Sea otter

• 1. Introduction

  ›

  The sea otter, Enhydra lutris, carries up to 150,000 strands of fur on a single square centimetre of its body. That is the densest coat of any animal. The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adults weigh between 14 and 45 kilograms. That makes them the heaviest members of the weasel family, yet among the smallest of all marine mammals. At one time, between 150,000 and 300,000 sea otters are thought to have lived in an arc across the Pacific. This documentary asks how such a small animal stays alive in cold northern water. It asks why hunters pushed the species to the edge of extinction, and why that loss mattered to an entire underwater forest. It also asks how far the recovery has really come, and what still threatens it.

  126590

• 2. A Latecomer to the Sea

  ›

  As recently as 1982, some scientists believed the sea otter was more closely related to the earless seals than to other otters. In fact it belongs to the family Mustelidae, a diverse group that includes 14 otter species, weasels, badgers and minks. Within that family it is unusual. It makes no dens or burrows, has no functional anal scent glands, and can live its whole life without leaving the water. It is also the only living member of its genus, Enhydra.

  Genetic analysis suggests that the sea otter and its closest living relatives shared an ancestor about 5 million years ago. Those relatives include the African speckle-throated otter, the Eurasian otter, the African clawless otter and the Asian small-clawed otter. Fossils indicate that about 2 million years ago the Enhydra lineage became isolated in the North Pacific. That isolation gave rise to the now-extinct Enhydra macrodonta and to the modern Enhydra lutris. A related species, Enhydra reevei, has been described from the Pleistocene of East Anglia. The modern sea otter first evolved in northern Hokkaidō and Russia. It then spread east to the Aleutian Islands and mainland Alaska, and south down the North American coast.

  Whales and dolphins, sea cows and seals took to the water far earlier. Cetaceans entered about 50 million years ago, sirenians about 40 million, and pinnipeds about 20 million. The sea otter is a relative newcomer to marine life. Even so, in one respect it is more fully adapted to water than the seals and sea lions. Those animals must haul out on land or ice to give birth.

  The first scientific description of the animal appears in the field notes of Georg Steller, dated 1751. Carl Linnaeus then described the species in the 1758 tenth edition of his landmark Systema Naturae, calling it Lutra marina. After numerous name changes, the name Enhydra lutris was accepted in 1922. The animal was also sometimes called the sea beaver.

  Three subspecies are recognized. The Asian sea otter, Enhydra lutris lutris, lives around Russia's Kuril Islands and the Commander Islands, and it is the largest. The northern sea otter, E. l. kenyoni, ranges from Alaska's Aleutian Islands to Oregon. The southern sea otter, E. l. nereis, is native to central and southern California.

  The full genome of the northern sea otter was sequenced in 2017. Genetic evidence shows that the species suffered earlier population crashes, about 9,000 to 10,000 generations ago and again 300 to 700 generations ago. Both came long before the fur trade, and disease was the likely cause. Estimates suggest each crash left only ten to forty animals for roughly eight to forty-four years. Those older scars left the species with little genetic diversity, which would make later losses far more dangerous.

  89111517

• 3. Warm Without Blubber

  ›

  Between the fur of a sea otter and its skin lies a layer of air that the animal's own body heats. This is how the sea otter stays warm, because unlike most marine mammals it has no blubber. The coat has long, waterproof guard hairs over short underfur, and the guard hairs keep the underfur dry. Cold water never reaches the skin, so heat loss stays low. The design has a weakness. As the otter dives, the air layer compresses, and the fur insulates less well just when the animal is foraging.

  Keeping that coat working takes constant effort. The guard hairs repel water only when they are perfectly clean. So the sea otter grooms every part of its body, helped by loose skin and an unusually supple skeleton. It cleans the fur, untangles knots, removes loose fur, rubs out water, and blows air back in. To a casual observer it looks like scratching, yet the animals are not known to have lice or other parasites. The fur is shed and replaced gradually, so it stays thick all year with no distinct molting season. Its colour is usually deep brown with silver-gray speckles, though it ranges from yellowish brown to almost black.

  Male sea otters usually weigh 22 to 45 kilograms and measure 1.2 to 1.5 metres, and one specimen reached 54 kilograms. Females weigh 14 to 33 kilograms and measure 1.0 to 1.4 metres. Weight also tracks crowding. In densely populated areas, males average 28.3 kilograms and females 21.1. In sparser populations, males average 39.3 and females 25.2. Presumably thinly spread otters can monopolize more of the food.

  The nostrils and small ears of a sea otter can close, and its hind feet are long, broadly flattened and fully webbed. Those hind feet provide most of its propulsion. The fifth digit on each hind foot is the longest, which helps when swimming on the back but makes walking difficult. The front paws are short, with retractable claws and tough palm pads that grip slippery prey. Dense, heavy bones reduce buoyancy. Even so, the otter floats easily, because its lungs hold about 2.5 times as much air as those of similar-sized land mammals.

  Underwater, the otter moves by flexing its rear end up and down, and it can reach 9 kilometres per hour. At the surface it floats on its back and sculls with its feet and tail. At rest it folds all four limbs onto its torso to save heat. On particularly hot days it may hold the hind feet underwater to cool. On land it walks with a clumsy, rolling gait and can run in a bounding motion.

  In dark or murky water, long, sensitive whiskers and front paws help the otter find prey by touch. Researchers who approach in plain view see sea otters react faster when the wind blows toward the animals. That suggests smell is a more important warning sense than sight. Sight works above and below water but is not as good as a seal's. An adult's 32 teeth, especially the molars, are flattened and rounded for crushing rather than cutting. Seals and sea otters are the only carnivores with two pairs of lower incisors instead of three. Teeth and bones are sometimes stained purple from eating sea urchins.

  The price of living in cold water is a furious metabolism. A sea otter's metabolic rate is two or three times that of a land mammal of similar size. It must eat an estimated 25-38% of its own body weight each day. Digestive efficiency is estimated at 80-85%, and food can pass through in as little as three hours. Most of its water comes from food, but unlike most marine mammals it also drinks seawater. Its relatively large kidneys let it make fresh water from the sea.

  The coat may be only a stopgap. Having returned to the sea about 3 million years ago, the sea otter may be caught at the earliest point of a shift from fur to blubber. As dives grow longer and deeper, the air layer holds heat and buoyancy less well, while blubber stays efficient and can even fuel deep dives.

  2637395253

• 4. Tools and Appetite

  ›

  A sea otter can hold its breath for up to five minutes, but its dives typically last about one minute and never more than four. It is the only marine animal able to lift and turn over rocks, which it often does with its front paws while searching for prey. It also plucks snails from kelp and digs deep into mud for clams. It is the only marine mammal that catches fish with its forepaws rather than its teeth. Under each foreleg it has a loose pouch of skin that stretches across the chest. In this pouch, preferably the left one, it stores food for the trip to the surface, and sometimes a rock.

  At the surface the otter eats while floating on its back, tearing food apart with its forepaws. It can chew and swallow small mussels shell and all, while large mussel shells may be twisted apart. It uses its lower incisors to reach the meat in shellfish. Large sea urchins are mostly covered in spines. So the otter bites through the underside, where the spines are shortest, and licks out the soft contents. While eating, it rolls in the water often, apparently to wash scraps from its fur.

  The rock in the pouch is the reason the sea otter is counted among the few mammals that use tools. To open hard shells, it may pound its prey with both paws against a rock resting on its chest. To pry an abalone off the sea floor, it hammers the shell with a large stone. Observers have counted 45 blows in 15 seconds. An abalone can cling to rock with a force equal to 4,000 times its own body weight, so releasing one takes several dives.

  The sea otter is an apex predator that eats over 100 prey species. In most of its range, its diet is almost entirely marine invertebrates such as sea urchins, sea stars, sea cucumbers, fat innkeeper worms, crustaceans, chitons, abalones, limpets, clams, mussels and scallops. Prey ranges from tiny limpets and crabs to giant octopuses. When prey comes in several sizes, otters pick the larger ones. In California they have been noted to ignore Pismo clams smaller than 3 inches across. Contrary to popular depictions, sea otters rarely eat starfish, and any kelp they swallow passes through undigested. They occasionally take seabirds, and in California the most commonly eaten were western grebes.

  Fish matter more in some northern waters. In studies at Amchitka Island in the 1960s, where the otter population was at carrying capacity, 50% of the food in sea otter stomachs was fish. Those fish were usually bottom-dwelling and sedentary or sluggish. South of Alaska on the North American coast, fish are a negligible part of the diet.

  Individuals within an area often differ in foraging methods and prey, and they tend to follow the patterns of their mothers. A 2007 Californian study found a surprise. Where food was scarce, the population ate a wider variety of prey, yet the diets of individual otters were more specialized. Foraging takes between 24% and 60% of an otter's day, depending on food supply. The first session starts about an hour before sunrise, and a third may occur around midnight. Otters can thoroughly strip an area of abalone except for those in deep rock crevices. They never wipe out a prey species completely.

  3044454672

• 5. Rafts and Pups

  ›

  A raft of sea otters typically holds 10 to 100 animals, and the largest ever seen contained over 2000. Adults and independent juveniles forage alone, but they rest together in single-sex groups, and male rafts are larger than female ones. To avoid drifting out to sea while resting and eating, otters may wrap themselves in kelp.

  Autumn is the peak breeding season in most areas, and a male is most likely to mate if he holds a territory in a place that females favor. Males defend territory from spring to autumn. They patrol the boundaries to keep other males out, although actual fighting is rare. Adult females move freely between territories and outnumber the males there by an average of five to one. Males without territories gather in large male-only groups and swim through female areas looking for a mate. A pair bonds for the 3 days of estrus. During mating the male holds the female's head or nose in his jaws. Visible scars are common, and in severe cases trauma to the face or nose can kill the female.

  The species has a range of voices. A pup's cry is often compared to that of a gull. Females coo when apparently content, while males may grunt. Frightened adults may whistle, hiss, or in extreme circumstances scream. Captive otters have shown sibling-like bonds. At the Shedd Aquarium, the younger Cayucos followed the older Kiana around and copied her play with toys. At the Osaka Aquarium Kaiyukan, a female named Pata kept stealing food from another female, Ellen, to present it to a male named Kutan as a gift. In the 1930s in Russia, a captured otter with an ingrained fear of humans dragged its enclosure mate into the water whenever a person appeared.

  Researchers long assumed that rafts were randomly assembled crowds. According to UC Santa Cruz professor Tim Tinker, preliminary analysis of tagged otters in Monterey Bay shows distinct clusters inside the large groups. Mated pairs and females with synchronized breeding also stay together over many years. Sea otters pass knowledge from mother to pup and sideways within groups. Whether that adds up to a full culture remains unknown.

  Births happen year-round, with peaks between May and June in northern populations and between January and March in southern ones. Birth usually takes place in the water and typically produces a single pup. Twins occur in 2% of births, but usually only one pup survives. Gestation appears to vary from four to twelve months, because the species can delay implantation and then be pregnant for four months. In California, females breed about twice as often as those in Alaska.

  A newborn has open eyes, ten visible teeth and a thick coat of baby fur. Its mother may lick and fluff it for hours. Afterward the pup's fur holds so much air that it floats like a cork and cannot dive. The baby fur is replaced by adult fur after about 13 weeks. Nursing lasts six to eight months in Californian populations and four to twelve months in Alaska, and the mother starts offering bits of prey at one to two months. The pup then practices swimming and diving for several weeks before it can reach the sea floor. At first it brings up things of little food value, such as brightly colored starfish and pebbles.

  By one estimate, only 25% of pups survive their first year, and pups of experienced mothers fare best. Females do all the feeding and raising, and have occasionally been seen caring for orphans. A mother cradles her pup on her chest and grooms it constantly. When she dives, she leaves it floating, sometimes wrapped in kelp, and it cries loudly until she returns. Mothers have been known to carry their pups for days after the pups' deaths.

  Females reach sexual maturity at around three or four years old and males at around five. In the wild, sea otters live up to 23 years, with males typically living 10 to 15 years and females 15 to 20. The Seattle Aquarium was home to the oldest recorded female, Etika, who lived to 28, and the oldest recorded male, Adaa, who reached 22 years and 8 months. Wild otters often develop worn teeth, which may explain their shorter lives.

  7357686970

• 6. Keystone of the Kelp

  ›

  Sea urchins graze the lower stems of kelp, and when the stems break, the kelp drifts away and dies. North Pacific areas without sea otters often turn into urchin barrens, with abundant urchins and no kelp forest. Sea otters keep urchin numbers in check, which is why they are a classic keystone species. Their effect on the ecosystem is far larger than their size or numbers would suggest. Kelp forests are extremely productive, and they absorb material from the atmosphere through photosynthesis. Sea otters may therefore help mitigate the effects of climate change.

  The evidence is strongest where otters returned. Reintroduction to British Columbia led to a dramatic improvement in coastal ecosystem health. Similar changes followed recoveries in the Aleutian and Commander Islands and along the Big Sur coast of California. The picture is not uniform, though. Some California kelp forests have thrived without sea otters, with urchins apparently held down by other factors. The otter's role also seems more important on open coasts than in sheltered bays and estuaries.

  In mussel beds on rocky shores, otters pull mussels off the rock. That frees space for competing species and raises diversity. Recent studies trace further benefits to them. When otters dig for prey, they stimulate seagrass growth and boost the genetic diversity of eelgrass meadows. That makes the meadows more resilient and helps protect coastlines from storm surges and rising seas. By controlling crab populations, otters also hold coastal erosion to natural levels. They keep down destructive invaders such as the European green crab, which the American government has spent millions of dollars trying to eradicate with little success. In the Bering Sea, Enhydra lutris controls the red king crab, which is out of control in the Barents Sea.

  Some of those benefits reach human pockets. Kelp is used in diverse food and pharmaceutical products. Human divers harvest red sea urchins to protect the kelp, but otters hunt more urchin species and control them more consistently. A healthy kelp forest also nurtures fish, including commercially important species. Sea otter tourism was projected to be worth about CA $41.5 million per year, or US $30.5 million, in one study. On Vancouver Island, otters ranked as the second most popular wildlife-tour attraction, only slightly behind whale watching. In California, households were consistently willing to pay more to see otters, and even more simply to know they were there.

  Abalone, clams and crabs are also food for people, and that sets up a bitter dispute. Sea otter predation can deplete a fishery until it is no longer commercially viable, and scientists agree that otters and abalone fisheries cannot share an area. Yet otters have sometimes been blamed for shellfish declines more likely caused by overfishing, disease, pollution and seismic activity. Shellfish have also declined in places with no otters. Conservationists note that the rich shellfish beds along the coast are a recent result of the fur trade nearly wiping out the otter. In southern California, commercial abalone fishing ended from overfishing in 1997. Even more telling, white abalone, which never overlapped with sea otters, had fallen 99% by 1996 and became the first marine invertebrate federally listed as endangered.

  47464633

• 7. Soft Gold

  ›

  For thousands of years, archaeological evidence shows, indigenous peoples hunted sea otters for food and fur. Many maritime cultures of the North Pacific also saw the animal as kin to humans. These included the Ainu of the Kuril Islands, the Koryaks and Itelmen of Kamchatka, the Aleut, and the Haida of Haida Gwaii. The Nuu-chah-nulth, Haida and other First Nations of coastal British Columbia made chiefs' regalia from the pelts. Pelts were given in potlatches to mark coming-of-age ceremonies, weddings and funerals. The Aleuts carved otter bones into ornaments and game pieces, and used powdered baculum as a fever medicine. In Ainu folklore, the sea otter sometimes carries messages between humans and the creator, and the epic Kutune Shirka tells of wars fought over a golden sea otter. A widespread Aleut legend says lovers or despairing women plunged into the sea and became otters.

  The Maritime Fur Trade changed everything, and it would eventually kill approximately one million sea otters. In the early 18th century, Russians began hunting otters in the Kuril Islands and selling the pelts to the Chinese at Kyakhta. In 1741, on his second North Pacific voyage, Vitus Bering was shipwrecked off Bering Island in the Commander Islands. He and many of his crew died there. The survivors, including the naturalist Georg Steller, found sea otters on the beaches. They spent the winter hunting otters and gambling with the pelts. They returned to Siberia having killed nearly 1,000 otters, and sold the pelts at high prices. Even so, at Kyakhta prices the pelts would have paid for only one tenth of the cost of Bering's expedition.

  Thus began what is sometimes called the Great Hunt, which continued for another hundred years. The Russians found sea otters far more valuable than the sable skins that had driven their expansion across Siberia. By 1745, hunters had depleted the Commander Islands and moved on to the Aleutians. They first traded with the Aleuts. Later they enslaved them, taking women and children hostage and torturing and killing Aleut men to force them to hunt. By the Russians' own estimate, the Aleut population fell from 20,000 to 2,000. By the 1760s the Russians had reached Alaska. In 1799, Tsar Paul I merged the rival fur companies into the Russian-American Company, with an imperial charter and a monopoly on trade rights and territorial acquisition. Under Aleksander I, naval officers sent alarming reports of abuse of native peoples, and administration of the company passed to the Imperial Navy. In 1818, the indigenous peoples of Alaska were granted civil rights equivalent to townsman status in the Russian Empire.

  Others joined in farther south. Spanish explorers bought pelts from Native Americans along the coasts of what is now Mexico and California and sold them in Asia. In 1778, British explorer Captain James Cook reached Vancouver Island and bought furs from the First Nations people. When his ship stopped at a Chinese port, the pelts sold rapidly at high prices and became known as "soft gold". Traders then arrived from all over Europe and North America. Between 1803 and 1846-72 American ships took part in the California hunt, harvesting an estimated 40,000 skins and tails. Only 13 Russian-American Company ships took part, and they reported 5,696 skins taken between 1806 and 1846. In 1812, the Russians founded Fort Ross in northern California as their southern headquarters.

  San Francisco Bay shows how fast it could go. In 1812, the Fort Ross founder Ivan Kuskov found otters scarce at Bodega Bay and sent a party of Aleuts into the bay. Within three months they caught 1,160 sea otters. By 1817 the otters of the area were practically eliminated. Elsewhere, the Russian-American Company ended hunting in the Aleutian Islands by 1808 as a conservation measure, and ordered further restrictions in 1834.

  When Russia sold Alaska to the United States in 1867, the Alaska population had recovered to over 100,000. Americans resumed hunting and quickly wiped out the otters again. As the animal grew rare, prices climbed. A pelt brought $105 to $165 in the London market during the 1880s, but by 1903 one could be worth as much as $1,125. In 1911, Russia, Japan, Great Britain on behalf of Canada, and the United States signed the Treaty for the Preservation and Protection of Fur Seals, which imposed a moratorium on harvesting sea otters. So few remained, perhaps only 1,000-2,000 in the wild, that many believed the species would go extinct. Another animal had already been lost. The overhunting of sea otters near the Commander Islands likely contributed to the extinction of the Steller's sea cow.

  27904151

• 8. The Long Recovery

  ›

  Today the sea otter occupies about two-thirds of its former range, a rebound counted among the great successes of marine conservation. The fur trade had left an estimated 1,000 to 2,000 animals in 13 colonies. Estimates made between 2004 and 2007 gave a worldwide total of about 107,000. Steep declines found since then in Alaska and Russia cast doubt on that figure, and the IUCN still lists the species as endangered. Hunting is no longer legal except for limited harvests by indigenous peoples in the United States. The Marine Mammal Protection Act of the 1970s made hunting there highly illegal.

  British Columbia shows both the failure of paper protection and the power of moving animals. A remnant population survived off Vancouver Island into the 20th century. It died out despite the 1911 treaty, and the last sea otter was taken near Kyuquot in 1929. From 1969 to 1972-89 otters were flown or shipped from Alaska to the island's west coast. By 2013 that group had grown to over 5,600, at an estimated 7.2% a year. In 1989, a separate colony was found on the central coast. Nobody knows whether transplants founded it or whether it was a remnant that went unnoticed. It numbered about 300 in 2004 and exceeded 1,100 in 2013. In 2007 Canada set the species' status at "special concern".

  Washington's story began with 59 otters moved from Amchitka Island in 1969 and 1970 and released near La Push and Point Grenville. The group dipped to somewhere between 10 and 43 animals before climbing to 208 in 1989. By 2017 it exceeded 2,000. Oregon was less lucky. The last native otter there was probably shot in 1906, and 95 otters transplanted from Amchitka in 1970 and 1971 soon disappeared again. A male settled at Simpson Reef off Cape Arago for six months in 2004. On the 18th of February 2009, another male was spotted at Depoe Bay.

  California's otters descend from a single colony of about 50 animals near Bixby Creek Bridge in March 1938. The historic population had been about 16,000. In the late 1980s, the U.S. Fish and Wildlife Service moved about 140 southern sea otters to San Nicolas Island as insurance against an oil spill on the mainland. To the surprise of biologists, most swam back. A group of twenty swam 74 miles north to San Miguel Island. By 2005 only 30 remained at San Nicolas, but the count reached 104 in spring 2016. In 1986 the agency had also declared an "otter-free zone" from Point Conception to the Mexican border. The plan failed, and on the 19th of December 2012 the agency declared the experiment a failure.

  The California count has swung hard. For southern sea otters to be considered for removal from the threatened list, the population had to exceed 3,090 for three consecutive years. The three-year average reached 3,272 in 2016, the first time it passed that threshold. Then the spring 2017 survey fell from 3,615 to 2,688, a loss of 25%. Shark bites are one factor. Great white sharks do not eat otters, apparently mistaking them for seals, yet bitten carcasses rose from 8% in the 1980s to 15% in the 1990s and 30% in 2010 and 2011. The parasite Toxoplasma gondii, carried by cats and flushed into the ocean through sewage, is another major cause of death. A toxin called microcystin, which builds up in shellfish, has also poisoned otters.

  Alaska holds the heart of the range, and it has lost the most. The population there was estimated at 100,000-125,000 in 1973 and 73,000 by 2006. In the Aleutian Islands alone, the count fell from an estimated 55,000-100,000 in the 1980s to around 6,000 by 2000. The most widely accepted hypothesis is that killer whales ate them, but there is no direct evidence of orcas preying on otters to any significant extent. In Prince William Sound, the Exxon Valdez oil spill of the 24th of March 1989 killed thousands of otters. Oil ruins the fur's ability to hold air, and the animals can die quickly from hypothermia. A U.S. Fish and Wildlife Service spokesperson wrote that the sea otter had become "a playful, photogenic, innocent bystander" in the public mind, and cast as the victim.

  Habitat protection helps. An estimated 1,200 sea otters live in the Monterey Bay National Marine Sanctuary, and more than 500 in the Olympic Coast National Marine Sanctuary. Captive breeding programs at the Monterey Bay Aquarium and The Marine Mammal Center may help restore genetic diversity.

  Russia and Japan show how fragile the gains are. Before the Great Hunt, around 20,000 to 25,000 otters lived near the Kuril Islands, and the hunt left only 750 in the Russian region. By 2004 the Russian total had climbed to about 27,000. Surveys from 2019 to 2024 found only about 3,000 around the Kurils, 1,673 around the Commander Islands and 1,565 around Kamchatka. Illegal poaching is believed to contribute. Japan's only confirmed population lives off eastern Hokkaido, where the last count found about 50 otters. The small Etopirika Foundation, run by Yoshihiro Kataoka, monitors them. In April 2025, Kataoka documented the first lethal case of avian influenza among sea otters.

  1414513