Sea otter

The sea otter (Enhydra lutris) is a marine mammal that lives along the coasts of the northern and eastern North Pacific Ocean. Adult sea otters weigh between 14 and 45 kg, making them the heaviest members of the weasel family, but they are still among the smallest marine mammals. What makes sea otters special is their thick coat of fur, which is the densest fur in the animal world. Though they can walk on land, sea otters are able to live their whole lives in the ocean.

Sea otters live close to the shore and dive to the sea floor to forage. They mainly eat marine invertebrates like sea urchins, different kinds of mollusks, and crustaceans, and sometimes fish. One interesting habit is that they often use of rocks to break open shells or to get food out of hiding places, making them one of the few animals that use tools. In many places, sea otters help keep the balance of nature because they eat sea urchins, which, if left unchecked, can damage big areas of kelp forest ecosystems.

There were once between 150,000 and 300,000 sea otters, but people hunted them for their fur from 1741 to 1911. By the end of that time, only about 1,000 to 2,000 sea otters were left, living in just a part of where they used to live. After laws were made to stop hunting them, and with help from sea otter conservation and efforts to bring them back to places they used to live, their numbers began to grow again. Today, sea otters live in about two-thirds of their old range, and their recovery is seen as a big win for marine conservation. However, in places like the Aleutian Islands, California, and Russia, their numbers have not grown as hoped. The same is true in Japan, where there are still very few sea otters. Because of this, sea otters are still listed as an endangered species.

Evolution

The sea otter is the heaviest member of the weasel family, which includes animals like weasels, badgers, and minks. Unlike other weasels, sea otters do not make dens or burrows and can live their whole lives in the water. Scientists once thought sea otters might be closely related to earless seals, but genetic studies show they share a common ancestor with other otters about 5 million years ago.

Fossils show that sea otters evolved in the North Pacific Ocean around 2 million years ago. They later spread to places like the Aleutian Islands, Alaska, and along the North American coast. Even though they entered the water more recently than some other marine animals, sea otters are very well adapted to life in the ocean. They have extremely thick fur—about 160,000 hairs per square centimetre—which helps keep them warm since they do not have blubber. Their oil glands also help keep their fur tightly packed and free of air.

Description

The sea otter is one of the smallest marine mammal species, but it is the heaviest member of the weasel family. Male sea otters usually weigh between 22 to 45 kg (49–99 lb) and measure 1.2 to 1.5 m (47–59 in) long. Females are smaller, weighing 14 to 33 kg (31–73 lb) and measuring 1.0 to 1.4 m (39–55 in) long.

Unlike most marine mammals, sea otters have no blubber and instead rely on their extremely thick fur to stay warm. Their fur is the densest of any animal, with up to 150,000 strands of hair per square centimetre (970,000/in²). This fur helps keep them warm by trapping air close to their skin. Sea otters also have long, sensitive whiskers and front paws that help them find food, even in dark or murky water. They are excellent swimmers, using their hind feet to propel themselves underwater.

Behavior

The sea otter is active during the day. It hunts for food and eats in the morning, rests in the middle of the day, hunts again in the afternoon, and may hunt a third time around midnight. Females with babies often hunt more at night. Sea otters spend a lot of time cleaning their fur, which helps keep them warm.

Sea otters often roll around in the water while eating, which helps wash food scraps from their fur.

Foraging

See also: Physiology of underwater diving

Sea otters hunt by diving into the water, often to the sea floor. They can hold their breath for up to five minutes, but most dives last about one minute. Sea otters are special because they can lift and turn over rocks with their front paws to find food. They also grab snails from kelp and dig in mud for clams. They catch fish with their paws, not their teeth.

Sea otters have a loose pouch of skin under each front leg where they store food and sometimes rocks to crack open shells. When they come to the surface, they float on their backs and eat using their front paws to tear food apart. They can swallow small mussels whole, even with their shells, or twist apart larger shells. To eat sea urchins, they bite through the spines to get to the soft inside.

See also: Tool use by sea otters

Sea otters use rocks as tools when hunting and eating. They may pound their food against a rock to open hard shells, or hammer at abalone to get it off rocks.

Social structure

Even though adult sea otters hunt alone, they often rest together in groups called rafts. These groups usually have 10 to 100 sea otters, with male groups being larger than female ones. The biggest raft ever seen had over 2000 sea otters. To stay close to shore while resting, sea otters often wrap themselves in kelp.

Male sea otters are more likely to mate if they have a territory that females also like. Males usually defend their territory from spring to autumn, when mating is most common. Females move between male territories and outnumber males. Males without territories gather in large groups and swim through areas with females to find mates.

Sea otters make many sounds. Baby sea otters cry like gulls. Happy females make cooing sounds, while males may grunt. Scared or upset sea otters may whistle, hiss, or scream.

In zoos, sea otters have been seen forming close bonds with each other.

Reproduction and life cycle

Sea otters have many mates. Males look for females in their territory or find females that are ready to mate. When a male finds a female, they play together and stay together for three days. The male holds the female’s head with his jaws while mating, and this can leave scars on the females.

Babies are born any time of the year, with most born between May and June in the north and between January and March in the south. After about four to twelve months, the baby is born in the water. Most babies are born alone, but sometimes twins are born, though usually only one survives. Baby sea otters can see, have teeth, and are covered in thick fur at birth. Mothers clean and care for their babies for hours. The baby’s fur holds so much air that it floats on the water.

Mothers nurse their babies for six to twelve months. The milk is rich in fat. Baby sea otters learn to swim and dive with their mothers’ help. Young sea otters start by bringing up things like starfish and pebbles. Babies are usually independent after six to eight months, but sometimes stay with their mother longer. Many baby sea otters do not survive their first winter.

Females take care of the babies. Mothers are very devoted to their pups, keeping them close and grooming them often. When hunting, mothers leave their babies floating on the water, sometimes wrapped in kelp. If the baby is not sleeping, it cries until the mother returns. Mothers have been known to carry their dead pups for days.

Females can have babies at three or four years old, and males at five. In the wild, sea otters live up to 23 years, with females often living longer than males. The oldest known sea otter lived to be 28 years old in a zoo.

Population and distribution

Sea otters live in coastal waters that are 15 to 23 metres deep and usually stay within a kilometre of the shore. They are most often found in areas protected from strong ocean winds, such as rocky coastlines, thick kelp forests, and barrier reefs. Their northern range is limited by ice, as sea otters can survive near drift ice but not land-fast ice. Individuals typically stay in a home range a few kilometres long for their whole lives.

The sea otter population was once between 150,000 and 300,000, stretching from northern Japan to central Baja California Peninsula in Mexico. The fur trade that began in the 1740s reduced their numbers to just 1,000 to 2,000 in 13 colonies. Today, sea otters are recovering in parts of their former range, with stable populations in places like Russia, Alaska, British Columbia, Washington, and California. However, recent counts in areas like the Aleutian Islands and the Sea of Okhotsk have shown steep declines.

Japan

In Japan, sea otters were hunted along the northern coast, including Hokkaido. The last count estimated around 50 sea otters living off the coast of eastern Hokkaido. Efforts are being made to monitor and protect this small population.

Russia

Most Asian sea otters live along the Russian Far East coastline, including areas like Kamchatka and Sakhalin Island. Before the 19th century, there were around 20,000 to 25,000 sea otters near the Kuril Islands. After heavy hunting, numbers dropped to just 750. By 2004, populations had recovered to about 27,000, but recent surveys show steep declines, likely due to continued illegal poaching.

British Columbia

In British Columbia, a small group of sea otters survived near Vancouver Island. By 2013, their numbers had grown to over 5,600, and they continue to increase. Another group was discovered in central British Columbia in 1989, and by 2013, it had grown to over 1,100 individuals.

United States

Alaska

Alaska has the largest sea otter population. In 1973, there were between 100,000 and 125,000 sea otters, but by 2006, this number had fallen to about 73,000. A big drop in the Aleutian Islands is mostly to blame, though orca predation is suspected as a factor. The population in Prince William Sound was also hurt by the Exxon Valdez oil spill in 1989.

Washington

In the late 1960s, 59 sea otters were moved from Amchitka Island to Washington. Their numbers dropped at first but have since grown to over 2,000. They are mostly found along the outer coasts, though there have been a few sightings in the San Juan Islands and Puget Sound.

Oregon

The last native sea otter in Oregon was likely killed in 1906. In the 1970s, 95 sea otters were moved from Alaska to Oregon, but they disappeared again. There have been a few recent sightings, including one in Depoe Bay in 2009.

California

California’s sea otter population today comes from a small group of about 50 otters found near Bixby Creek Bridge in 1938. Their range has slowly expanded from Pigeon Point in San Mateo County to Santa Barbara County. Efforts to establish a reserve population on San Nicolas Island were successful, though most otters returned to the mainland. The population has grown but faced challenges from toxins in their food and increased shark attacks.

Mexico

Sea otters were once common along the Baja California Peninsula but were hunted to extinction by the early 1900s. Recent sightings suggest a small number may have returned, possibly from populations in California.

Ecology

Sea otters need to eat at least 20% of their body weight each day because they use a lot of energy when swimming and hunting for food. They are top hunters and eat over 100 different kinds of sea creatures. Their favorite foods include sea urchins, sea stars, sea cucumbers, and many types of shellfish like clams, mussels, and snails. In some places, they also eat fish, seabirds, and even giant octopuses.

Sea otters are very important for the ocean because they help keep the numbers of sea urchins down. Without sea otters, sea urchins can eat away kelp forests, which are important homes for many sea animals. When sea otters are present, kelp forests stay healthy, helping the whole ocean ecosystem. They also help protect coastlines by digging in the sand, which helps plants grow and reduces erosion. Unfortunately, sea otters can get sick from parasites that come from human activities.

Relationship with humans

Fur trade

Sea otters have very thick fur, which made them targets for hunters for many years. Indigenous peoples have hunted sea otters for food and fur for thousands of years. Large-scale hunting began in the 18th century when traders from around the world arrived to meet the demand for otter pelts, one of the most valuable types of fur.

In the early 1700s, Russian hunters began catching sea otters in the Kuril Islands and selling them. Russia explored the northern Pacific and sent Vitus Bering to map the Arctic coast. In 1741, Bering was shipwrecked on Bering Island, where his crew discovered sea otters and hunted them. This began a period of intense hunting that lasted for many years. The Russians found sea otters more valuable than other furs they had hunted before.

Russian hunting soon reduced sea otter numbers in the Commander Islands, and by 1745 they moved to the Aleutian Islands. They traded with the Aleut people at first but later took hostages and forced them to hunt. Many Aleuts died from diseases brought by the hunters or were killed. By the 1760s, Russia had reached Alaska. In 1799, Tsar Paul I created the Russian-American Company to control the fur trade. Later, under Aleksander I, the company was placed under the Imperial Navy due to concerns about how indigenous peoples were treated.

Other countries also joined the hunt. Spanish explorers in what is now Mexico and California bought pelts from Native Americans and sold them in Asia. In 1778, British explorer Captain James Cook reached Vancouver Island and bought furs from local people. When his ship stopped in a Chinese port, the pelts sold for high prices and became known as "soft gold." People from all over Europe and North America came to the Pacific Northwest to trade for sea otter furs.

Russian hunting moved south, with American ship captains helping. Between 1803 and 1846, 72 American ships hunted otters in California, taking about 40,000 pelts. The Russians founded a settlement at Fort Ross in northern California in 1812. Eventually, sea otter numbers became so low that hunting was no longer possible. By 1808, hunting had stopped in the Aleutian Islands. Further restrictions were ordered in 1834. When Russia sold Alaska to the United States in 1867, the population had recovered to over 100,000, but American hunters began hunting them again. Prices rose as otters became rarer. By the 1880s, a pelt could sell for $105 to $165, and by 1903, some pelts were worth $1,125. In 1911, several countries signed a treaty to stop hunting sea otters. So few remained that many thought the species might disappear completely.

Recovery and conservation

In the 20th century, sea otter numbers increased in about two-thirds of their historic range, which is considered one of the greatest successes in marine conservation. However, the IUCN still lists the sea otter as an endangered species. Major threats include oil pollution, attacks by orcas, poaching, and conflicts with fisheries—sea otters can die if caught in fishing gear. Hunting sea otters is now illegal except for limited harvests by indigenous peoples in the United States.

Poaching was a concern in the Russian Far East after the collapse of the Soviet Union in 1991, but it has decreased with better law enforcement and improved economic conditions.

The biggest threat to sea otters is oil spills. Because they rely on their fur to stay warm, oil damages their insulation and can cause death from hypothermia. Oil can also harm their liver, kidneys, and lungs. The Exxon Valdez oil spill in 1989 killed thousands of sea otters in Prince William Sound, and oil continued to affect the population there for years.

Sea otter populations in California, Washington, and British Columbia are small, so a single major oil spill could be disastrous. Conservation efforts focus on preventing oil spills and preparing to rescue otters if one happens. Increasing sea otter populations would also reduce the risk of a spill wiping out an entire group. However, some people who depend on shellfish fishing have opposed allowing sea otter ranges to grow because otters eat shellfish.

After the fur trade, sea otter numbers dropped greatly, leading to low genetic diversity. Recent efforts to increase their numbers have helped California’s population grow to around 3,000, though this is still far below pre-fur trade numbers. Northern sea otters have returned to pre-fur trade levels along parts of the coast. Conservation methods include breeding programs and protected areas.

In the Aleutian Islands, sea otter numbers dropped suddenly in recent decades. The most accepted theory is that orcas began eating them, though there is no direct evidence. In California, sea otter numbers have fluctuated since the late 1990s, with high death rates among adults and subadults, especially females. Diseases like Toxoplasma gondii and parasite infections have been major causes of death. The Toxoplasma gondii parasite comes from cats and may spread through sewage.

Sea otter habitats are protected in several areas in the United States, Russia, and Canada. For example, about 1,200 sea otters live in the Monterey Bay National Marine Sanctuary, and more than 500 live in the Olympic Coast National Marine Sanctuary.

Economic impact

Some of the sea otter’s favorite foods, like abalone, clams, and crabs, are also important to people. In some places, people have blamed sea otters for drops in shellfish harvests. However, shellfish declines have also happened in areas without sea otters and may be due to overfishing, disease, pollution, and natural events. Sea otters and abalone fisheries cannot coexist in the same area, and the same is likely true for some other shellfish.

Sea otters help the kelp forest ecosystem by controlling sea urchin populations. Kelp is used to make food and medicines. Sea otters also control red king crab populations and invasive species like the European green crab. In some areas, sea otters are popular tourist attractions, bringing visitors to local businesses. Studies have shown that people are willing to pay more to see sea otters or know they exist nearby.

Roles in human cultures

For many indigenous cultures in the North Pacific, the sea otter has been important for both cultural and material reasons. These cultures often have stories and legends about the sea otter, sometimes seeing it as close to human. For example, the Nuu-chah-nulth, Haida, and other First Nations used sea otter pelts as regalia for chiefs. The Aleut people carved sea otter bones for ornaments and games and used powdered sea otter bone as medicine.

In recent decades, sea otters have become popular in Japan and appear in manga and literature. In American literature, sea otters have appeared in stories where they help preserve knowledge if humans disappear.

Aquariums and zoos

Sea otters do well in captivity and are featured in many public aquariums and zoos. The Seattle Aquarium was the first to raise sea otters from birth to adulthood, with the birth of Tichuk in 1979. Videos of sea otters have drawn millions of viewers online. For example, a video of two sea otters holding paws at the Vancouver Aquarium received over 22 million views. During the COVID-19 pandemic, a livestream of a rescued sea otter pup named Joey at the Marine Mammal Rescue Center attracted millions of viewers worldwide. In 2024, a video of another pup named Tofino received over 120 million views on Instagram.

Current conservation

Sea otters are important to ecosystems and need protection from threats like oil spills, overfishing, and getting caught in fishing gear. Laws like the North Pacific Fur Seal Convention of 1911, the US Endangered Species Act of 1973, and the US Marine Mammal Protection Act of 1972 help protect them. Conservation also includes breeding programs and protected areas. Sea Otter Awareness Week is held every year during the last full week of September to highlight the importance of sea otters and the challenges they face.