Smooth-coated otters ©Getty Images

Smooth-coated otters ©Getty Images

Otters are part of the mammal family called mustelids, which includes ferrets, badgers, minks and weasels. There are 13 species, or kinds, of otter, on every continent except for Australia and Antarctica. 

Body and behaviours

Otters are playful, energetic animals. They are curious, and spend time investigating things, hunting, or playing with things they find. They are social, and play with each other, chasing or sliding down river banks or snow.

Rolling in the grass or against logs is fun, but it also is a way of keeping their fur in good condition. Some of their playful behaviour of rubbing on logs, rolling in piles of fallen leaves and rubbing their chests on bunches of leaves on bushes actually has a serious purpose:  they are ways of leaving scent to mark their territory.  

Otters communicate with each other using lots of different sounds, such as whistles and growls, chirps and barks: about a dozen or more different calls, each with its own distinct meaning such as alarm, greeting and mating calls. The Asian short-clawed otters are considered to be the most vocal of the otters. Otters are alert, and their sensitive whiskers can detect movement of any predators in the water. Depending on where they live, predators could include large cats and snakes, alligators or caimans, domestic dogs, or eagles. Sea otter predators include killer whales, sea lions and sharks. 

An otter underwater ©Getty Images

An otter underwater ©Getty Images

All otters are amphibious, which means they are equally at home on land and in the water. They  spend most of their time in the water, particularly sea otters, which spend only a little time on land.  Otters have long, streamlined bodies and long , flattish tails that move side to side to move them through the water.  They swim mostly on their backs or sides so they can see underwater and above. Most otter species have webbed feet, some more than others. Their back feet are used to steer them in the water. Otter species can stay under the water for  5 - 10 minutes, depending on the species. To do this, they slow down their heart rate so they use less oxygen. They close their nostrils and ears when they are underwater. 

Asian short-clawed otter feeding ©Getty Images

Asian short-clawed otter feeding ©Getty Images

Otters have two layers of fur. Close to their skin there is a thick layer of fur that traps air. There is an outer layer of longer fur that is waterproof. Otters must spend a lot of time grooming this top layer. If this layer becomes matted and clogged with oil or other substances, it could prevent the animal staying warm, and it would affect its hunting ability.

Diet

Otters find most of their food in the water.  They have long whiskers that help them find food even in murky water.  Some species use their hands to feel about in the mud or under rocks. As well as fish, freshwater otters hunt and eat frogs, crayfish, crabs and molluscs.  They occasionally eat a small bird or mammal.  They feed several times a day because they are such energetic animals. 

Sea otter diet includes sea urchins, abalone, octopus, snails, clams and mussels. They float on their backs, and crack open mussel and clam shells with a rock they hold on their stomachs.Sea otters eat about one quarter of their body weight each day.

Asian short-clawed otter at entrance of its holt ©Getty Images

Asian short-clawed otter at entrance of its holt ©Getty Images

Life Cycle

Otters live in groups consisting of a female, her older young, and her latest pups.  Males are more solitary or spend time with other males.   The females of most species give birth in a den, called a holt, to small, helpless, blind young called pups. After about a month, their eyes are open and they begin exploring the den. At about two months of age, they are taught to swim.  When they are about a year old, they are independent and head off on their own.

Sea otter pups are born in the water, with their eyes open, and have a special layer of fur so they can float even though they can't swim yet. They can swim at about two months of age, and until then they ride on their mother's chest to drink milk as she floats on her back.


Some otter species

A raft of sea otters in a bed of kelp ©Getty Images

A raft of sea otters in a bed of kelp ©Getty Images

The Sea Otter

The heaviest of the otter species.  Unlike other marine mammals, sea otters do not have a layer of blubber to keep them warm. Instead, the fur is very thick, the thickest of all animals.  The fur traps air bubbles to help keep them warm.  This amazingly thick, waterproof fur is the reason sea otters were once hunted almost to extinction. Today they are protected by law and their numbers have increased. 

Sea otters play a very important role in maintaining the balance in their near-shore marine environment, so important that they are considered to be a 'keystone' species.    Without the sea otters, undersea animals would eat all the coastal kelp (a kind of seaweed) forests that provide shelter and food for many species of animals. In addition, the movement of the kelp in the water is important  in stopping bacteria from developing, and in filtering carbon levels of the coastal ecosystems.  

Sea otter holding a rock that it uses to open shells ©Getty Images

Sea otter holding a rock that it uses to open shells ©Getty Images

An ecosystem is the interaction of living things with each other and with their environment.  An imbalance can destroy the ecosystem. In a healthy ecosystem, everything has its place.

Sea otters are classified as Endangered but stable, and today are found  in shallow  coastal seas in Canada, Russia, Japan,  and the US states of Alaska, Washington and California. Most are found in Alaskan waters. They can dive as deep as 100 metres, and can close their nostrils and ears when they do so.   Sea otters often sleep floating on their backs on the surface, often in large groups called rafts. They often float in the kelp forests, wrapping kelp around their bodies to anchor them in that spot.  When sleeping, sea otters are known to hold hands to keep from drifting apart while asleep.

The Asian small-clawed otter

Asian small-clawed otters ©Getty images

Asian small-clawed otters ©Getty images

They are the smallest of 13 species of otter,  known by a number of names including oriental small-clawed otter,  short-clawed otter or small-clawed otter. They are  found in north-western and south-western India; southern China including Hainan, a large island off the south China coast; the Malay Peninsula; the islands of Sumatra, Java, and Borneo; the Riau islands; and Palawan Island in the Philippines.

Their habitat  is next to rivers and streams, in wetlands, and estuaries (an estuary is a partly enclosed area of water with rivers running into it, and connected to the sea).  They are also at home in rice paddies and in mangroves. The term ‘mangrove’ refers to a both habitat and its plants. Mangrove swamps are found along tropical and subtropical coastlines, usually in bays protected from heavy waves, freshwater areas where rivers meet the sea. The evergreen trees and shrubs, also commonly called mangroves, thrive in mud or sand flats that are flooded daily with sea water. 

As the name suggests, the Asian short-clawed otter has small claws, unlike other otter species. The tiny claws do not protrude past the end of their nimble fingers. They have incomplete webbing between the fingers.  They are fast and agile both in the water and on land.  They can hold their breath underwater for about five minutes at a time. These otters choose territories in areas with equal amounts of land and running water.   Rice farmers are tolerant of these otters because they feed on crayfish that can damage rice fields.  Fishermen train otters to drive fish into nets.

The diet of Asian short-clawed otters is mainly crabs, other crustaceans, molluscs and fish. They also eat frogs, small mammals, snakes and insects.   Using their sensitive front paws, they dig around in the mud and under stones to find their prey. They hold their food in their hands as they eat, and although they crush the shells of crabs and molluscs with their strong back teeth, they are known to leave them in the sun for a while so that the shells open up in the heat.

Asian short-clawed otters are classified as Vulnerable. They are seriously threatened by rapid habitat destruction, hunting, and pollution.

The African clawless otter

On two toes on each of its back feet there are short claws for grooming, but otherwise they do not have claws or webbing between their toes. Their teeth are different from those of other otters,  adapted for crushing shellfish and the bones of large fish. They are found in a variety of habitats in Africa, including rainforests  and open plains in areas with water such as rivers, canals, reservoirs and lakes. They also live near beaches and shores and mangroves.  They are known to hunt in the sea and in freshwater. They are classified as of Least Concern.  

Giant otter in Peru ©Getty Images

Giant otter in Peru ©Getty Images

The giant otter

They are the largest of the otter species, but not as heavy as the sea otter.  They are found near slow-moving rivers, streams, lakes and swamps or rainforests in South American countries including Bolivia, Brazil, Colombia, Ecuador, Paraquay and Venezuela.  They are classified as Endangered. 

The hairy-nosed otter

This is a medium sized otter about which little is known. It is classified as 'Endangered, population decreasing'.  It is found in Sumatra (Indonesia)  and southern Thailand, southwest Cambodia and south Vietnam. It is possible there are some in Lao, Malaysia and other places in Indonesia.  It is thought their habitat is peat swamp forests and shallow coastal waters.  They are just over 1m long, have fully webbed feet and strong claws.

The Eurasian otter

Also known as European otter, nutria, common otter

A European otter ©Getty Images

A European otter ©Getty Images

This species have a wide range of habitats with nearby land area suitable for their resting and grooming, including coastal areas, rivers, streams, fjords, and ricefields. As long as they have fresh water to wash the salt off their fur, they also hunt in sea water. This species is the most widespread of the otters and are found from parts of Asia such as Sri Lanka and Indonesia, through Europe right up to the Arctic Circle, and in North Africa. They are the least social of the otters.

They are classified as Near Threatened, with threats including chemicals in water from run off from farms and sewage that affect the otters' food,  illegal hunting, increased fish farming in some areas has made otters to be considered a pest. They also face dangers from being caught in eel and fish traps and drowning, and being killed when crossing roads.

Read about and see videos of the Eurasian or European or common otter

http://www.arkive.org/common-otter/lutra-lutra/

Read about and see videos of the sea otter

http://www.arkive.org/sea-otter/enhydra-lutris/

Fun Fact: baby otters have to be taught how to dive and swim by their mothers!

Watch a zoo's baby otter being taught to swim by its mother