Sea Otter

Enhydra lutris
Photo: Keith Holmes, Hakai Institute

Sea otter
Enhydra lutris

Three regional subspecies:

Enhydra lutris nereis or Southern Sea Otter are the California Sea Otters that range from the Monterey Peninsula south to just north of Santa Barbara. Their limited population maintains their listing under the federal Endangered Species Act.

Enhydra lutris kenyoni or Northern Sea Otter are the sea otter in Southwest, Southcentral, and Southeast Alaska, British Columbia, and Washington State. In Alaska sea otter are protected by the federal Marine Mammal Protection Act.

Enhydra lutris lutris is the sea otter living in Asian Pacific waters from the Kuril Islands of Northern Japan to the Commander Islands off the Kamchatka Peninsula.

A Keystone Predator 

Sea otters have historically been part of the kelp forest ecology of our Northern Pacific Ocean. Prior to 1740, when the 2nd Bering expedition set out from eastern Russia to explore the Aleutian chain of islands and find America, it is estimated that around 300,000 sea otters populated their entire range skirting the North Pacific Ocean, from the very northern tip of Japan, along the Aleutian Islands down the coast of Alaska and British Columbia and continuing south through Washington, Oregon and California to Baja California in Mexico. This is not a large number of marine mammals in total, but sea otters are individually impactful—each otter contributes significantly to the ecosystem in which it inhabits. Sea otters are voracious top predators, their favorite prey are sea urchins, clams, abalone, crab and other mollusks as well as sea cucumbers. They are associated with the kelp beds they live within, keeping the urchin grazer in control so the kelp beds and the richness of life they support can thrive. They are a quintessential “keystone species,” affecting food webs beyond themselves. Like other top predators, otters provide resilience to the near shore ocean systems they live within.

Where are the Sea Otters Today?

Today sea otters inhabit the region around the Monterey Peninsula, including the Elkhorn Slough, an estuarine environment. A population of about 3,000 individuals has, despite the protection of the federal Endangered Species Act, held steady in number but has not increased its range. There are currently no sea otters moving north through bull kelp territory in Northern California or Oregon, only to be encountered again off the Washington Coast, where a healthy population resides along the northern corner of the Olympic Peninsula in Makah tribal waters. There are sea otters in parts of British Columbia, a population that is expanding into the varied coves and bays of both inland passageways and outer coast, but spots such as Gwaii Haanas National Marine Reserve are waiting for otters to re-inhabit this territory. Southeast Alaska has proved to be sea otter Shangri-la; a coastline with countless ocean bays, inlets, and islands—all replete with otter food sources—their populations have skyrocketed. Southwest Alaska also has otter readily viewed as part of the intertidal and kelp forest ecosystems. But the sea otter population in the Aleutian Islands has plummeted in recent decades. This patchwork of otter densities has had a ripple effect on the bull kelp and other kelp forest ecologies in each of these regions. Theories abound as to why the sea otters of the Aleutians have disappeared, but the effects are very clear: a stripping away of algal materials by overgrazing sea urchin. On the other hand, the success of sea otters in the Elkhorn Slough (between Santa Cruz and Monterey, California) have opened the possibility that inshore estuaries are plausible sites for reintroduction of sea otters.

Big Appetite and Lustrous Fur

Enhydra lutris, the largest member of the weasel family but the smallest marine mammal, are about 4–5 feet in length and weigh 45 (females) – 100 (largest males) pounds. They have whiskers, large webbed forepaws with retractable claws and ears and noses that can close when diving. They have great senses of sight, smell, and touch, float mostly on their back on the surface using their tail as a rudder, and have paddle-shaped hind feet for swimming, not walking or running on land. When alarmed they position themselves vertically in the water with their head periscoping around to site danger and warn their fellows. Sea otters are related to river otters, who will come down to the shore and are often mistaken for sea otters, but they are distinct species.

Sea otters dive day and night for their food and are limited in their habitat by what they can find to eat during the length of a good breath hold. For this reason they share coastal waters with the bull kelp forest that need a similar proximity to shore for best access to sunlight. Sea otters can dive and forage to about 60 feet holding their breath for about 2–4 minutes. Sea otters must eat about a quarter of their body weight each day to maintain a hypercharged metabolism, and while they eat a variety of mollusks and invertebrates, sea urchin are a favorite. An otter can eat fifteen to twenty pounds of large urchins in a day. An otter dives to the ocean floor and, using its extraordinary sense of touch, quickly identifies viable, uni-rich urchin, then carries it and a stone to the surface in a pouch of loose flesh under its forelegs. It places the stone on its belly and smashes the hard and spiny urchin to get at the nutritious food within. The otter’s capacity to hunt and eat urchins is a crucial dynamic to healthy bull kelp forest habitat, keeping urchin populations at levels that allow the bull kelp to reproduce and for delicate juvenile bull kelp to grow to maturity. 

Otters can stay completely at sea, foraging, resting, mating, giving birth and nurturing its young amongst the kelp fronds, or they can inhabit coastal estuaries, hauling out on sandbars occasionally like seals. But they get all of their freshwater needs from the prey they ingest and from seawater. Their extra-large kidneys allow them to extract freshwater from salt water.

Sea otter and pup
Sea otter and pup
Photo by Steve Choy / NOAA MBNMS

Sea otters do not have blubber like other marine mammals (think seals, whales and even dolphins) thus that extraordinary need for calories to generate heat. But they also sport the thickest fur of any animal on earth allowing them to thrive in cold Pacific waters. This dark brown lustrous pelage must be continually fluffed up so that the air bubbles trapped in between all those hairs can provide the layer of insulation they depend on. If a sea otter is not able to preen or its hairs get oily or dirty it will die quickly of hypothermia. This is why, in addition to foraging for food, a sea otter’s major preoccupation is grooming its fur. A mother will keep her pup’s fur in such a condition that it looks like a little puff ball and floats like a cork. 

Sea otters reproduction is the opposite strategy to that of the urchin and abalone, what might be called in scientific circles K-selection as opposed to r-selection. While urchin spawn millions of possible egg and sperm into the water column, otters take a more labor-intensive approach. Males will mate with a few different females, creating a harem of sorts—often leaving scars on their noses from overzealous nipping. Each female will bear just one pup, and then nurse and care for that pup for 8–12 months. She teaches her young otter baby to swim and feed and groom. She will go into estrus and get pregnant again shortly after abruptly weaning and abandoning her pup, and, gestation being six months, give birth again at any time of year. The female otter not only has her own metabolic needs but is most often gestating or nursing a baby otter, so she does not travel far, staying close to a food source that can keep her and her newborns thriving.

Sea Otters are Social Creatures 

Sea otters rest together in groups called rafts. There are rafts off the coast of Washington State that number in the hundreds of otters. Most often the females stick together, creating nurseries in the kelp beds, wrapping their pups in a kelp frond or leaving them to bob amongst the bull kelp tubes that enclose a space so they won’t float away while the mother dives for food that she will share with her baby. In this way food preferences and diving techniques are passed from one generation to the next. While females stay close to home, young males are the pioneers who venture into new territory. But these are only the few. Most otters are tightly bonded to place. They know where they are from, and if brought to some other location, as various translocation efforts have done, the otters will most often try to make a beeline back to “home,” back to where they were born. 

Raft of sea otters
Photo by Lilian Carswell, U.S. Fish and Wildlife Service

A Complicated Relationship

The sea otter’s connection to “home” along with many of its other traits make it feel like there is an intense human/otter connection. By our human standards sea otters are ridiculously adorable. Their dark brown, beady eyes in a furry face with large whiskers, often with a baby nestled cozily on their bellies, are hard not to think of as closely human. These characteristics are a way for many of us to connect emotionally to this marine mammal of our wild coastline. 

Kodiak sea otter
Kodiak sea otter
Photo by Lisa Hupp, USFWS

But the otter’s role in the kelp forest ecology, its need for the same prey we humans desire, creates a fascinating human/otter dynamic that can range from true love to raging hate. Market driven fishermen, Indigenous foragers, or recreational abalone divers tend to regard the otter as a destructive force in the nearshore waters. In some locations, the speed with which sea otters can reduce a clam population or remind abalone to stay in their cracks is astonishing. Their impact on an ecology is immense. But as Lilian Carswell, the director of the US Fish and Wildlife Service’s sea otter program, says, “The effect of otters coming back into a particular coastal ecology is enormous. We don’t necessarily know what will happen, but it will most absolutely be good for the ecology overall.” As the important role of the kelp forest has started to be recognized relative to the health of our oceans, so too have attitudes changed among fishers towards the sea otter. 

Aleutian peoples were expert hunters of the crafty sea otter. They used their baidarkas (or kayaks) with great skill, their long brimmed hats keeping waves and spray from their faces with a slight tilt of the head.

The Sea Otter Fur Trade

In 1741, as naturalist and explorer Georg Steller and the second Bering Expedition were retracing the line of the Aleutian Islands west towards home, they encountered storm after storm and were finally shipwrecked at what was later called Bering Island. Along their journey they encountered thousands of sea otters and sea cows that inhabited the kelp forests of these cold northerly Pacific waters. The sea otters were regularly killed and skinned by the Russian sailors and navy soldiers. As a shipwrecked crew, Stellar kept scurvy at bay by feeding them the plants of the island but also the meat of the plentiful sea otter. Like dogs, sea otters create their own vitamin C and though bony and tough, the sea otters kept the men of the expedition alive until they could patch their ship back together and head home to the Kamchatka Peninsula. Even then they encountered a massive storm, and all extra items were ordered to be thrown overboard. All the collections of sea otter pelts were thrown overboard as well as Stellar’s carefully preserved carcass of the now extinct sea-cow. But one navy sailor stashed his otter pelts under a bunk and arrived back onto Russian soil able to sell his furs for an astronomical sum at the Chinese border. The furs then attained the moniker “black gold” and the sea otter fur trade was initiated.

Otter pelts
Photo by Wikimedia

By 1742, the race was on to hunt or barter for as many sea otter pelts as the Russians could get. The killing was indiscriminate—males, females and pups were killed, and brutality towards Indigenous Aleut and Alutiiq people was equally harsh. Russian hunting parties moved across the Aleutians down the coast of Alaska and present day British Columbia and into California where they set up base at Fort Ross on the Sonoma Coast. Sea otters are notoriously crafty and hard to capture, so Russian, and then other western hunting expeditions, commandeered, (virtually enslaved) expert Aleuts hunters to come down the coast and do the hard work for them, stashing their kayaks (baidarkas) on deck for the long haul sailing away from their homeland. By 1840, the fur mammal populations were wiped out, and the Russians left. Soon after in 1867, they sold Alaska to the Americans. 

Farther south the Spanish controlled the otter fur trade from their base in Monterey, California and only became interested when they discovered the pelts could be traded in China for the quick-silver (mercury) they needed for their South American mining endeavors. By 1776, Bostonians and the British learned that sea otter pelts could fetch a high price in Canton, China and the rush was on again from around The Horn into the Pacific Northwest by American and British trading vessels. But the relatively small remaining population of sea otters were quickly wiped out by the mid 1800s.

In 1911 when the decimation of marine mammals was clear, an act of Congress—the North Pacific Fur Seal Treaty—made it illegal to kill sea otters as well as fur seals. But there were none to be found in any case. The last sea otter on the California coast was seen in 1917. In 1925 a wildlife refuge was established in the Aleutian Islands and a survey was done to see what wildlife was in the refuge. Not a single sea otter was found.

Otter Translocations 1960s–1970s

In fact there was a refugial population at Amchitka Island, the largest of the Rat Islands, a group of windswept treeless islands at the very lowest point of the curve of Aleutian Islands stretching between Alaska and Russia. In 1965, the first atomic test explosion was done at Amchitka Island. Another was detonated in 1969, 4,000 feet below ground. An even larger underground test, Cannikin, was planned for 1971. In the face of possible extinction of this remnant population, biologists desperately translocated otters between 1965 and 1972 to a number of mainland sites in SE Alaska, British Columbia, the outer coast of Washington State, and the Oregon coast. 

Biologists at the time knew very little about the behavior and biology of sea otters. They simply captured them, put them in cages and let them loose. It was a rather rushed and desperate attempt to spare this population of marine mammals that had already gone through the extirpation crisis of the fur trade. Many otters died of hypothermia. Unable and too stressed to groom their pellage, the matted fur no longer insulated the fat free otter, and they died easily. Each region had its chances to grow an otter population from these few animals rushed into crates, put on small planes and dropped into the sea in new territory. Oregon translocation failed completely. Southeast Alaska received otters from the Aleutians plus a few from another small otter population in Prince William Sound. It has proved to be otter nirvana and its otter population has grown steadily. Central California’s sea otters are all descendant from a single refugial raft of approximately 50 sea otter found off the Big Sur coast in 1938, a remanent population left after the fur trade.

Locations of the remnant sea otter populations

Turquoise dots indicate remnant, or refugial, sea otter populations within the United States. All sea otters in bull kelp territory today are descendant from these assorted populations that escaped the extirpation of the fur trade.