Enhydra lutris

Geographic Range

Sea otters, Enhydra lutris , are found in two geographic regions on the Pacific Coast: along the Kuril and Commander Islands off the coast of Russia, the Aleutian Islands below the Bering Sea, and the coastal waters off the Alaskan Peninsula to Vancouver Island, Canada; and along the central California coast from Ano Nuevo to Point Sur.

Sea ice limits their northern range to below 57 degrees N lattitude, and the distribution of kelp forests limits the southern range to about 22 degrees N lattitude. Hunting during the 18th and 19th centuries greatly reduced the distribution of sea otters.

Three subspecies of E. lutris are recognized today. Enhydra lutris lutris ranges from the Kuril Islands north to the commander islands in the western pacific. Enhydra lutris nereis is found off the coast of central California. Enhydra lutris kenyoni is distributed throughout the Aleutian Islands and southern Alaska, and has been reintroduced to various locations from south of Prince William Sound, Alaska to Oregon.

• Biogeographic Regions
• nearctic nearctic
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Sea otters inhabit temperate coastal waters with rocky or soft sediment ocean bottom. They live in offshore forests of giant kelp ( Macrocystis pyrifera ), and spend most of their active time foraging below the canopy. They eat, rest, and groom themselves at the water surface. While sea otters are capable of diving to depths of at least 45 meters, they prefer coastal waters up to 30 meters deep. The shallower the water, the less time is spent diving to reach food.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

Alaskan sea otters are slightly larger than Californian otters. Adult male Alaskan otters weigh 27 to 39 kg, while females weigh 16 to 27 kg. Adult male California sea otters average 29 kg in mass, while females average 20 kg. Individuals can weigh as much as 45 kg. Males measure 1.2 to 1.5 m in length, while females measure 1 to 1.4 m. The tail comprises less than a third of the body length, measuring 25 to 35 cm.

The pelage is brown or reddish brown. The fur consists of two layers: a dark undercoat and longer, lighter-colored guard hairs, which trap a layer of air next to the skin to keep it dry. Sea otter fur is the densest of all mammals, with about 100,000 hairs per square centimeter. Because sea otters do not have any insulating fat, the fur is responsible for heat maintenance.

Sea otters have circular, furry faces with short noses, rounded eyes and ears, and long whiskers that assist in foraging for food. The hind legs are long and the paws are broad, flat and webbed. The forelimbs are short and have retractable claws, which help with grooming and eating. Sea otters have patches of loose skin under the forearms that they use to help store tools (usually a rock) so they can have free “hands” while eating, and to transport food during diving. Sea otters are the only carnivores with just 4 lower incisors. Females have two mammae.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

Sea otters are polygynous, with males having multiple female partners throughout the year. Many males actively defend territories. Disputes are usually settled with splashing and vocal displays, and fighting is rare. Males mate with females that inhabit their territory. If no territory is established, they seek out females in estrus. When a male sea otter finds a receptive female, the two engage in playful and sometimes aggressive behavior. They bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior.

• Mating System
• polygynous polygynous

Sea otters can reproduce year round. There are peaks of birth in May to June in the Aleutian Islands and in January to March in California. Sea otters are one of several species of mammals that undergo delayed implantation in which the embryo does not implant during the immediate period following fertilization, but remains in a state of suspended growth allowing for birth to occur under favorable conditions. Delayed implantation produces varied gestation times, which has been reported as 4 to 12 months. Females usually give birth about once a year, though many females experience longer breeding intervals, giving birth every 2 years. If a pup does not survive, the mother may experience postpartum estrus.

Orientation of the fetus may be either caudal or cephalic, although cephalic orientation is more common near birth. A single pup is born weighing 1.4 to 2.3 kg. Twins occur in 2% of births, but only one pup can be raised successfully. Pups typically remain with their mother for 5 to 6 months after birth. Females reach sexual maturity at 4 years of age. Males reach sexual maturity at 5 to 6 years, but may not mate until much later.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous
• delayed implantation delayed implantation
• post-partum estrous

Male sea otters do not provide any care to their offspring. Pups are weaned at around 6 months of age but start to eat solid foods shortly after birth. Females carry their pups on their bellies while they nurse. Their milk is 20 to 25% fat. While a mother is foraging, she wraps her pup in kelp at the water surface to keep it from drifting away. At any sign of a predator, the female clamps onto her pup’s neck with her mouth and dives. Females groom their pups extensively for 3 months as their coat develops. A pup’s coat traps air, which keeps the animal afloat. Pups start diving at 2 months of age. The pup remains dependent on the mother for about 6 to 8 months.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• post-independence association with parents

Lifespan/Longevity

The maximum estimated lifespan of sea otters is 23 years in the wild.

Behavior

Sea otters congregate in groups known as rafts or pods when resting. Females tend to avoid males except when mating. Sea otters are long-lived and typically remain in the same area for years. They spend the majority of their time in the ocean, but rest on land when the population density is high or during stormy weather.

Sea otters utilize vertical undulations of the body to swim, tucking in the forelimbs and using the hind limbs and tail to control their motion. Otters can swim as fast as 9 km per hour under water. Sea otters are diurnal with crepuscular peaks in foraging activity. Foraging dives usually last 50 to 90 seconds, but otters can remain submerged for nearly 6 minutes. Sea otters spend 15 to 55% of their time foraging, depending on food availability.

When resting or sleeping, sea otters float on their back and wrap themselves in kelp to keep from drifting. Their hind limbs stick out of the water and their forelimbs are either folded on their chest or used to cover their eyes. They diligently groom and clean their fur to maintain its insulating ability. Sea otters are one of few mammals that exhibit tool use.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial
• social social

Home Range

Male sea otters have larger home ranges than females. The home range of a male may overlap with that of several females. Same-sex territories do not overlap and are defended by their owners.

Communication and Perception

Sea otters communicate through body contact and vocalizations, although they are not overly vocal. Researchers have recognized nine vocalizations. Pups use squeals to communicate with their mothers. Other calls include coos, whines, distress screams, growls, snarls, and whistles. Scent is important in recognition and surveying physiological states. Each sea otter has its own distinct scent that conveys identity, age, and sex.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Sea otters are carnivorous. They will eat nearly any fish or marine invertebrate they can find in their kelp forest foraging grounds. Their diet consists of marine invertebrate herbivores and filter feeders such as sea urchins ( Strongylocentrotus purpuratus and Strongylocentrotus franciscanus ), sea stars ( Pisaster ochraceus ), limpets ( Diodora aspera ), coast mussels ( Mytilus edulis ), chitons ( Katharina tunicata ), and purple-hinged rock scallops ( Hinnites giganteus ). Otters also eat crabs, octopus, squid, and fish. Individuals tend to be specialized in their choice of prey; one otter may consume only urchins and crabs while another may eat mostly fish, depending on the abilities of the individual and local food availability. Otters consume 20 to 25% of their body weight each day. They obtain most of their water from prey but also drink seawater to satisfy thirst.

Sea otters commonly feed in small groups. Hunting occurs on the sea floor. They use their sensitive whiskers to locate small creatures in the dense kelp beds and crevices. They use their small, agile forepaws to capture prey and to rub, roll, twist, and pull apart prey. Sea otters collect invertebrates in loose folds of skin under their armpits and eat at the surface. The feeding process, including foraging, eating, and cleaning their fur after a meal, lasts 2 to 3 hours. Sea otters usually eat 3 to 4 times a day.

Sea otters break open prey items with hard shells or exoskeletons with a rock. Some otters hold the rock on their chest and drive the prey into the rocks. Others leave the prey on their chests and hit the prey with the rocks. The same rock is kept for many dives. Otters often wash their prey by holding it against their body and turning in the water. Males steal from females if they get a chance. For this reason, females tend to forage in separate areas.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods
  • molluscivore molluscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• echinoderms
• other marine invertebrates

Predation

Great white sharks ( Carcharodon carcharias ) are one of the primary predators of sea otters. Otters are occasionally eaten by coyotes ( Canis lantrans ) after taking refuge on the sand during stormy weather. Young pups left alone on the surface while their mothers feed beneath the surface are preyed upon by bald eagles ( Haliaeetus leucocephalus ). It was once thought that killer whales Orcinus orca were responsible for declines in the sea otter population in Alaska, but evidence is inconclusive.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Sea otters are vital to the overall health and diversity of the kelp forest ecosystem. They are considered a keystone species and play a major role in the community by controlling herbivorous invertebrates. Sea otters prey on sea urchins, thereby preventing sea urchins from overgrazing the kelp forest. This allows the kelp forest to thrive and contributes to an increase in marine diversity. The variety in the sea otter diet reduces competition between benthic grazers and supports greater diversity in those species. The presence of sea otters is believed to be important in the evolution of kelp forest ecosystems.

Two apicomplexan protozoan parasites, Sarcosystis neurona and Toxoplasma gondii infect the sea otter causing encephalitis. An acanthocephalen worm ( Profilicollis ) has also been linked to mortality and decline in the population.

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

The fur of sea otters was of great importance in the fur trade from the mid 1700s to 1911. Their fur was coveted due to its extreme density and insulating quality. Pelts sold for as much as $1,125 each and were fashioned into hats, coats, and other garments sold in Russia, Canada, and the United States.

• Positive Impacts
• body parts are source of valuable material

Economic Importance for Humans: Negative

Sea otters feed on shellfish, sea urchins, and crabs, competing with commercial fisheries.

Conservation Status

Sea otters were hunted to near extinction (1000 to 2000 individuals worldwide) at until the turn of the 20th century when the United States, Russia, Japan, and Great Britain reached an agreement in 1911 called the International Fur Seal Treaty, banning the hunting of fur-bearing sea mammals. In 1972, the U.S. Marine Mammal Protection Act offered further protection by banning capture and harassment of sea mammals. The Exxon Valdez oil spill of 1989 had a dramatic effect on the Alaskan sea otter population, killing approximately 5,000 individuals.

Parasites and infectious disease contribute to sea otter mortality, specifically Toxoplasma gondii , which infects domestic cats, and Sarcosystis neurona , which infects opossums. It is postulated that cat and opossum feces travel to storm drains via runoff and disposal in toilets, eventually coming into contact with sea otters. In September 2006, Governor Arnold Schwarzenegger passed a law raising the maximum fine for harming a sea otter to $25,000, and required that all cat litter sold in California display a warning label that advises not to dump cat feces down storm drains or in toilets.

According to the Otter Foundation, the California sea otter population declined from July 2008 to July 2011. Estimates suggest a California population of approximately 2700 individuals. Enhydra lutris was placed under the Endangered Species Act (ESA) in 1973 and is now listed on CITES Appendix I and II. In Canada, sea otters are protected under the Species at Risk Act. As of 2008, E. lutris is considered endangered by the IUCN. Sea otters are vulnerable to large-scale population declines, with oil spills being the greatest anthropogenic threat.

Additional Links

Encyclopedia of Life

Contributors

Joe Allegra (author), San Diego Mesa College, Rhiannon Rath (author), San Diego Mesa College, Aren Gunderson (author), University of Northern Iowa, Paul Detwiler (editor), San Diego Mesa College, Gail McCormick (editor), Animal Diversity Web Staff.

References

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