Sea otter conservation started in the early 1900s when sea otters were almost gone because of hunting for their valuable fur. Sea otters were once common in a wide area across the North Pacific Ocean, from northern Japan to Alaska to Mexico. By 1911, hunting had reduced their numbers to fewer than 2,000, mostly in remote and hard-to-reach places. The IUCN lists the sea otter as an endangered species. Threats to sea otters include oil spills, and one large spill can quickly kill thousands of them.
During the 20th century, sea otter populations began to grow again from small groups in eastern Russia, western Alaska, and California. Starting in the 1960s, efforts to move sea otters back to areas where they once lived helped restore their numbers along the west coast of North America. Some populations are now healthy, and the recovery of sea otters is considered one of the most successful examples of marine conservation. This recovery helped sea otters earn the title of a keystone species. They are called a keystone species because they help protect kelp forests, which support many other sea animals.
However, in three important areas, sea otter numbers have recently dropped or stayed low. In the Aleutian Islands, a large and unexpected loss of sea otters has happened since the 1980s. The cause is unknown, but the pattern matches increased predation by orcas. In Russia, sea otter numbers have dropped sharply, and illegal hunting is suspected. In California, sea otter numbers stopped growing in the 1990s, likely for different reasons than in Alaska. Many sea otters have died from diseases found in young and adult otters. A parasite that can kill sea otters is found in the feces of wild and domestic cats. Another problem is oil spills, which are dangerous to sea otters because they coat the animals’ fur, which they use to stay warm. If oil breaks this insulation, sea otters can die from cold.
Background
The sea otter (Enhydra lutris) is a marine mammal that lives near the shores of the North Pacific, from northern Japan, the Kuril Islands, and Kamchatka east across the Aleutian Islands and along the North American coast to Mexico. It has the thickest fur of any animal in the world. Between 1741 and 1911, a period of heavy hunting for sea otter pelts, called "the Great Hunt," reduced the global population to 1,000–2,000 individuals, covering only a small part of the species’ historic range. Since then, most commercial hunting has been banned, though some limited hunting by indigenous peoples is allowed.
The sea otter mainly eats invertebrates such as sea urchins, mollusks, crustaceans, and some fish. In most of its range, it is a keystone species, meaning it has a major impact on its ecosystem that is much larger than its size or number. Sea otters control sea urchin populations, preventing the formation of "urchin barrens" and allowing kelp forests to grow. Without sea otters, kelp forests would suffer serious damage, harming the inshore species that depend on them. Kelp forests absorb carbon from the atmosphere, making them important for climate change. If kelp forests decline due to too many sea urchins, climate change could become even worse. Kelp forests also provide shelter for many fish and marine animals, showing how important sea otters’ diet is for marine life.
Because of the sea otter’s important role in the ecosystem and its cultural and aesthetic value, efforts have been made to protect it and expand its range. Conservation is difficult because some of the sea otter’s prey, such as abalone, crabs, and clams, are also eaten by humans. Some people who harvest shellfish for commercial, recreational, or subsistence purposes have opposed expanding the sea otter’s range, and there have been cases of fishermen illegally killing them.
The sea otter’s range is currently not continuous. It is missing from about one-third of its former range, including all of Oregon and northern California. It has only recently started to return to Mexico and northern Japan. Sea otters can thrive in captivity and are found in over 40 public aquariums and zoos. The southern sea otter, which once lived from Baja, California, to Oregon and Washington, now only lives from Southern California to just north of Half Moon Bay, California. Its population was once much larger but now numbers just over 3,000 as of a 2006 census. The largest groups of sea otters are found near Alaska. While the northern sea otter population in this region has declined, it has not been affected as severely as the southern population.
Conservation issues
Research by the U.S. Geological Survey shows that the amount of food available is the main factor affecting how quickly sea otter populations grow. The IUCN lists major threats to sea otters as oil pollution, attacks by orcas, illegal hunting, and conflicts with fishing activities. Sea otters can drown if they become tangled in fishing nets. They can also become stressed when people get too close while watching them. The biggest threat to sea otters is oil spills. Unlike most other sea animals, sea otters have very little fat under their skin. Instead, they rely on their fur to stay warm. Their fur must stay clean, thick, and water-resistant to trap air and keep them insulated from cold water. When oil covers their fur, it stops the fur from trapping air. Oil can also harm the liver, kidneys, and lungs of sea otters when they breathe it in or swallow it while grooming. This damage, along with the loss of insulation from their fur, can cause sea otters to freeze to death.
Sea otters live in small areas along the coasts of California, Washington, and British Columbia. A single large oil spill in these regions could cause a major loss of sea otters. Preventing oil spills and preparing to rescue otters if a spill happens are important parts of conservation work. Making sea otter populations larger and covering more areas can help reduce the harm caused by oil spills.
Sea otters need to produce a lot of body heat to stay warm because they lack blubber. To meet this need, they must eat food equal to 25% of their body weight each day. Finding food can take 20% to 50% of their day, depending on where they live, whether they are raising young, and how much prey is available. This time spent hunting makes them more at risk from dangers.
Marine protected areas are places where harmful activities, like oil drilling and waste disposal, are not allowed. These areas provide safe homes for sea otters. For example, the Monterey Bay National Marine Sanctuary has more than 1,200 sea otters, and the Olympic Coast National Marine Sanctuary has over 500.
Over the past 60 years, research has helped increase sea otter numbers from a few thousand each year at the start of the 20th century to about 150,000 each year today. Scientists have identified several challenges for future sea otter protection. These include: (1) studying sea otter populations in smaller areas to better understand how they move; (2) learning how food availability and ecosystem health affect their numbers; (3) creating monitoring programs with help from scientists worldwide to improve research over time and space; (4) studying the costs and benefits of expanding sea otter populations to avoid problems like overpopulation; (5) understanding how sea otters are sometimes affected by larger predators. Scientists are using quantitative models to help analyze data about sea otters’ health, behavior, and population changes. These models help test ideas quickly and create clear ways to understand how sea otter populations grow and change.
Russia
Before the 19th century, there were about 20,000 to 25,000 sea otters in the Kuril Islands, with more living on Kamchatka and the Commander Islands. After the Great Hunt, which lasted many years, the population in these areas, now part of Russia, dropped to only 750. By 2004, sea otters had returned to all of their old homes in these regions, with an estimated total of about 27,000. Of these, about 19,000 lived in the Kurils, 2,000 to 3,500 on Kamchatka, and 5,000 to 5,500 on the Commander Islands. The recovery of sea otters in Russia was helped by long-term protection, expanding their living areas, and people moving away from the islands.
However, recent counts from 2019 to 2024 show large drops in sea otter numbers across all regions, which questions earlier estimates. The latest numbers show about 3,000 sea otters near the Kuril Islands, and 1,673 and 1,565 near the Commander Islands and Kamchatka peninsula, respectively. Continued illegal hunting is believed to be a major cause of these drops. In Russia, groups like the Nature and People Foundation have worked harder to raise awareness about the challenges facing the sea otter population.
Japan
Sea otters have been seen in the waters near Cape Nosappu, Erimo, Hamanaka, Nemuro, and other places in the region. The most recent count found about 50 sea otters living along the coast of eastern Hokkaido. The Etopirika Foundation, a small nonprofit group led by Yoshihiro Kataoka, tracks the local sea otter population and studies ways to help protect them. In April 2025, Kataoka recorded the first known case of deadly avian influenza in a sea otter.
Alaska
Colonies were found near Alaska's Aleutian Islands and Prince William Sound in the 1930s. A sanctuary was created on Amchitka Island, where the sea otter population grew so much that there were not enough prey for them. By the mid-1960s, Amchitka Island was used as a site for nuclear testing, which caused many sea otters in the area to die. Before a major test in 1968, the U.S. Atomic Energy Commission decided to move hundreds of the animals to other parts of the coast. Between the 1960s and 1970s, 700 sea otters were relocated. Scientists learned better ways to safely transport the animals, which improved their survival rates. In 1973, the sea otter population in Alaska was estimated to be between 100,000 and 125,000 animals. That year, the U.S. Departments of Interior and Commerce introduced the Endangered Species Act of 1973 (ESA) to protect plants and animals in the United States, other countries, and the ocean.
In the 1980s, the Aleutian Islands in western Alaska were home to about 55,000 to 100,000 sea otters. By 2000, their population dropped to around 6,000 animals. One idea is that orcas, a type of large ocean predator, may have been hunting the otters. Evidence for this is not direct: Few sick or very thin otters have been found, suggesting disease or starvation is unlikely. Also, otter numbers dropped in areas where orcas live, but not in nearby lagoons where orcas are not present.
Some orcas in Alaska eat marine mammals, such as seals, sea lions, and small whales, while others prefer fish. Sea otters are small and provide little food for orcas. However, if a few orcas hunted otters regularly, they could cause large numbers of otters to disappear. One theory suggests that orcas may have started eating otters because their usual prey, like large whales, became scarce due to commercial whaling in the 1960s. Later, seal and sea lion populations declined in the 1970s and 1980s, possibly forcing orcas to hunt smaller prey. This idea remains debated, as no direct proof has been found that orcas prey on sea otters in large numbers.
In March 1989, the Exxon Valdez oil spill severely harmed the sea otter population in Prince William Sound. Over 1,000 oil-covered otter bodies were found, though the actual number of deaths was likely much higher. About 350 oiled otters were rescued and given special care for five months. Each otter was sedated, cleaned, and dried. Those that had swallowed oil were treated with activated charcoal. Around 200 of the 350 rescued otters survived, but many died later after being released. While few otters were saved, the effort helped scientists learn better ways to care for oiled otters. A 2006 report stated that sea otters are still affected by oil remaining in the area from the spill.
As of 2006, there were about 73,000 sea otters in Alaska. In August 2005, the "southwest Alaska Distinct Population Segment" of the sea otter was listed as "threatened" under the Endangered Species Act. Less than a year later, the Arizona-based Center for Biological Diversity filed a lawsuit, saying the U.S. Fish and Wildlife Service did not set aside critical habitat for the species, as required by the Endangered Species Act.
British Columbia and Washington
Between 1969 and 1972, 89 sea otters were moved by airplane or boat from Alaska to the west coast of Vancouver Island, British Columbia. These otters formed a healthy population, which grew to over 3,000 by 2004. Their range now includes areas from Tofino to Cape Scott. However, the First Nations people in the region were not asked for their opinions before the otters were relocated. While the otters helped improve the health of the ecosystem, they reduced the number of shellfish and sea urchins that local Indigenous communities relied on for food. Many in these communities later felt regret about the otters returning.
In 1989, a group of sea otters was found living on the central coast of British Columbia. It is unclear whether this group, which numbered about 300 in 2004, came from the relocated otters or from otters that survived the fur trade. Sea otters are protected in Canada as a threatened species under the federal Species at Risk Act (SARA). In April 2007, a wildlife committee changed its classification of sea otters from "threatened" to "special concern." This change reflects the continued growth of the British Columbia population and may result in fewer legal protections for the species under SARA.
In 1969 and 1970, 59 sea otters were moved from Amchitka Island to Washington state. Surveys from 2000 to 2004 counted between 504 and 743 sea otters in that area. Washington state has listed the sea otter as an endangered species since 1981.
Central and Southern California
California is the only place where the southern sea otter (Enhydra lutris nereis) lives in large numbers. In 1938, a group of about 50 of these animals was found in a remote area near Big Sur, California, by people testing a telescope. Conservation efforts, including the creation of the Monterey marine protected area by Julia Platt, Margaret Wentworth Owings, and the Friends of the Sea Otter organization, helped the population grow and spread. However, the southern sea otter population has grown more slowly than other sea otter populations and slower than nearby marine mammals like California sea lions and harbor seals. Between 1914 and 1984, the average growth rate was only 5%, and the population dropped or stayed the same in the late 1990s. The southern sea otter was listed as a threatened subspecies under the Endangered Species Act in 1977. A survey in spring 2007 counted about 3,000 sea otters in California, slightly more than recent years but much fewer than the estimated 16,000 before the fur trade. To remove the subspecies from the threatened list, the population must average at least 3,090 over three years. The Monterey Bay Aquarium’s Sea Otter Program has studied southern sea otters since 1984 to help protect them.
As the sea otter population grew, it began to conflict with shellfish fisheries. In the 1980s, the U.S. Fish and Wildlife Service tried to reduce competition between sea otters and fishermen by creating an "otter-free zone" from Point Conception to the U.S.-Mexico border. Only San Nicolas Island was allowed to have sea otters, and otters found elsewhere in the zone were supposed to be captured and moved. These plans were stopped because it was too hard to catch the many otters that swam into the zone.
In December 2014, the U.S. Fish and Wildlife Service learned that a man in Moss Landing, California, shot a mother sea otter with a pellet gun while she was nursing her twin pups.
The reasons for recent challenges facing California’s sea otters are not fully understood. Birth rates in California are similar to those in other growing sea otter populations, so the decline is likely due to high death rates. Many adult and young adult otters, especially females, have died at unusual rates. Disease is believed to be a major cause of death, and other possible causes include water pollution and drowning in fishing nets.
Although dead sea otters often sink to the ocean floor, autopsies of beached otters help scientists learn about causes of death. A study of 105 sea otters that washed ashore between 1998 and 2001 found that the main causes of death were brain infection caused by a parasite, infection from another parasite, shark attacks, and heart disease. Infectious diseases alone caused 63.8% of deaths, and most of these were caused by parasites. Infections, especially from the parasite Toxoplasma gondii, were often found in otters that died of heart disease, suggesting the infection may have caused the heart problems. T. gondii infection was also linked to shark attacks, possibly because the disease changes otter behavior, making them more likely to be attacked.
In one study, 42% of live sea otters tested had signs of infection with T. gondii, which is often deadly to sea otters. The parasite lives in the feces of wild and domestic cats. Because the parasite can enter the ocean through sewage systems, people who own cats have been encouraged to throw away cat waste in the trash instead of flushing it.
Although disease has caused many deaths among California’s sea otters, scientists do not know why the California population is more vulnerable to disease than others. Some scientists think the population’s low genetic diversity, caused by past population declines, may be a reason.
Northern California and Oregon
In the 1970s, 93 sea otters were moved to the Oregon coast. No sea otters have been seen there since the early 1980s. It is unknown whether they died or left the area.
In 2022, the U.S. Fish and Wildlife Service studied whether sea otters could be reintroduced to their historical range along the West Coast of the mainland United States. The study focused on Northern California and Oregon, where reintroducing sea otters would likely help protect the environment most. The 2022 study found that reintroducing sea otters is possible, but it did not say whether it should happen. More information and feedback from people affected would be needed before any reintroduction plan could be made. The Elakha Alliance, an Oregon nonprofit group that supports bringing sea otters back, also did its own study. This study reached similar conclusions. Both the U.S. Fish and Wildlife Service and the Elakha Alliance studies said that a detailed study of social and economic effects must be done to address concerns from the fishing industry.
Sea Otter Surrogacy
In 2002, the Monterey Bay Aquarium created the Sea Otter Surrogacy Program to help grow the number of endangered sea otters. This program helps orphaned sea otter pups survive better after they are released into the wild. It pairs a mother otter with a pup to teach the pup important skills needed to live as an otter.
When an orphaned otter pup arrives, caretakers wear black gowns and masks to hide their human appearance. This helps the pups avoid learning to trust humans, which is important for their survival in the wild. After observing the pup’s behavior, scientists choose a female otter who cannot be released back into the wild to be the pup’s surrogate mother.
The pup is slowly introduced to the mother and watched closely. When the pair shows behaviors like nuzzling, grooming, sharing food, and hugging, they are considered bonded. Once bonded, the mother teaches the pup skills needed to survive, such as finding food and grooming. Scientists focus on six key skills: (1) rolling from belly to back, (2) swimming in a specific direction, (3) trying to dive for the first time, (4) diving with only part of the body submerged, (5) diving to greater depths, and (6) finding food underwater in a holding pool.
Sea otter pups are released into the wild between 0.5 and 1.5 years old. At this age, they no longer need their surrogate mother. For two weeks after release, called the soft-release period, scientists monitor the pups using tracking devices and observations to check if they are finding food or showing signs of stress. If a pup shows stress, it is taken back, treated, and released again. Healthy pups are checked 1 to 5 times per week until they die, leave the area, the study ends, or monitoring is no longer possible.
Elkhorn Slough was chosen as the release site because it has a large otter population, plenty of resources, and is easy to access. This area, which is a place where rivers meet the ocean, is seven miles long and is home to over 100 sea otters and many other animals. The Sea Otter Surrogacy Program has helped increase the otter population in Elkhorn Slough. Scientists believe that about half of the otters living there were raised through the program, leading to a much larger otter population.