3 million years ago.

Listed alphabetically:

• L. c. canadensis (Schreber, 1777) – (eastern Canada, U.S., Newfoundland)
• L. c. kodiacensis (Goldman, 1935) – (Kodiak Island, Alaska)
• L. c. lataxina (Cuvier, 1823) – (U.S.)
• L. c. mira (Goldman, 1935) – (Alaska, British Columbia)
• L. c. pacifica (J. A. Allen, 1898) – (Alaska, Canada, northern U.S., south to central California, northern Nevada, and northeastern Utah)
• L. c. periclyzomae (Elliot, 1905) – (Queen Charlotte Islands, British Columbia)
• L. c. sonora (Rhoads, 1898) – (U.S., Mexico)

Description

The North American river otter has long, thin whiskers that help it find food in dark water. An average adult male weighs about 11.3 kilograms (25 pounds), while an average female weighs about 8.3 kilograms (18 pounds). The otter's body length is between 66 and 107 centimeters (26–42 inches). About one-third of the otter's total length is its long, narrow tail, which measures between 30 and 50 centimeters (12–20 inches). Some large males can weigh more than 15 kilograms (33 pounds). This otter is different from the Eurasian otter because it has a longer neck, a narrower face, a smaller space between its ears, and a shorter tail.

Male and female river otters have different physical traits that are not related to reproduction, with males generally being larger.

North American river otters can live 21–25 years in captivity or 8–13 years in the wild.

These otters often swim close to boats or people on the shore because they have poor eyesight above water, which is adapted for seeing underwater. They have a clear inner eyelid, called a nictitating membrane, that protects their eyes while swimming.

Like other mustelids, river otters have 36 special teeth, including sharp canines and carnassials that can kill prey. They also have large molars for crushing hard objects, such as the shells of mollusks. Some otters may have extra premolars. The dental formula is 3.1.4.1 3.1.3.2.

Distribution and habitat

The North American river otter lives in many places across North America. It can be found in rivers, lakes, and coastal areas in Canada, the Pacific Northwest, the Atlantic states, and the Gulf of Mexico states. These otters also live in forested areas near the Pacific coast. They are present in all parts of Alaska, including the Aleutian Islands and the north slope of the Brooks Range.

Urban areas and pollution have caused the otters’ range to shrink in the United States. Today, they are missing or very rare in Arizona, Kansas, Nebraska, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, and Tennessee. Reintroduction projects have helped otters return to some areas, such as West Virginia and the Midwestern United States. In Kentucky, otters were reintroduced in the early 1990s and have since grown in number enough to allow a trapping season starting in 2006. Now, they live in all of Kentucky’s major waterways. In 2010, Colorado officials reported that otters reintroduced in the 1980s were doing well and suggested their protection status should be reviewed. In late 2012, a river otter named Sutro Sam was spotted near the old Sutro Baths in San Francisco, the first sighting there since the 1950s. Otters live in all Canadian provinces and territories except Prince Edward Island, where they have recently started returning. In Minnesota, otter numbers have increased because of reintroduction efforts, better water quality, habitat restoration, and rules about hunting. While otters are most common in northern Minnesota, they can also be seen in cities like the Twin Cities.

Before European settlers arrived, North American river otters were common in most major rivers and lakes in the United States and Canada. Large otter populations lived in areas with many types of water habitats, such as coastal marshes, the Great Lakes region, and glaciated areas of New England. Smaller otter groups lived in inland rivers and lakes. These otters lived along the entire Pacific Coast, including the ocean and inland streams and lakes. In Mexico, they lived near the Rio Grande and Colorado River Deltas.

Even though they are called “river otters,” these animals live in many types of water areas, both fresh and saltwater, such as lakes, rivers, wetlands, marshes, and coastal areas. They can survive in a wide range of temperatures and elevations. Otters depend on permanent water sources for food and shelter. They need steady food supplies and easy access to water, but they avoid polluted areas.

Like other otters, North American river otters live in dens. These dens are often in the burrows of other animals or in natural spaces like under logs or in riverbanks. A hole, which may be underwater or above ground, leads to a nesting area lined with leaves, grass, moss, bark, and hair.

Behavior

North American river otters live in areas with plants, rock piles, and enough cover. They are known for their playful behavior. Otters often play by wrestling with other otters and chasing each other. This play helps them learn skills needed for survival, such as fighting and hunting.

North American river otters are active predators that hunt in water. They eat fish, crustaceans, and other animals that live in or near water. The types and amounts of prey they eat depend on how easy it is to find the prey, the prey’s ability to move, the availability of habitats for prey, and environmental conditions like water depth and temperature. These factors also change with the seasons.

Scientists study the diet of North American river otters by examining their feces or the food found in their stomachs after they are trapped. Fish are the main part of their diet all year. Studies in Alberta, Canada, found fish remains in 91.9% of 1,191 fecal samples collected during each season. In western Oregon, fish remains were found in 80% of 103 stomachs examined. Crustaceans, such as crayfish, are the second most important prey in areas where they are available. In some places, like a marsh in central California, crayfish made up nearly 100% of the otters’ diet at certain times. Otters also eat fruits, aquatic plants, reptiles, amphibians, birds (especially flightless ducks during moulting), insects, small mammals, and mollusks. They do not eat dead animals or large prey, but they have been seen killing adult snapping turtles during hibernation. Otters may also eat beaver, though studies rarely show this as a regular part of their diet.

If otters are not controlled, they can harm fish populations in places like fish hatcheries or small ponds where fish cannot escape easily. To protect fish, otters may need to be moved. Even in larger water bodies, otters may target fish that are concentrated in limited areas, such as during spawning or overwintering. Cold water can slow fish, making them easier to catch. Before reintroducing otters to a region, care must be taken to protect threatened or endangered fish species.

A North American river otter’s territory can be as large as 78 km (30 sq mi), but most territories are between 8 and 39 km (3–15 sq mi). This size may change during mating seasons.

North American river otters are social but can live alone. Their bodies help them avoid predators by diving, burrowing, and twisting to escape. They play together, which strengthens social bonds, improves hunting skills, and marks territory. Otters are not aggressively territorial but often mark areas with scent to show their presence.

North American river otters differ from Eurasian otters because they use delayed implantation, a process that does not occur in Eurasian otters.

In early spring, female otters search for a den to give birth. They do not dig their own dens but use existing ones built by other animals, such as beavers. Mothers give birth to one to five kits, usually two to three. Each pup weighs about five ounces.

Female otters raise their young alone. When pups are about two months old and their fur grows in, their mother teaches them to swim. By eight weeks old, pups may leave the den and can survive on their own by autumn. They often stay with their family, which may include the father, until the next spring. When a new litter is born, older pups leave to find their own territories.

Ecology

The diet of North American river otters includes many types of food, such as fish, frogs, crayfish, turtles, insects, and small mammals. They hunt alone or with another otter and can catch prey on land or in water. Lontra canadensis is a predator that hunts in water and eats animals that live in or near water. The types of prey they eat and how much they eat depend on how easy the prey is to find and how available the prey is during different times of the year.

North American river otters eat many kinds of fish that range in size from 2 to 50 cm (0.79–19.69 in). They usually eat fish that are easy to catch and are plentiful. Slow-moving fish, like suckers (Catostomidae), catfish, sunfish, bass (Centrarchidae), daces, carp, and shiners (Cyprinidae), are eaten more often than fast-moving fish when both are available. In Colorado’s Upper Colorado River Basin, suckers (Catostomidae) are a main part of their diet. In other parts of Colorado, common carp (Cyprinus carpio) is often eaten. Fish that are frequently found in their diets include:
– Catostomidae, such as suckers (Catostomus spp.) and redhorses (Moxostoma spp.);
– Cyprinidae, such as carp (Cyprinus spp.), chubs (Semotilus spp.), daces (Rhinichthys spp.), shiners (Notropis and Richardsonius spp.), and squawfishes (Ptychocheilus spp.);
– Ictaluridae, such as bullheads and catfish (Ictalurus spp.).

Other fish that are important in their diet include sunfish (Lepomis spp.), darters (Etheostoma spp.), and perches (Perca spp.). These fish are often found in large groups. Bottom-dwelling fish, like Central mudminnows (Umbra limi) and sculpins (Cottus spp.), are also eaten because they stay still until predators are close. Game fish, such as trout (Salmonidae) and pike (Esocidae), are not eaten often because they are fast and can hide. However, otters may eat trout, pike, walleye (Sander vitreus vitreus), salmon (Oncorhynchus spp.), and other game fish during spawning. Otters have also been found to eat invasive Asian carp.

Adult North American river otters can eat 1.0–1.5 kilograms (2.2–3.3 lb) of fish each day. A study of captive otters showed they prefer fish that are 15–17 cm (5.9–6.7 in) long. They find it harder to catch fish that are smaller than 10 cm (3.9 in) or larger than 17 cm (6.7 in). Otters often eat larger fish on land and smaller fish in water.

North American river otters may eat more crustaceans, like crayfish (Cambarus, Pacifasticus, and others) and crabs, than fish if these are plentiful in their area during certain times of the year. In Georgia, crayfish made up two-thirds of the otters’ summer diet, and crayfish remains were found in 98% of summer scats. In winter, crayfish made up one-third of their diet. A study in Arkansas found that crayfish consumption, fish consumption, and water levels are connected.

During winter and spring, when water levels are high, otters eat more crayfish (73% of scats had crayfish remains) than fish. When water levels are low, crayfish hide, and fish become more concentrated and easier to catch. This makes fish more likely to be eaten by otters.

Amphibians and reptiles are part of the otters’ diet in areas where they are available, especially during spring and summer. Common amphibians and reptiles include frogs (Rana and Hyla), such as boreal chorus frogs (Pseudacris maculata), Canadian toads (Bufo hemiophrys), wood frogs (Rana sylvatica), American bullfrogs (Rana catesbeiana), green frogs (Rana clamitans), northwestern salamanders (Ambystoma gracile), California giant salamanders (Dicamptodon ensatus), rough-skinned newts (Taricha granulosa), and garter snakes (Thamnophis).

Amphibians and reptiles are easier to find during spring and summer because of breeding, warm temperatures, and enough water for these animals.

Waterfowl, rails, and some birds that nest in groups are sometimes eaten by otters. These birds are more likely to be caught during summer (when young birds are vulnerable) and autumn. Otters have been seen eating moulting American wigeon (Mareca americana) and green-winged teal (Anas crecca). Other birds in their diet include northern pintail (Anas carolinensis), mallard (Anas platyrhynchos), canvasback (Aythya valisineria), ruddy duck (Oxyura jamaicensis), and American coot (Fulica americana).

North American river otters do not eat bird eggs, even though they eat birds.

Aquatic invertebrates, like insects, are part of the otters’ diet. Otters eat more aquatic insects in summer when their numbers are high and they are easier to catch. Most invertebrates eaten by otters are dragonfly nymphs (Odonata), stonefly nymphs (Plecoptera), and adult beetles (Coleoptera). Some invertebrates found in otter scats or digestive tracts may have been eaten by fish first, which were then eaten by otters.

Mammals are rarely eaten by North American river otters and are not a major part of their diet. When they are eaten, they are usually small or live near water. Examples include muskrats (Ondatra zibethicus), meadow voles (Microtus pennsylvanicus), eastern cottontails (Sylvilagus floridanus), and snowshoe hares (Lepus americanus).

There are some reports that North American river otters eat

Threats

The dangers to North American river otters change depending on where they live. The presence of river otters is influenced by the type, spread, and number of water habitats, as well as how humans use the land. Before Europeans settled in North America, river otters lived in many water areas across the continent. However, trapping, the destruction or damage of wetlands, and the growth of industries like coal, oil, gas, tanning, and timber caused otter populations to disappear or shrink in many places. In 1980, a study found that river otters were completely gone in 11 U.S. states and had very few numbers in 9 other states. The biggest drops in otter numbers happened in inland areas where fewer water habitats supported fewer otters. While otter populations decreased in some parts of southern Canada, the only complete loss of otters in an entire province happened on Prince Edward Island.

In the 1970s, better methods for managing natural resources were developed, and people became more worried about the decline of river otter populations. As a result, wildlife agencies created plans to help otters recover, including programs to bring otters back to areas where they had disappeared. Since 1976, more than 4,000 otters have been reintroduced in 21 U.S. states. All Canadian provinces except Prince Edward Island, and 29 U.S. states, now have healthy otter populations that support yearly hunting. While current hunting practices do not harm otter numbers, hunting might slow the growth of otter populations in some areas.

Oil spills can harm otter populations, especially in coastal regions. Pollution and damage to water and wetland habitats may reduce where otters live and create long-term problems if water quality rules are not followed. Acid runoff from coal mines is a lasting water quality issue in some areas, as it harms the fish and other animals that otters eat. This problem stops otters from returning to or growing in certain areas. Recently, scientists have discussed the long-term effects of reintroducing otters on the remaining wild otter populations. Many threats to otters, such as pollution and changes to their habitats, have not been studied carefully. Few efforts have been made to understand how diseases affect wild otter populations, so this remains poorly known.

Conservation

Lontra canadensis is listed in Appendix II of CITES, an agreement that helps protect animals and plants from overexploitation. These otters have almost completely disappeared from many areas, especially in the midwestern and eastern United States. Appendix II includes species that are not currently at risk of extinction but could become endangered if trade is not carefully managed.

The North American river otter is classified as a species of least concern by the IUCN Red List because its population is not declining fast enough to be considered endangered. By the early 1900s, river otters had declined across much of their historic range in North America. However, improvements in water quality (due to clean water laws) and better management of animals hunted for their fur have allowed otters to return to many areas. Reintroduction projects, which involve bringing otters back to regions where they once lived, have helped restore populations in parts of the United States. Despite this, river otters are still rare or absent in the southwestern United States. In some areas, poor water quality and human development have slowed their recovery. The species is found in many regions, and conservation efforts have helped otters reestablish themselves in several places. However, reintroducing otters may cause problems by mixing the genes of native populations with those from other areas.