- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Carnivora
- Family: Mustelidae
- Genus: Enhydra
- Species: lutris
- Average Male Length: 5 ft (1.5 m)
- Average Female Length: 4 ft (1.25 m)
- Average Male Weight: 65 lbs (30 kg)
- Average Female Weight: 60 lbs (29.5 kg)
- Average Lifespan: 10-12 years
The only aquatic member of the weasel family, the playful sea otters live off the kelp coasts of the Pacific Ocean in North America and Asia. Their historic range stretches from Japan, along the coast of Siberia and Aleutian Chain to Alaska, and down to Baja California. Currently, sea otters can be found in Canada, Russia, Japan, California, and Washington. But, the majority of all wild sea otters are found in Alaskan waters. Recent reports of sea otter sightings have also occurred in Mexico.
Kelp canopies are an important habitat component, used for foraging and resting. It is used for protection from severe ocean winds. Though also strongly associated with rocky substrates, sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt.
Though there are several subspecies, in the U.S., there are two distinct sea otter subspecies: the Northern sea otter (Enhydra lutris kenyoni) and the Southern sea otter (Enhydra lutris nereis). Northern sea otters can be found along Aleutian Islands, Southern Alaska, British Columbia, and Washington. Southern sea otters, also known as California sea otters, live in the waters along the California coastline.
Sea otter fur ranges from brown to almost black. Their guard hairs, long coarse hairs forming a protective coating over the undercoat of mammal, are typically silver or light brown. As the individual ages, its head and neck will lighten until white.
They have a highly buoyant, elongated body, blunt snout and small, wide head. They have an acute sense of smell and taste, excellent vision both above and below the water surface, and heavily rely on their sense of touch. Their sense of hearing is not yet fully understood, although studies suggest that sea otters are sensitive to high-frequency sounds.
Other features include small eyes, visible ears, and retractable claws on its front paws to grab prey and to groom. Long whiskers to help them detect vibrations in murky waters. Its long, flattened tail is used as a rudder for steering and for added propulsion.
Sea otters, as marine mammals, have most of the classic features needed to survive in the cold waters of the Pacific Ocean. They have webbed and flipper-like hind feet, water-repellent fur to keep them dry and warm, and nostrils and ears that close in the water. Their teeth is unique for a mammal. Rather than sharp teeth for tearing, a sea otter’s blunt teeth are designed for crushing shells.
With the exception of its nose and paw pads, the sea otter’s body is covered in dense fur. Considered the finest amongst all mammals, the short, brown underfur can be as dense as one million hairs per square inch, making it also the densest. The top layer of waterproof guard hairs keeps the skin dry while the underfur layer keeps the body insulated. The sea otter depends on its dense coat to keep it warm in the cold, coastal Pacific because, unlike other marine mammals, it does not have any blubber.
It is critical for a sea otter to always be meticulously clean. After eating, it will wash itself in the ocean using its teeth and paws. For if the fur becomes soiled, it will not be able to remain waterproof and insulated.
A sea otter’s diet is almost exclusively marine invertebrates. They are known to munch on about 40 marine species, including abalone, mussels, clams, crabs, snails, urchins, and fish, depending on what is available in its habitat. They are also known to eat squid, octopus, scallops, and sea stars.
Feeding is a very important activity, mainly occurring in the morning and afternoon. Sea otters eat approximately 25% to 30% of their weight in food each day to support their high metabolism. To capture their food, they must to dive, sometimes up to 250 feet.
As a marine mammal, the sea otter will spend most of its time in the water. In some locations, it will come ashore to sleep or rest. But, they will typically rest, floating on their backs, in coastal kelp forests, often draping the kelp over their bodies to keep from drifting away.
They are equally active both night and day. Foraging bouts last few hours, starting just before sunrise. A second foraging bout begins in the afternoon, lasting until sunset. A third foraging session may also occur around midnight. In between foraging, sea otters will groom each other and rest.
It is one of the few mammals other than primates known to use tools. They are often seen with a rock to hammer open a clam, mussel, or shellfish. Otters will place the rock on their chests while repeatedly smash the shellfish against it until it breaks open for a tasty meal.
Sea otters are social animals, floating together in groups called rafts of less than 10 to more than 100. Usually, these groups are separated by sex with females and pups spending time in one group with males in another.
Males will patrol territorial boundaries and attempt to exclude other adult males from the area. Females are allowed to move freely between and among male territories. Despite this, they are weakly territorial; fighting and aggression are a rare occurrence.
Sexual maturity occurs around the age five or six for males, but do not become territorial or reproductively successful for the next two or three subsequent years. Most female sea otters are sexually mature at age four or five, though some are mature as early as 2.5 years.
Sea otters are considered polygynous, although the exact nature of the mating system may vary. There is no define mating season as it occurs throughout the year. After a gestation period of six to eight months, females will give to a single pup. Twinning has been documented, but rare; and when they do occur, neither pup is likely to survive.
Pups will stay with their mothers for the first eight months of their life. They are often wrapped in kelp, bobbing on the surface of the ocean like a cork, when the mother leaves to hunt. Mothers will spend majority of their time grooming the pups and carrying them on their chests until they learn to swim at around four weeks of age.
Although difficult to hear from shore, sea otters exhibit a variety of vocal behaviors, with pups being the most vocal. A pup can be heard squealing when its mother leaves and when a male approaches. Their calls has been described to that of a gull’s. Other vocalizations include coos and grunts (when eating or courtship), whines (when frustrated), and growls, snarls, whistles, and hisses (when frightened or distressed).
Conservation and Threats
Historically, sea otters have numbered between several hundred thousand to more than a million. Since the 1700s, native peoples throughout the otter’s range sustainably harvested sea otters for their pelts. But due to an intensive commercial fur trade from 1740 to 1900, worldwide numbers plummeted down to a total of one to two thousand in the early 1900s. Numbers dropped so low that commercial harvesting was forced to cease.
The species was protected by the International Fur Seal Treaty in 1911. At the time only 13 remnant colonies remained. Remnant populations were located in the Kuril Islands, Kamchatka, and in the Commander Islands of Russia, five in southwestern Alaska (Aleutian Islands, Alaska Peninsula, and Kodiak Islands), one in southcentral Alaska (Prince William Sound), Canada (Queen Charlotte Islands), central California, and Mexico (San Benito Islands). However, the Queen Charlotte, Canada, and San Benito Island subpopulations have presumably died out.
Since the 1980s, the species had been recovering in many areas throughout their range thanks to intensive management and regulatory efforts by several governments. There is an estimate of 106,000 worldwide, with just over 3,000 in California.
But contemporary issues such as oil spills, potential fisheries interactions, predation, and disease have prevented populations from thriving or have caused population declines throughout much of the species range. Both subspecies in the United States are listed as threatened under the Marine Mammal Protection Act and in Canada, the species is protected under the Species at Risk Act. It is also listed in IUCN as an endangered species and under CITES Appendix I.
Human activities, especially coastal development and marine pollution, is an immense threat to species. In 1989, hundreds, if not thousands, of sea otters were killed as a direct result of the Exxon Valdez oil spills in Prince William Sound in Alaska.
California sea otter is particularly vulnerable to oil contamination due to its low numbers and because they are located in a small geographic area compared to other sea otter populations.
When sea otters come into contact with oil, it causes their fur to mat, preventing proper insulation. Without their natural protection from the frigid water, sea otters can quickly die from hypothermia, with no blubber layer to rely on.
The toxicity of oil is harmful to sea otters, causing liver and kidney failure as well as severe damage to their lungs and eyes.
Another major threat is the pollution running off into the ocean, contaminating the sea otters’ habitat. This can jeopardize their food sources, as well as harm them directly. Sea otters are often contaminated with toxic pollutants and disease-causing parasites as a result of runoff in coastal waters. In California, parasites and infectious disease cause more than 40% of sea otter deaths. Hundreds of sea otters have succumbed to the parasites Toxoplasma gondii and Sacrocystis neurona. Scientists have also reported the accumulation of man-made chemicals, such as PCBs and PBDEs, at some of the highest levels ever seen in marine mammals.
Additional threats include entanglement in fishing gear, particularly gill nets, boat strikes, toxins, and competition with commercial fisheries for food.
- It is the heaviest member of the weasel family.
- As a keystone species of a predator, sea otters are critical to maintaining the balance of near-shore kelp ecosystems. It keeps the population down of those who feed on the kelp forests. It also indirectly help reduce atmospheric carbon dioxide levels, as the kelp forests play an important role in capturing carbon in coastal ecosystems.
- It is the second smallest marine mammal.
- The oldest sea otter that has lived was 25.
- At birth, sea otters weigh approximately 5 lbs and 10 inches.
- They are the only otter species to give birth in the water.
- When sea otters are searching for food, they store what they have found in the loose skin folds at their armpits.
- Sea otter pup’s fur traps so much air that they actually cannot dive underwater.
References + For More Reading
Read the Last Animal Spotlight: Resplendent Quetzals