North American river otter

The North American river otter (Lontra canadensis), also known as the northern river otter and river otter, is a semiaquatic mammal that is endemic to the North American continent throughout most of Canada and along the coasts of the United States and its inland waterways. An adult North American river otter can weigh between 5 and 14 kilograms (11–31 lb). The river otter is protected and insulated by a thick, water-repellent coat of fur.

The North American river otter, a member of the subfamily Lutrinae in the weasel family (Mustelidae), is equally versatile in the water and on land. It establishes a burrow close to the water's edge in river, lake, swamp, coastal shoreline, tidal flat, or estuary ecosystems. The den typically has many tunnel openings, one of which generally allows the otter to enter and exit the body of water. Females give birth in these burrows, producing litters of one to six young.

North American river otters, like most predators, prey upon the most readily accessible species. Fish is a favored food among the otters, but they also consume various amphibians (such as salamanders and frogs), freshwater clams, mussels, snails, small turtles, and crayfish. The most common fish consumed are perch, suckers, and catfish.

The range of the North American river otter has been significantly reduced by habitat loss, beginning with the European colonization of the Americas. In some regions, though, their population is controlled to allow the trapping and harvesting of otters for their fur. North American river otters are very susceptible to the effects of environmental pollution, which is a likely factor in the continued decline of their numbers. A number of reintroduction projects have been initiated to help halt the reduction in their overall population.

Taxonomy and evolution

The North American river otter was first described by a German naturalist in 1777. It was named after Canada, where it was found. Today, it is known by many names, such as the northern river otter.

Scientists have studied the river otter’s family tree. They found that river otters and a related species called the giant otter split apart millions of years ago. These otters came to North America from an area that connected Asia and North America long ago.

Description

The North American river otter has long, thin whiskers that help it find food in dark water. Male otters are usually heavier, averaging about 11 kilograms (25 lb), while females average around 8 kilograms (18 lb). Their bodies range from 66 to 107 centimeters (26–42 inches) long, with about one-third of that length being their tail, which can be 30 to 50 centimeters (12–20 inches) long. Males can sometimes weigh more than 15 kilograms (33 lb). They look different from the Eurasian otter because they have longer necks, narrower faces, smaller spaces between their ears, and shorter tails.

Males and females also look different in other ways that are not related to their size.

North American river otters can live for 21 to 25 years when kept safe in captivity, but only 8 to 13 years in the wild.

Form and function

These otters often come close to boats or people on shore because they do not see very well, as their vision is better for underwater sight. They have a special clear eyelid called a nictitating membrane to protect their eyes while swimming.

Otters have 36 special teeth, including sharp canines and carnassials for catching prey, as well as large molars for crushing hard items like the shells of molluscs. They may also have extra premolars. The dental formula is 3.1.4.13.1.3.2.

Distribution and habitat

The North American river otter lives in many places in North America. You can find them in Canada, the Pacific Northwest, the Atlantic states, and along the Gulf of Mexico. They also live near the Pacific coast, in Alaska, and even on the Aleutian Islands.

Because of cities growing and pollution, these otters are not as common in some parts of the United States. But efforts to help them have worked well. For example, in Kentucky they came back in the 1990s and are now seen in many waterways. In Minnesota, they are doing better thanks to cleaner water and good habits by people.

Even though they are called river otters, they live in many types of water places, like lakes, rivers, wetlands, and coastlines. They need clean water and food to survive. They make their homes, called holts, in burrows or natural spaces like under logs or in riverbanks.

Behavior

North American river otters prefer places with plants, rocks, and good cover to live. They love to play, often wrestling with each other and chasing. This play helps them learn important skills like fighting and hunting.

These otters are active hunters in water and eat many kinds of animals that live in or near water. Fish are their main food all year, but they also eat crayfish, fruits, plants, birds, insects, small mammals, and more, depending on what is available. They do not eat dead animals they find.

River otters can live in areas up to 78 square kilometers, but usually stay in smaller spaces of about 8 to 39 square kilometers. They are friendly but can live alone. They are good at avoiding danger by diving and moving quickly. They play together a lot, which helps them make friends, learn to hunt, and show which areas they use. Mothers give birth to one to three babies in dens made by other animals. The babies start swimming after about two months and can live on their own by autumn, but often stay with their family until spring.

Ecology

The North American river otter eats a variety of foods, mostly fish, frogs, crayfish, turtles, insects, and small mammals. They hunt alone or in pairs, both on land and in water. These otters are good at catching animals that live in water.

Fish are a big part of their diet. They like to eat slow-swimming fish such as suckers, catfish, sunfish, and bass. They can eat up to 1 to 1.5 kilograms of fish each day.

They also eat crayfish, especially when it is available. In some places, crayfish make up a large part of their food, especially in the summer.

In spring and summer, they eat more frogs and other amphibians because these animals are easier to find. They also sometimes eat birds, like ducks, especially when the birds are nesting or molting.

Insects, such as dragonfly nymphs and beetles, are also part of their diet, mostly in the summer.

Mammals are not a big part of their diet, but they might occasionally eat small animals like muskrats or voles.

River otters have predators too. In water, they might face threats from animals like alligators, crocodiles, and killer whales, though these are rare. On land, predators include bobcats, cougars, coyotes, bears, and eagles.

Threats

Threats to North American river otter populations differ depending on where they live. Before Europeans settled in North America, river otters were common in many water areas. However, trapping, loss of wetlands, and industrial development caused many river otter populations to shrink or disappear in various places. By 1980, they were locally extinct in 11 U.S. states and had lost many members in 9 others. The hardest-hit areas were those with fewer water habitats.

In the 1970s, better ways to manage natural resources began, and people became more worried about declining river otter numbers. Wildlife agencies started projects to bring otters back, and since 1976, over 4,000 otters have been reintroduced in 21 U.S. states. Today, most Canadian provinces (except Prince Edward Island) and 29 U.S. states have healthy otter populations that can be hunted each year. While hunting does not threaten these populations overall, it might slow down their growth in some places.

Oil spills can harm otters, especially near coasts. Water pollution and loss of wetlands can also limit where otters can live and may cause problems in the long run if water quality rules are not followed. Acid drainage from coal mines harms water quality in some areas, removing food for otters and making it hard for their populations to grow. The effects of bringing otters back on the remaining populations and the risks from diseases are still not well studied.

Conservation

The North American river otter is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This means that while they are not currently in danger of disappearing, they could be if trade is not carefully managed.

In the early 1900s, river otter numbers dropped in many places because of poor water quality and hunting. Thanks to better water protection laws and careful management, their populations have grown again in many areas. Special projects have helped bring them back to parts of the United States where they had disappeared. However, they are still uncommon in the southwestern United States due to water quality and development issues.