Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Conservation Status: Threatened - Protected
Southern Sea Otter
(Enhydra lutris neres)Mammals • Marine
Sea otters, the smallest and most recently evolved of all marine mammals, are in the family Mustelidae that includes weasels, ferrets, badgers, skunks, freshwater and sea otters, and minks. There are three subspecies: the northern (Alaska) sea otter Enhydralutris kenyoni; the Asian sea otter E. l. lutris; and the southern sea otter E. l. neresis. The genus name, Enhydra, comes from the Greek for “in water”; the species name, lutris , from the Latin word for otters; and the subspecies name of the southern sea otter, neresis, means sea nymph or swimmer.
At the Aquarium
Our four sea otters, Charlie, Brooke, Maggie, and Gidget, were found stranded on the beach when only a few days old; in fact, Charlie still had his umbilical cord attached. After rehabilitation at a marine mammal care center, it was determined that they could not survive in the wild and except for Maggie, they came to the aquarium at an early age. Maggie came to the Aquarium from another facility in 2010 when she was nine years old. Charlie and Brooke arrived in 1998 before we opened. Charlie sucks his paw as he sleeps. Brooke likes to hide toys in her “pocket”. Maggie has become very attached to young Gidgit. Watch for them swimming side-by-side.
Distribution is dependent on the geographic location of the subspecies. southern sea otter: along the coast of northern California just south of San Francisco to Santa Barbara County in central California; northern sea otter:Asian sea otter: Kuril Islands and along the eastern coast of the Kamchatka Peninsula
These coastal animals spend almost their entire life at sea and most of the time on the water’s surface. They typically stay within 1-2 km (0.6-1.2 mi) from shore in primarily shallow waters that are protected from coastal winds, have rocky bottoms, and are 15-23 m (50-75 ft) deep. They usually have a coastal home range of 8-16-km (5-10 mi).
Reproductive females and territorial males are mostly found in kelp-dominated regions while juveniles and non-territorial males occupy sandy habitats. They occasionally haul out onto land to rest. In kelp they are camouflaged; find food; can wrap themselves in the kelp to remain stationary; and find protection from strong winds and waves.
Recent research using tracking with GIS supplemented by historic data sets has indicated that the foraging and migratory ranges for southern sea otters are about 603 km (375 mi) from the Gaviota coast in Santa Barbara County to Half Moon Bay in San Mateo County. Males mostly occupy and forage in the waters of the southern and northern boundaries and females and their offspring in the central coastal range.
Most otters live within two-thirds of a mile of shore in coastline waters that are protected from coastal winds, with rocky bottoms at depths of 15-23 m (50-75 ft). Some are found along sandy shores. They occasionally haul out onto land to rest. Kelp, used for both foraging and resting, is an important part of a southern sea otter’s habitat.
Sea otters have a narrow skull with a wide rostrum and long nasal bones. They have pronounced canine teeth. Their facial vibrissae (whiskers) may reach 10.2 cm (4 in) in length but are usually worn down to about 5 cm (2 in). Their dexterous front paws have retractile claws while the claws on their flat, webbed hind feet that act as flippers do not retract. They have a flat, blunt tail that can be about one-fourth their total body length.
An otter’s dense fur can be brown, black, blonde, and even silver in coloration and facial hair may turn white with age.
They are sexually dimorphic. The smaller adult females weigh 16-29.5 kg (35-65 lb) and males, 27-40.9 kg (60-90 lb). Body length, (not including the tail), is typically from 91 to 122 cm (3 to 4 ft).
Diet and Feeding
Sea otters have a high metabolism and need to eat large amounts of food in order to keep warm in their cold water habitat. In the ocean, sea otters eat 25-30% of their body weight each day.
The diet preferences of otters varies but most sea otters eat only two or three types of food. Food preferences are learned from their mothers. Otters mostly feed on invertebrates such as sea urchins, squid, octopus, crabs, mussels, abalone and other mollusks usually in waters less than 25 m (82.5 ft) deep. To maintain their metabolism, they eat up to one third (25-30%) of their body weight per day. Otters mostly feed on invertebrates such as sea urchins, squid, octopus, crabs, mussels, abalone and other mollusks usually in waters less than 25 m (82.5 ft) deep. Sometimes they eat birds. To maintain their metabolism, they eat up to one third (25-30%) of their body weight per day. Female otters frequently pass on their preference for certain food items to their offspring.
Females become sexually mature at 3-4 years of age and males at 4-5. They breed in the water throughout the year. Mating may appear violent when the male will grab the female from behind, clamp his jaws on her head, neck, or nose and upper jaw. The pair thrashes and rolls with the females head under water most of the time. Mating can last up to 20 minutes.
Females give birth about every other year. Gestation is approximately 6-9 months, depending on the time of implantation of the egg in the uterus. Pups are born in the water and weigh 1.4-2.3 kg (3-5 lb) at birth. They are covered with shaggy yellowish to light brownish colored fur, called lanugo. Their eyes are open. They have the ability to float but cannot dive because of their buoyancy. A pup is very dependent on its mother. She nurses and grooms the pup while she swims on her back and supports the pup on her chest. The pup is nursed for 2-3 months on milk containing 20-25 percent fat and starts to eat bits of solid food at about 6-8 weeks and then fed bits solid food. While the female hunts for food she may often place the pup on top of kelp, wrapped in strands around the pup to keep it from drifting.
At six months of age, sea otters are able to care for themselves. Young males leave to find a bachelor group while females will remain in the area in which they were raised.
Extensive observations made by researchers at USGS’s Western Ecological Research Center have shown that, depending on population status and food availability, southern sea otters usually spend 40-50 percent of the time resting, about 10 percent grooming, 2-20 percent interacting, 1-5 percent traveling, and 20-40 percent feeding.
Southern sea otters are well adapted for life in the water but they walk slowly and are quite awkward on land. They often lie on their backs and move by paddling their hind legs, traveling only about 1.6 km (1 mile) an hour. While swimming underwater, they close their ears and tuck their front limbs tight to their bodies and move using their hind limbs and tail in an up-and-down motion. They dive to 36.6 m (120 ft) below the surface, usually in search of food. Dives usually last under a minute, but can last up to four minutes. They feed and groom for most of the day, taking a 2-4 hour rest in the middle of the day. They usually sleep or rest through the night on their backs in the water. When resting, sea otters sometimes tie themselves with kelp fronds to keep from drifting.
Sea otters are social animals that live in groups of 12-100+ called rafts. These rafts are made up of either males or females and their young. Otters may play with one another, rarely fight, and usually ignore other marine mammal species.
Lacking blubber, sea otters rely on dense, fine, short insulating underfur and coarse outer guard hairs to aid in heat conservation and to keep warm. Because their fur is crucial to their health and survival, a sea otter has to spend a portion of its day grooming. Using its sharp claws as a comb, the otter scratches and brushes its fur to untangle and clean it. Its loosely jointed skeleton allows it to twist, roll, and squirm to reach every part of its fur, even that on its back. It also has the advantage of a coat that is so loose; it can be pulled around to clean areas that are hard to reach. In this grooming process a layer of insulating air bubbles is trapped between the otter’s warm skin and the cold water. This shield of trapped air is the otter’s primary defense against heat loss. The otter rubs hard with its paws to trap the air next to its skin. It may also blow air into its coat.
Having a constant need to stay warm in water temperatures that can range between 1.7o and 15.6o C (35o and 60o F), sea otters do not shed their hairs seasonally. They lose a few old hairs at a time and grow replacements throughout the year.
Otters eat at the surface of the water. As food items are found, usually on the ocean bottom, otters maximize their dive time by stashing their catch in loose folds of skin under their forelimbs that form hidden “pouches”. The more food that can be gathered per dive, the less energy is wasted. Sea otters are one of the few animals known to use tools. Rocks, broken shells, and other objects are used for breaking, prying loose and smashing open a food item.
The outer fur hairs cling together when wet, maintaining a thin outer layer that keeps the underfur and the skin dry. The outer fur has an oil coating which also repels water. The fur of the sea otter is believed to be the most fine and dense fur of any animal. There may be up to one million hairs in one square inch of sea otter fur.
The life span of females in the wild is about 12-18 years. Males have a shorter life span, 10-14 years.
Sea otters are protected by international, federal, and state laws and treaties. Sea otters, Enhydra.lutris; are listed on the IUCN Red List as an endangered species. The U.S. Department of Fish and Game lists southern sea otters and the southwestern stock of northern sea otters as threatened.
Humans are the primary source of the rising nonpoint pollution levels in California’s coastal waters. Pollution from agricultural and urban runoff and industrial and municipal discharges are believed to be causative factors in the very slow to stagnant population growth of southern otters. Runoff from the land that enters the marine environment contains chemicals, sediments, excess nutrients, and other contaminants harmful to these marine animals. In addition animal waste from land animals such as raccoons, possums, domestic and feral cats can contain bacteria, parasites, and viruses that cause disease.
Major non-human predators of sea otters include sharks, killer whales, coyotes, brown bears and even eagles. Southern sea otters have been killed illegally because of the belief they compete with commercial fishers and divers collecting sea urchins commercially.
Predators of sea otters include sharks and killer whales. Sea otters dive or play dead when they sense danger, or may signal alarm by raising a forepaw. The Alaskan subspecies have predators on land such as coyotes or brown bears. Bald eagles have been observed swooping down and grabbing sea otter pups.
The southern sea otter has had a high political profile. Its voracious appetite has made it a target of divers competing for abalone, Pismo clams, and sea urchins. Pollution still threatens these marine mammals. Oil spills cause their coats to become matted, allowing the cold water to reach their skin, which can result in death from the cold.
The southern sea otter population is still threatened and its growth is almost stagnant. The U.S. Fish and Wildlife Service conducts southern sea otter counts twice a year. Researchers reported that “the count is ever so slightly up – a good sign. The pup count is sharply down – a bad sign. And year-to-date strandings are sharply up – another bad sign.” The 2010 count found 2,719 otters, slightly up from last year’s count of 2.654 but the three year running average still indicates that recovery of sea otters is not being achieved and the otters are a long way from being delisted. To qualify for such action there must be a count of 3,090 for three continuous years and many scientists believe that this number is too low to sustain the population.
A record 335 otter deaths were counted in 2011. The biggest emerging threat to sea otters— - now causing more other deaths among one segment of the population than all other causes combined— is sharks. This is a startling development that researchers are trying to learn more about. Sharks do not eat sea otters, but more otters are turning up dead as a result of from shark bites.
Sea otters are unique among other animals in the weasel family Mustelidae in that they are able to live their entire life in water; have no functional scent glands; and do not make dens or burrows. At one time researchers suggested that they belonged in the family of earless seals such as the harbor seal.