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 are 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 many sea otters, but people hunted them for their fur. After laws were made to stop hunting them, and with help from sea otter conservation, their numbers began to grow again. Today, sea otters live in about two-thirds of their old range, and this is seen as a big win for marine conservation. However, in some places, their numbers have not grown as hoped. Because of this, sea otters are still listed as an endangered species.

Evolution

The sea otter is the heaviest member of the weasel family. This family includes animals like weasels, badgers, and minks. Sea otters are different because they do not make dens or burrows. They can live their whole lives in the water.

Scientists once thought sea otters might be related to earless seals. But 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 sea animals, sea otters are very well adapted to life in the ocean. They have very thick fur—about 160,000 hairs per square centimetre—which helps keep them warm. They do not have blubber. Their oil glands 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 and measure 1.2 to 1.5 m long. Females are smaller, weighing 14 to 33 kg and measuring 1.0 to 1.4 m long.

Unlike most marine mammals, sea otters have no blubber. They stay warm with their very thick fur. Their fur is the densest of any animal, with many strands of hair close together. 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 water. They are excellent swimmers, using their hind feet to move 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.

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.

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.

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. 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.

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.

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.

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 greatly. 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 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 many sea otters near the Kuril Islands. After heavy hunting, numbers dropped greatly. By 2004, populations had recovered some, but recent surveys show 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. 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.

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 a lot each day because they use energy when they swim and hunt for food. They eat many kinds of sea creatures. Their favorite foods include sea urchins, sea stars, sea cucumbers, and shellfish like clams, mussels, and snails. In some places, they also eat fish and seabirds.

Sea otters are important for the ocean. They help keep the numbers of sea urchins down. Without sea otters, sea urchins can eat away kelp forests, which are homes for many sea animals. When sea otters are present, kelp forests stay healthy, helping the whole ocean. They also help protect coastlines by digging in the sand, which helps plants grow. Sometimes, sea otters can get sick from parasites.

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.

In the early 1700s, Russian hunters began catching sea otters 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. This began a period of intense hunting that lasted for many years. The Russians found sea otters more valuable than other furs.

Russian hunting 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 forced them to hunt. 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. Eventually, sea otter numbers became so low that hunting was no longer possible. By 1808, hunting had stopped in the Aleutian Islands. 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. 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. Hunting sea otters is now illegal except for limited harvests by indigenous peoples in the United States.

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. 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. 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. In California, sea otter numbers have fluctuated since the late 1990s, with high death rates among adults and subadults. Diseases and parasite infections have been major causes of death.

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 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.

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. 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.

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. 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.