Otter facts

•    There are 13 species of otter in total, ranging from the small-clawed otter, native to South and Southeast Asia, to the giant otter, which lives only in the rivers and creeks of the Amazon, Orinoco, and La Plata rivers in South America.
•    Sea otters have the densest fur of any other animal on Earth.¹ Their coat is packed with a million hairs per square inch in places (155,000 per square centimetre). A human head, for comparison, has between 800 to 1,290 hairs per square inch (124 to 200 hairs per square centimetre).² When they are born, sea otter pups float because of all the air trapped in their fluffy coats.
•    Otter poo, known as spraint, has a very unusual smell. According to the Sussex Wildlife Trust it has a ‘sweetish jasmine tea type smell, blended with a hint of fish’^.3
•    To stop themselves from floating away while they sleep, sea otters tie themselves up in kelp. They have even been known to entangle their feet with another otter so that they stay together.
•    Sea otters also use their paws as an eye mask when sleeping during the day.⁴
•    The North American river otter can hold its breath underwater for up to eight minutes.⁵
•    Sea otters often hold hands and groom each other, which helps them to bond with one another.
•    Some species of otter are solitary, whereas others live in groups. The most gregarious by far are sea otters, which form large social groups. When on water, these groups are called rafts, and the largest one ever recorded contained up to 2,000 sea otters.⁶
•    Otters do not build dams like beavers do, but sometimes otters may use an abandoned dam as part of their den, which is known as a holt.
•    Researchers have identified nine distinct calls made by sea otters, including distress screams and contented coos, as well as whines, whistles, growls, and snarls.⁷ 

There are 13 species of otter in total. They include the Congo clawless otter (Aonyx congicus), African clawless otter (Aonyx capensis), and Asian small-clawed otter (Amblonyx cinereus). The largest, the giant otter (teronura brasiliensis), is the biggest member of the weasel family and can reach 6 foot in length. It lives in and around the Amazon, Orinoco, and La Plata river systems in South America. Giant otters live in family groups, and hunt fish, crustaceans and even snakes.

The sea otter (Enhydra lutris), meanwhile, is native to the coasts of the North Pacific Ocean. Sea otters can be found in the waters off Russia, Alaska, British Columbia, Washington, and California. Their habitat includes rocky coastlines, thick kelp forests, and barrier reefs. Though they usually hunt alone, sea otters like to rest together and link arms in single-sex groups called rafts. A raft typically contains 10 to 100 sea otters, but the largest raft ever seen contained over 2000 animals.⁹

The Eurasian otter (lutra lutra) is found throughout Europe, Asia, and North Africa. This otter can survive in any unpolluted body of fresh water as long as there is enough food to eat.

One of the rarest members of the otter family is the Hairy-nosed otter (Lutra sumatrana). This otter is found in coastal areas and rivers across Southeast Asia, including in Myanmar, South Thailand, Cambodia, South Vietnam and Malaysia. This species of otter is under threat due to poaching. In Southeast Asia, hunters can receive up to $200 for each otter pelt.¹⁰

Other species of otter include the spotted-necked otter (Hydrictus maculicollis), smooth-coated otter (Lutrogale persipicillata, North American river otter (Lontra canadensis), South American river otter (Lontra provocax), neotropical river otter (Lontra longicaudis), and marine otter (Lontra felina).

Otters are carnivores, and expert hunters. Eurasian river otters feed mostly on fish such as trout, carp and eels.¹¹ However, they have also been known to raid riverbanks looking for waterbirds like moorhens or coots. They will also happily eat bird eggs, insects, amphibians, or even small mammals, and some have even been known to hunt snakes to supplement their usual diet of fish. On the Shetland Islands, some otters have even been known to abandon fishing and hunt rabbits instead.¹²

Sea otters, meanwhile, eat fish, crustaceans, and shellfish. Favoured seafood items include clams, mussels, crayfish, and crabs. Sea otters spend most of their day foraging in kelp forests, diving to the bottom of the seafloor on the lookout for tasty morsels. They need to consume up to 11kg of food every day to support their high metabolism – about a quarter of their own body weight.¹³ When they find a shellfish they have an ingenious method for opening it. The otter will float on its back, place a rock on its chest, then smash the shell down on it until it cracks open.

In Bennett Slough Culverts in California, sea otters have learnt to smash mussels against rocks on the seashore. The process leaves distinctive wear patterns on the rocks, and piles of broken shells fractured in a characteristic way. Researchers believe they can use these artefacts to uncover the two- 2-million-year evolutionary history of the sea otter and understand how prevalent tool use is in this animal.¹⁴

In parts of the ocean where food is scarce, sea otters also rely on tools like rocks and even glass bottles to help them smash open food that they wouldn’t normally eat.¹⁵ One study, in Monterey Bay, California, found that when otters’ favourite prey – urchins and abalone – run dry, the otters are forced to use tools to smash open hard-shell prey items, such as snails. The study analysed the behaviour of 196 otters in California and found that individual otters varied massively in the amount that they used tools. Female otters in particular used tools more, which allowed them to eat harder and larger prey. Using tools also protected the otters' teeth, giving those otters a distinct advantage over their non-tool using peers.

With webbed feet and powerful tails, otters are extremely strong swimmers. Their muscular bodies are streamlined to help them glide through the water, and they use their tails as rudders to help them steer. Otters can even close their nostrils and ears to help them keep water out. 

The speed of a swimming otter varies. Sea otters can reach nine kilometres per hour underwater, while North American river otters are faster at 11 kilometres per hour. The maximum speed of the giant river otter, meanwhile, is an impressive 14kph.¹⁶

Staying in the water for so long means that otters need unique adaptations to keep them warm. An otters’ fur is water repellent, and incredibly dense. However for the sea otter, which lives in cold oceans, this is not enough. Most marine animals are large and are kept warm by a thick layer of blubber below their skin. However sea otters are the smallest marine mammal, and don’t have any blubber. To help maintain their 37° Celsius (98.6° Fahrenheit) body temperature, sea otters have an extremely high metabolism.¹⁷ Their cells convert food into energy about three times as fast as one would expect in a mammal their size. To meet their energy demands they must consume one-fourth of their body weight in food every single day. 

They have another adaptation too. A 2021 study found that sea otters’ muscles are able to turn food directly into heat to help the animals stay warm in cold waters.¹⁸ The reason is down to the mitochondria – the powerhouse present in every single cell that converts food into energy the body can use. Mitochondria pump protons across their inner membrane as a way of storing energy that can be used later by the cell. However, in sea otters, the mitochondria are leaky. When a proton leaks back across the inner membrane, the energy is lost as heat. This explains why sea otters’ metabolism is so high – they need to keep eating to replace this lost energy. However the upside is that extra heat generated helps sea otters stay comfortable in 0 °C (32 °F) Pacific Ocean waters.

Otters can be found living on every continent except Antarctica and Australia. Some, such as the giant otter thrive in the mighty Amazon, while others such as the smooth coated otter, lives in the heart of Singapore.

The Eurasian river otter makes its home in the freshwater rivers, canals, lakes, and wetlands of Europe, Asia, and Africa. The sea otter and marine otter, meanwhile, lives in the shallow coastal waters of the Northern Pacific Ocean.

In the UK, otter hotspots include Scotland, the west coast of Wales and Southwest England. Otters will thrive wherever there is clean freshwater with plenty of available food such as fish. They like clean water, and so pollution in UK rivers is may be a factor contributing to the decline of otter populations.¹⁹ Otters also like to live in areas of the riverbank that have secluded areas of vegetation in which they can raise their young.

They make their nests - also known as holts - in natural nooks and crevices found in riverbanks, tree roots, shrubs and rocks. They line their homes with grasses, ferns, reeds and leaves, and have multiple entrances, including underwater passages.

Otters are by in large sociable animals that love to spend their time in family groups. When in those groups there’s nothing they love more than to play. Otters have been observed wrestling, sliding down riverbanks, bouncing pebbles on their paws in a manner akin to juggling, and even playing games of tag.²⁰ For example, one study found that some captive North American river otters engage in 15 to 20 bouts of wrestling per hour.²¹

Both wild and captive otters appear to love sliding around on mud and ice. One study used remote video cameras to monitor a population of river otters reintroduced to the Youghiogheny River in southwestern Pennsylvania.²² The researchers observed a group of three wild otters sliding repeatedly down snowbanks. Collectively, the otters slid 16 times in 53 seconds.

Another commonly observed play behaviour in various otter species is ‘rock juggling’, where otters rapidly pass an object between their forepaws and sometimes their mouth. Otters can perform rock juggling while lying down or standing upright. One study observed rock juggling in Asian small-clawed (Aonyx cinereus) and smooth-coated (Lutrogale perspicillata) otters.²³ It found that juvenile and senior otters juggled more than adults.

Although they look cute and have a playful nature, otters can be aggressive towards humans if approached. If an otter feels threatened, it can use its heavy muscular body and sharp claws to overpower pets and even small children. Otters can also bite, and transmit diseases such as rabies, tetanus, or salmonella, so you should seek medical attention if you are scratched or bitten by one.²⁴

Otters are certainly loveable and fun creatures to observe. However, their wild nature means they shouldn’t be kept as pets. In fact, in countries such as the UK, US and Japan it’s illegal to own a native otter as a pet.²⁵ Despite this, otters are illegally traded and bought as pets in many Asian countries like Japan, Thailand, and Malaysia.²⁶ A report by World Animal Protection found that otters suffer greatly in captivity.²⁷ For example, wild otters spend their lives in and around water, an environment pet owners cannot replicate with time spent in a bathtub, paddling pool, or bucket.  In the wild, some species of otters live in large groups, but as pets they tend to live largely in isolation. As a result, captive otters display undesirable behaviours, and can be loud, destructive and inflict nasty bites. Meanwhile a lack of space and stimulation can also lead to abnormal repetitive behaviours like over-grooming, pacing, aggression or lethargy. 

The lifespan of an otter varies hugely depending on the species, and whether the animal lives in the wild or in captivity. For example, male sea otters live an average of 10 to 15 years in the wild, while females live slightly longer, between 15 to 20 years.²⁸ The oldest sea otter in captivity, meanwhile, was Etika, who lived to be about 28 years old at the Seattle Aquarium.²⁹

The Eurasian otter, on the other hand, can live as long as 20 years in captivity, and 9-10 years in the wild.³⁰ However most Eurasian otters don’t live this long. One study in Scotland looked at the cause of death of Eurasian otters in Shetland, and found that the mean adult life expectancy was just 3.1 years.³¹ Most of the otters in this study died from starvation, although accumulation of toxins such as mercury could have played a secondary role.

For your best chance at finding Eurasian otters in the UK, here’s what you should do: Otters are most active at night, so dawn and dusk are good times to go out looking for them. Head to a riverbank, canal, or lake, and look for otter tracks in the mud and sand close to the water. Otters have five toes, and you may be able to see webbing in their pawprints. You could also look for otter droppings, known as spraints. Spraints are a greenish, black-grey colour, and they smell sweet and musky. They also may contain fragments of bones, shells, or feathers and fur. Finally, to find otters in the water you should look out for the bubbles they leave when they dive, or the V-shaped wake they leave behind them when they swim. You might also catch a glimpse of the splash they tail makes as they dive underwater looking for food.³²

Sea otters are an example of what is called a keystone species – an organism that helps keep the ecosystem in which it lives healthy.

In the 1900s, the sea otter was almost hunted to extinction due to the demand for its thick, rich pelt (skin and fur). In the 1970s James Estes, an American marine biologist, compared the sea floors around the Andalusian islands where sea otters had disappeared with those where they remained.³³ He found that in islands that lacked sea otters, the numbers of sea urchins had increased significantly. However, intriguingly, the kelp forests that once grew around those islands had disappeared. This makes sense, because sea urchins eat kelp. In contrast, the islands where sea otters had survived had less sea urchins, but were surrounded by lush kelp forests. Estes concluded that by keeping the population of sea urchins down, sea otters were helping the kelp forests to thrive.³⁴

As well as serving as a food source for many, kelp forests serve as crucial habitats for small creatures such as fish, worms and small crustaceans. Importantly, kelp forests also play a key role in absorbing carbon dioxide from the oceans, helping to mitigate the harmful effects of climate change. 

Featured image © Lilian Dibbern | Unsplash

Fun fact image © Ray Harrington | Unsplash

Quick facts:

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