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Lifespan, longevity, and ageing

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Maximum longevity: 27 years (captivity) Observations: There is a delayed implantation and the total gestation time varies from 4 to 12 months. The actual embryonic development takes about 4-5.5 months (Ronald Nowak 2003). It has been suggested that longevity in the wild may be as high as 30 years (Bernhard Grzimek 1990), which is dubious. One wild born female was about 27 years old when she died in captivity (Richard Weigl 2005).
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Behavior

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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 ; tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Conservation Status

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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.

US Federal List: threatened

CITES: appendix i; appendix ii

State of Michigan List: no special status

IUCN Red List of Threatened Species: endangered

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Benefits

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

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Benefits

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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

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Associations

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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

Commensal/Parasitic Species:

  • Acanthocephalan worm Profilicollis
  • Apicomplexan protozoan << Sarcocystis neurona>>
  • Apicomplexan protozoan Toxoplasma gondii
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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Trophic Strategy

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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 (Crassadoma gigantea). 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.

Animal Foods: fish; mollusks; aquatic crustaceans; echinoderms; other marine invertebrates

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Distribution

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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 (Native ); pacific ocean (Native )

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Habitat

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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.

Range depth: 45 to 0 m.

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: coastal

Other Habitat Features: intertidal or littoral

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Life Expectancy

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

Typical lifespan
Status: wild:
23 (high) years.

Average lifespan
Sex: male
Status: captivity:
19.0 years.

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Morphology

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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.

Range mass: 14 to 45 kg.

Range length: 1 to 1.5 m.

Sexual Dimorphism: male larger

Other Physical Features: endothermic ; bilateral symmetry

Average basal metabolic rate: 98.479 W.

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
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Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Associations

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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.

Known Predators:

  • Coyotes Canis lantrans
  • Great white sharks Carcharadon charcarias
  • Bald eagles Haliaeetus leucocephalus
  • Killer whales Orcinus orca
  • California sea lions Zalophus californianus
  • Humans Homo sapiens

Anti-predator Adaptations: cryptic

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Reproduction

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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

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.

Breeding interval: Sea otters breed once every 1 or 2 years.

Breeding season: Sea otters breed year round.

Range number of offspring: 1 to 2.

Average number of offspring: 1.

Range gestation period: 4 to 12 months.

Average gestation period: 6 months.

Average weaning age: 6 months.

Range age at sexual or reproductive maturity (female): 4 to 5 years.

Range age at sexual or reproductive maturity (male): 5 to 8 years.

Average age at sexual or reproductive maturity (male): 6 years.

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

Average birth mass: 1868 g.

Average number of offspring: 1.

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 ; 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

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Allegra, J.; R. Rath and A. Gunderson 2012. "Enhydra lutris" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html
author
Joe Allegra, San Diego Mesa College
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Rhiannon Rath, San Diego Mesa College
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Aren Gunderson, University of Northern Iowa
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Paul Detwiler, San Diego Mesa College
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Gail McCormick, Special Projects
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Biology

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Highly aquatic, the sea otter rarely comes ashore, both resting and feeding in coastal waters. Alaskan sea otters are more at home out of the water than their Californian relatives, often hauling out on sandbars and ice (8). Otters have a high metabolic rate (9) and these resourceful, opportunistic predators need to consume 25 percent of their body weight a day (6). Diving to depths of up to 75 metres they retrieve invertebrates such as mussels, snails, crabs and urchins from the seabed (6). Pouches of skin at the armpit of each forelimb can be used to store food whilst it is carried to the surface (6). Otters float on their backs, using their chest as a table whilst they attempt to prize open the shells. Sometimes rocks are used to smash open the hard shells and sea otters are one of the only mammals (apart from primates) to have developed tool use (6). Sea otters are considered a 'keystone species' in some parts of their range, as they appear to be vital in the maintenance of kelp forest ecosystems by suppressing the number of sea urchins that would otherwise overgraze the forests (4). These gregarious creatures can be found in large same-sex groups known as 'rafts'. Rafts in California rarely exceed 50 individuals but in Alaska, where the population density is higher, up to 2,000 otters can gather (2). Sea otters probably spend more time and energy grooming their fur that any other mammal; an important activity required to maintain the insulation of their fur, as it cleans and replenishes air to the under fur (4). Grooming involves rubbing, rolling and blowing air into the fur (4). Trapped air in the under fur is heated by the body to provide insulation and gives otters a silvery appearance underwater (5). Sea otters are polygynous, with adult males generally defending territories that encompass the ranges of several females (2) (4). While mating, the male will grip the female's nose with his teeth and she is often left with a bloody souvenir of their encounter (4). Females usually give birth to a single pup and carry them on their chest, nursing them and grooming them meticulously to ensure the fur remains buoyant and insulated (9). Young pups are left on the surface whilst their mother dives for food, but as they mature they follow her, learning to forage by watching her technique (5). Pups will stay with their mother for around three to six moths (6).
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Conservation

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The sea otter is legally protected in the United States under the Marine Mammal Protection Act and in Canada sea otters are protected under the Species at Risk Act (10). Despite protection and various conservation measures, the Californian population has been slow to recover; a new Recovery Plan by the U.S. Fish and Wildlife Service was currently being developed with the aim of managing damaging human activities to enable the population to recover to a point where it can be removed from the List of Endangered and Threatened Wildlife (11). There have been several successful reintroduction attempts along the west coast of North America, restoring this highly appealing animal to much of its former range (2).
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Description

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The sea otter, the smallest marine mammal in the world, is well adapted for its predominately aquatic lifestyle, possessing a strong, rudder-like tail and large hind-feet that act as flippers (2). Unlike other marine mammals, sea otters do not have blubber and instead rely on their fur to keep warm in the water (4); their reddish-brown coat is the densest of any mammal, consisting of around 100,000 hairs per cm² (2). The natural oils produced by the fur provide a waterproof quality (5).
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Habitat

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Sea otters inhabit near-shore rocky or soft-bottom coastal waters, and in California are particularly associated with dense kelp forests (4).
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Range

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Historically, the sea otter was found in coastal areas throughout the North Pacific (6). Sea otters can still be found in much of this former range although numbers are greatly reduced and populations fragmented (6). Three subspecies are currently recognised: the southern, or California sea otter (Enhydra lutris nereis), occurs from California to Mexico; the northern, or Alaskan sea otter (E. l. kenyoni), is found along the northwest coast of North America and into Alaska; and the Russian sea otter (E. l. lutris) occurs in the western north Pacific (7). Alaska plays host to possibly as much as 90 percent of the world population of this species (6).
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Status

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Classified as Endangered (EN) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).
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Threats

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Since the 1700s, prior to the commercial fur trade, native peoples throughout the otter's range harvested sea otters for their pelts (2). An intensive commercial fur trade, from 1740 until about 1900, resulted in the sea otter being harvested almost to extinction, and by 1900, the sea otter was so rare that commercial harvesting was forced to cease (6). Sea otters were protected by an international treaty in 1911. Since then, numbers have recovered to an extent, but human activities, especially coastal development and marine pollution, now pose a threat to the sea otter (6). In 1989, hundreds, and possibly thousands, of sea otters were killed as a direct result of the Exxon Valdez oil spill in Prince William Sound in Alaska (4). The possibility of another major oil spill poses a continual threat to the sea otter, and could have devastating consequences. Additional threats include entanglement in fishing gear, particularly gill nets, and competition with commercial fisheries for food (6). In the central Aleutian Islands, Alaska, sea otters have declined by as much as 90 percent (4). Evidence indicates that this drastic decline is the result of increased predation by killer whales, which have switched to consuming more sea otters following the collapse of Steller's sea lion and harbour seal populations in the region (4).
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Diagnostic Description

provided by FAO species catalogs
The sea otter is the most derived of the otters. The muzzle has a set of thick vibrissae. The large head has a blunt snout, and is connected to the body by a short, stocky neck. The forelimbs are short and similar to those of other otters, with a loose flap of skin under each that is used to store food. The hindlimbs are large and flattened like flippers; they are oriented backwards. Although the short tail is not noticeably tapered, it is flattened top to bottom into a paddle-like structure. Three subspecies are currently recognized (described below).

The pelage of sea otters is the densest of any mammal (more than 100 000 hairs/cm2). A layer of sparse guard hairs overlays the dense underfur. Sea otters are completely covered with fur, except for the nose pad, inside of the ear flaps, and the pads on the bottom of the feet. The colour of the fur is dark brown to reddish brown. Older individuals become grizzled, with the fur around the head, neck, and shoulders becoming almost white.

The dental formula is I 3/2, C 1/1, PM 3/3, M 1/2.

Can be confused with: The sea otter is the only truly marine otter in its range, although North American river otters (Lutra cunadensis) are often found in marine waters along the northwest coast of North America. River otters are smaller and more slender than sea otters, with longer tails. Also, river otters generally swim belly down even at the surface, while sea otters usually move along the surface on their backs.

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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Size

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Male sea otters reach lengths of 148 cm and weights of 45 kg. Females can be up to 140 cm and 32.5 kg. Newborns weigh about 1.0 to 1.9 kg.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Brief Summary

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Sea otters can be seen singly or in groups (most often resting groups called rafts). Rafts in California rarely exceed 50 individuals, but those in Alaska can contain up to 2 000 otters. Sea otters are polygynous: males tend to defend large territories that encompass the ranges of several females. Pupping occurs throughout the year, but peaks in May to June in Alaska, and in December to February in California. During mating, the male bites the nose of the female to position himself; thus, females often have nose scars (these are useful to researchers in identification of individuals).

Sea otters feed on or near the bottom in shallow waters (often in kelp beds). Major prey items are benthic invertebrates such as abalones, sea urchins, and rock crabs. However, sea otters also eat other shellfishes, cephalopods, and sluggish near-bottom fishes.

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bibliographic citation
Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Benefits

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Conservation Status : Sea otters have been commercially hunted since the 1700s, mostly for their pelts. All 3 subspecies were significantly reduced. Protection was finally afforded in some areas near the turn of this century. Oil spills and catches in net are the major remaining threats. IUCN:

Not listed.

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cc-by-nc-sa-3.0
bibliographic citation
Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
author
Food and Agriculture Organization of the UN
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FAO species catalogs

Sea otter

provided by wikipedia EN

The sea otter (Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg (31 and 99 lb), making them the heaviest members of the weasel family, but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.

The sea otter inhabits nearshore environments, where it dives to the sea floor to forage. It preys mostly on marine invertebrates such as sea urchins, various mollusks and crustaceans, and some species of fish. Its foraging and eating habits are noteworthy in several respects. Its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. In most of its range, it is a keystone species, controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems.[3] Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries.

Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 1741 and 1911, and the world population fell to 1,000–2,000 individuals living in a fraction of their historic range.[4] A subsequent international ban on hunting, sea otter conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species occupies about two-thirds of its former range. The recovery of the sea otter is considered an important success in marine conservation, although populations in the Aleutian Islands and California have recently declined or have plateaued at depressed levels. For these reasons, the sea otter remains classified as an endangered species.

Evolution

The sea otter is the heaviest (the giant otter is longer, but significantly slimmer) member of the family Mustelidae,[5] a diverse group that includes the 13 otter species and terrestrial animals such as weasels, badgers, and minks. It is unique among the mustelids in not making dens or burrows, in having no functional anal scent glands,[6] and in being able to live its entire life without leaving the water.[7] The only living member of the genus Enhydra, the sea otter is so different from other mustelid species that, as recently as 1982, some scientists believed it was more closely related to the earless seals.[8] Genetic analysis indicates the sea otter and its closest extant relatives, which include the African speckle-throated otter, European otter, African clawless otter and oriental small-clawed otter, shared an ancestor approximately 5 million years ago.[9]

Fossil evidence indicates the Enhydra lineage became isolated in the North Pacific approximately 2 million years ago, giving rise to the now-extinct Enhydra macrodonta and the modern sea otter, Enhydra lutris.[10] One related species has been described, Enhydra reevei, from the Pleistocene of East Anglia.[11] The modern sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands, mainland Alaska, and down the North American coast.[12] In comparison to cetaceans, sirenians, and pinnipeds, which entered the water approximately 50, 40, and 20 million years ago, respectively, the sea otter is a relative newcomer to a marine existence.[13] In some respects, though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth.[14] The full genome of the northern sea otter (Enhydra lutris kenyoni) was sequenced in 2017 and may allow for examination of the sea otter's evolutionary divergence from terrestrial mustelids.[15]

Taxonomy

Lutrinae

Pteronura (giant otter)

       

Lontra (4 species)

       

Enhydra (sea otter)

   

Hydrictis
(spotted-necked otter)

       

Lutra (2 species)

         

Aonyx
(African clawless)

       

Amblonyx
(Asian small-clawed)

   

Lutrogale
(smooth-coated)

              Cladogram showing relationships between sea otters and other otters[16][17]

The first scientific description of the sea otter is contained in the field notes of Georg Steller from 1751, and the species was described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae.[18] Originally named Lutra marina, it underwent numerous name changes before being accepted as Enhydra lutris in 1922.[10] The generic name Enhydra, derives from the Ancient Greek en/εν "in" and hydra/ύδρα "water",[19] meaning "in the water", and the Latin word lutris, meaning "otter".[20]

The sea otter was formerly sometimes referred to as the "sea beaver",[21] as the marine fur-bearer was similar in commercial value to the terrestrial beaver. Rodents (of which the beaver is one) are not closely related to otters, which are carnivorans. It is not to be confused with the marine otter, a rare otter species native to the southern west coast of South America. A number of other otter species, while predominantly living in fresh water, are commonly found in marine coastal habitats. The extinct sea mink of northeastern North America is another mustelid that had adapted to a marine environment.

Subspecies

Three subspecies of the sea otter are recognized with distinct geographical distributions. Enhydra lutris lutris (nominate), the Asian sea otter, ranges from the Kuril Islands north of Japan to Russia's Commander Islands in the western Pacific Ocean. In the eastern Pacific Ocean, E. l. kenyoni, the northern sea otter, is found from Alaska's Aleutian Islands to Oregon and E. l. nereis, the southern sea otter, is native to central and southern California.[22] The Asian sea otter is the largest subspecies and has a slightly wider skull and shorter nasal bones than both other subspecies. Northern sea otters possess longer mandibles (lower jaws) while southern sea otters have longer rostrums and smaller teeth.[23][24]

Description

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A sea otter's thick fur makes its body appear plumper on land than in the water.
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Skull of a sea otter

The sea otter is one of the smallest marine mammal species, but it is the heaviest mustelid.[7] Male sea otters usually weigh 22 to 45 kg (49 to 99 lb) and are 1.2 to 1.5 m (3 ft 11 in to 4 ft 11 in) in length, though specimens up to 54 kg (119 lb) have been recorded.[25] Females are smaller, weighing 14 to 33 kg (31 to 73 lb) and measuring 1.0 to 1.4 m (3 ft 3 in to 4 ft 7 in) in length.[26] For its size, the male otter's baculum is very large, massive and bent upwards, measuring 150 mm (5.9 in) in length and 15 mm (0.59 in) at the base.[27]

Unlike most other marine mammals, the sea otter has no blubber and relies on its exceptionally thick fur to keep warm.[28] With up to 150,000 strands of hair per square centimetre (nearly one million per sq in), its fur is the densest of any animal.[29] The fur consists of long, waterproof guard hairs and short underfur; the guard hairs keep the dense underfur layer dry.[26] There is an air compartment between the thick fur and the skin where air is trapped and heated by the body.[30] Cold water is kept completely away from the skin and heat loss is limited.[26] However, this air compartment can be disadvantageous because as the sea otter dives deeper into the water column, the air compartment compresses and heat needed to warm the body is lost.[30] The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct molting season.[31] As the ability of the guard hairs to repel water depends on utmost cleanliness, the sea otter has the ability to reach and groom the fur on any part of its body, taking advantage of its loose skin and an unusually supple skeleton.[32] The coloration of the pelage is usually deep brown with silver-gray speckles, but it can range from yellowish or grayish brown to almost black.[33] In adults, the head, throat, and chest are lighter in color than the rest of the body.[33]

The sea otter displays numerous adaptations to its marine environment. The nostrils and small ears can close.[34] The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully webbed.[35] The fifth digit on each hind foot is longest, facilitating swimming while on its back, but making walking difficult.[36] The tail is fairly short, thick, slightly flattened, and muscular. The front paws are short with retractable claws, with tough pads on the palms that enable gripping slippery prey.[37] The bones show osteosclerosis, increasing their density to reduce buoyancy.[38]

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Skull, illustration

The sea otter propels itself underwater by moving the rear end of its body, including its tail and hind feet, up and down,[35] and is capable of speeds of up to 9 km/h (5.6 mph).[5] When underwater, its body is long and streamlined, with the short forelimbs pressed closely against the chest.[39] When at the surface, it usually floats on its back and moves by sculling its feet and tail from side to side.[40] At rest, all four limbs can be folded onto the torso to conserve heat, whereas on particularly hot days, the hind feet may be held underwater for cooling.[41] The sea otter's body is highly buoyant because of its large lung capacity – about 2.5 times greater than that of similar-sized land mammals[42] – and the air trapped in its fur. The sea otter walks with a clumsy, rolling gait on land, and can run in a bounding motion.[36]

Long, highly sensitive whiskers and front paws help the sea otter find prey by touch when waters are dark or murky.[43] Researchers have noted when they approach in plain view, sea otters react more rapidly when the wind is blowing towards the animals, indicating the sense of smell is more important than sight as a warning sense.[44] Other observations indicate the sea otter's sense of sight is useful above and below the water, although not as good as that of seals.[45] Its hearing is neither particularly acute nor poor.[46]

An adult's 32 teeth, particularly the molars, are flattened and rounded for crushing rather than cutting food.[47] Seals and sea otters are the only carnivores with two pairs of lower incisor teeth rather than three;[48] the adult dental formula is 3.1.3.12.1.3.2.[49] The teeth and bones are sometimes stained purple as a result of ingesting sea urchins.[50] The sea otter has a metabolic rate two or three times that of comparatively sized terrestrial mammals. It must eat an estimated 25 to 38% of its own body weight in food each day to burn the calories necessary to counteract the loss of heat due to the cold water environment.[51][52] Its digestive efficiency is estimated at 80 to 85%,[53] and food is digested and passed in as little as three hours.[28] Most of its need for water is met through food, although, in contrast to most other marine mammals, it also drinks seawater. Its relatively large kidneys enable it to derive fresh water from sea water and excrete concentrated urine.[54]

Behavior

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Sensitive vibrissae and forepaws enable sea otters to find prey (like this purple sea urchin) using their sense of touch.

The sea otter is diurnal. It has a period of foraging and eating in the morning, starting about an hour before sunrise, then rests or sleeps in mid-day.[55] Foraging resumes for a few hours in the afternoon and subsides before sunset, and a third foraging period may occur around midnight.[55] Females with pups appear to be more inclined to feed at night.[55] Observations of the amount of time a sea otter must spend each day foraging range from 24 to 60%, apparently depending on the availability of food in the area.[56]

Sea otters spend much of their time grooming, which consists of cleaning the fur, untangling knots, removing loose fur, rubbing the fur to squeeze out water and introduce air, and blowing air into the fur. To casual observers, it appears as if the animals are scratching, but they are not known to have lice or other parasites in the fur.[57] When eating, sea otters roll in the water frequently, apparently to wash food scraps from their fur.[58]

Foraging

The sea otter hunts in short dives, often to the sea floor. Although it can hold its breath for up to five minutes,[34] its dives typically last about one minute and not more than four.[26] It is the only marine animal capable of lifting and turning over rocks, which it often does with its front paws when searching for prey.[58] The sea otter may also pluck snails and other organisms from kelp and dig deep into underwater mud for clams.[58] It is the only marine mammal that catches fish with its forepaws rather than with its teeth.[28]

Under each foreleg, the sea otter has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left one), the animal stores collected food to bring to the surface. This pouch also holds a rock, unique to the otter, that is used to break open shellfish and clams.[59] At the surface, the sea otter eats while floating on its back, using its forepaws to tear food apart and bring it to its mouth. It can chew and swallow small mussels with their shells, whereas large mussel shells may be twisted apart.[60] It uses its lower incisor teeth to access the meat in shellfish.[61] To eat large sea urchins, which are mostly covered with spines, the sea otter bites through the underside where the spines are shortest, and licks the soft contents out of the urchin's shell.[60]

The sea otter's use of rocks when hunting and feeding makes it one of the few mammal species to use tools.[62] To open hard shells, it may pound its prey with both paws against a rock on its chest. To pry an abalone off its rock, it hammers the abalone shell using a large stone, with observed rates of 45 blows in 15 seconds.[26] Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, requires multiple dives.[26]

Social structure

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Sleeping sea otters holding paws at the Vancouver Aquarium[63] are kept afloat by their naturally high buoyancy.

Although each adult and independent juvenile forages alone, sea otters tend to rest together in single-sex groups called rafts. A raft typically contains 10 to 100 animals, with male rafts being larger than female ones.[64] The largest raft ever seen contained over 2000 sea otters. To keep from drifting out to sea when resting and eating, sea otters may wrap themselves in kelp.[65]

A male sea otter is most likely to mate if he maintains a breeding territory in an area that is also favored by females.[66] As autumn is the peak breeding season in most areas, males typically defend their territory only from spring to autumn.[66] During this time, males patrol the boundaries of their territories to exclude other males,[66] although actual fighting is rare.[64] Adult females move freely between male territories, where they outnumber adult males by an average of five to one.[66] Males that do not have territories tend to congregate in large, male-only groups,[66] and swim through female areas when searching for a mate.[67]

The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a gull.[68] Females coo when they are apparently content; males may grunt instead.[69] Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream.[68] Although sea otters can be playful and sociable, they are not considered to be truly social animals.[70] They spend much time alone, and each adult can meet its own hunting, grooming, and defense needs.[70]

Reproduction and life cycle

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While mating the male bites the nose of the female, often bloodying and scarring it.

Sea otters are polygynous: males have multiple female partners. However, temporary pair-bonding occurs for a few days between a female in estrus and her mate.[58] Mating takes place in the water and can be violent and non-consensual. The male commonly bites the female on the muzzle – which often leaves scars on the nose – and sometimes holds her head under water.[5][71]

Births occur year-round, with peaks between May and June in northern populations and between January and March in southern populations.[72] Gestation appears to vary from four to twelve months, as the species is capable of delayed implantation followed by four months of pregnancy.[72] In California, sea otters usually breed every year, about twice as often as those in Alaska.[73]

Birth usually takes place in the water and typically produces a single pup weighing 1.4 to 2.3 kg (3 to 5 lb).[74] Twins occur in 2% of births; however, usually only one pup survives.[5] At birth, the eyes are open, ten teeth are visible, and the pup has a thick coat of baby fur.[75] Mothers have been observed to lick and fluff a newborn for hours; after grooming, the pup's fur retains so much air, the pup floats like a cork and cannot dive.[76] The fluffy baby fur is replaced by adult fur after about 13 weeks.[18]

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A mother floats with her pup on her chest. Georg Steller wrote, "They embrace their young with an affection that is scarcely credible."[77]

Nursing lasts six to eight months in Californian populations and four to twelve months in Alaska, with the mother beginning to offer bits of prey at one to two months.[78] The milk from a sea otter's two abdominal nipples is rich in fat and more similar to the milk of other marine mammals than to that of other mustelids.[79] A pup, with guidance from its mother, practices swimming and diving for several weeks before it is able to reach the sea floor. Initially, the objects it retrieves are of little food value, such as brightly colored starfish and pebbles.[59] Juveniles are typically independent at six to eight months, but a mother may be forced to abandon a pup if she cannot find enough food for it;[80] at the other extreme, a pup may nurse until it is almost adult size.[74] Pup mortality is high, particularly during an individual's first winter – by one estimate, only 25% of pups survive their first year.[80] Pups born to experienced mothers have the highest survival rates.[81]

Females perform all tasks of feeding and raising offspring, and have occasionally been observed caring for orphaned pups.[82] Much has been written about the level of devotion of sea otter mothers for their pups – a mother gives her infant almost constant attention, cradling it on her chest away from the cold water and attentively grooming its fur.[83] When foraging, she leaves her pup floating on the water, sometimes wrapped in kelp to keep it from floating away;[84] if the pup is not sleeping, it cries loudly until she returns.[85] Mothers have been known to carry their pups for days after the pups' deaths.[77]

Females become sexually mature at around three or four years of age and males at around five; however, males often do not successfully breed until a few years later.[86] A captive male sired offspring at age 19.[74] In the wild, sea otters live to a maximum age of 23 years,[26] with lifespans ranging from 10 to 15 years for males and 15–20 years for females.[87] Several captive individuals have lived past 20 years, and a female at the Seattle Aquarium died at the age of 28 years.[88] Sea otters in the wild often develop worn teeth, which may account for their apparently shorter lifespans.[89]

Population and distribution

Sea otters live in coastal waters 15 to 23 metres (50 to 75 ft) deep,[90] and usually stay within a kilometre (⅔ mi) of the shore.[91] They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick kelp forests, and barrier reefs.[92] Although they are most strongly associated with rocky substrates, sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt.[93] Their northern range is limited by ice, as sea otters can survive amidst drift ice but not land-fast ice.[94] Individuals generally occupy a home range a few kilometres long, and remain there year-round.[95]

The sea otter population is thought to have once been 150,000 to 300,000,[21] stretching in an arc across the North Pacific from northern Japan to the central Baja California Peninsula in Mexico. The fur trade that began in the 1740s reduced the sea otter's numbers to an estimated 1,000 to 2,000 members in 13 colonies. Hunting records researched by historian Adele Ogden place the westernmost limit of the hunting grounds off the northern Japanese island of Hokkaido and the easternmost limit off Punta Morro Hermosa about 21.5 miles (34.6 km) south of Punta Eugenia, Baja California's westernmost headland in Mexico.[96]

In about two-thirds of its former range, the species is at varying levels of recovery, with high population densities in some areas and threatened populations in others. Sea otters currently have stable populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, with reports of recolonizations in Mexico and Japan.[97] Population estimates made between 2004 and 2007 give a worldwide total of approximately 107,000 sea otters.[18][98][99][100][101]

Japan

Adele Ogden wrote in The California Sea Otter Trade that sea otter were hunted "from Yezo northeastward past the Kuril Group and Kamchatka to the Aleutian Chain".[96] "Yezo" refers to the island of Hokkaido in northern Japan; the only confirmed sea otter population in Japanese territory is on the coast surrounding the town of Erimo, Hokkaido.[1]

Russia

Currently, the most stable and secure part of the sea otter's range is Russia.[102] Before the 19th century, around 20,000 to 25,000 sea otters lived near the Kuril Islands, with more near Kamchatka and the Commander Islands. After the years of the Great Hunt, the population in these areas, currently part of Russia, was only 750.[98] By 2004, sea otters had repopulated all of their former habitat in these areas, with an estimated total population of about 27,000. Of these, about 19,000 are at the Kurils, 2,000 to 3,500 at Kamchatka and another 5,000 to 5,500 at the Commander Islands.[98] Growth has slowed slightly, suggesting the numbers are reaching carrying capacity.[98]

British Columbia

Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with the last sea otter taken near Kyuquot in 1929. From 1969 to 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island. This population increased to over 5,600 in 2013 with an estimated annual growth rate of 7.2%, and their range on the island's west coast extended north to Cape Scott and across the Queen Charlotte Strait to the Broughton Archipelago and south to Clayoquot Sound and Tofino.[103][104] In 1989, a separate colony was discovered in the central British Columbia coast. It is not known if this colony, which numbered about 300 animals in 2004, was founded by transplanted otters or was a remnant population that had gone undetected.[100] By 2013, this population exceeded 1,100 individuals, was increasing at an estimated 12.6% annual rate, and its range included Aristazabal Island, and Milbanke Sound south to Calvert Island.[103] In 2008, Canada determined the status of sea otters to be "special concern".[105][106]

United States

Alaska

Alaska is the central area of the sea otter's range. In 1973, the population in Alaska was estimated at between 100,000 and 125,000 animals.[107] By 2006, though, the Alaska population had fallen to an estimated 73,000 animals.[99] A massive decline in sea otter populations in the Aleutian Islands accounts for most of the change; the cause of this decline is not known, although orca predation is suspected.[108] The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill, which killed thousands of sea otters in 1989.[58]

Washington

In 1969 and 1970, 59 sea otters were translocated from Amchitka Island to Washington, and released near La Push and Point Grenville. The translocated population is estimated to have declined to between 10 and 43 individuals before increasing, reaching 208 individuals in 1989. As of 2017, the population was estimated at over 2,000 individuals, and their range extends from Point Grenville in the south to Cape Flattery in the north and east to Pillar Point along the Strait of Juan de Fuca.[18]

In Washington, sea otters are found almost exclusively on the outer coasts. They can swim as close as six feet off shore along the Olympic coast. Reported sightings of sea otters in the San Juan Islands and Puget Sound almost always turn out to be North American river otters, which are commonly seen along the seashore. However, biologists have confirmed isolated sightings of sea otters in these areas since the mid-1990s.[18]

Oregon

The last native sea otter in Oregon was probably shot and killed in 1906. In 1970 and 1971, a total of 95 sea otters were transplanted from Amchitka Island, Alaska to the Southern Oregon coast. However, this translocation effort failed and otters soon again disappeared from the state.[109] In 2004, a male sea otter took up residence at Simpson Reef off of Cape Arago for six months. This male is thought to have originated from a colony in Washington, but disappeared after a coastal storm.[110] On 18 February 2009, a male sea otter was spotted in Depoe Bay off the Oregon Coast. It could have traveled to the state from either California or Washington.[111] Two sea otters were observed about one mile north of the Winchuck River off the Southern Oregon coast on July 13, 2020.

California

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California's remote areas of coastline sheltered small colonies of sea otters through the fur trade. The 50 that survived in California, which were rediscovered in 1938, have since reproduced to almost 3,000.

The historic population of California sea otters was estimated at 16,000 before the fur trade decimated the population, leading to their assumed extinction. Today's population of California sea otters are the descendants of a single colony of about 50 sea otters located near Bixby Creek Bridge in March 1938 by Howard G. Sharpe, owner of the nearby Rainbow Lodge on Bixby Bridge in Big Sur.[112][113][114] Their principal range has gradually expanded and extends from Pigeon Point in San Mateo County to Santa Barbara County.[115]

Sea otters were once numerous in San Francisco Bay.[116][117] Historical records revealed the Russian-American Company sneaked Aleuts into San Francisco Bay multiple times, despite the Spanish capturing or shooting them while hunting sea otters in the estuaries of San Jose, San Mateo, San Bruno and around Angel Island.[96] The founder of Fort Ross, Ivan Kuskov, finding otters scarce on his second voyage to Bodega Bay in 1812, sent a party of Aleuts to San Francisco Bay, where they met another Russian party and an American party, and caught 1,160 sea otters in three months.[118] By 1817, sea otters in the area were practically eliminated and the Russians sought permission from the Spanish and the Mexican governments to hunt further and further south of San Francisco.[119] Remnant sea otter populations may have survived in the bay until 1840, when the Rancho Punta de Quentin was granted to Captain John B. R. Cooper, a sea captain from Boston, by Mexican Governor Juan Bautista Alvarado along with a license to hunt sea otters, reportedly then prevalent at the mouth of Corte Madera Creek.[120]

In the late 1980s, the USFWS relocated about 140 southern sea otters to San Nicolas Island in southern California, in the hope of establishing a reserve population should the mainland be struck by an oil spill. To the surprise of biologists, the majority of the San Nicolas sea otters swam back to the mainland.[121] Another group of twenty swam 74 miles (119 km) north to San Miguel Island, where they were captured and removed.[122] By 2005, only 30 sea otters remained at San Nicolas,[123] although they were slowly increasing as they thrived on the abundant prey around the island.[121] The plan that authorized the translocation program had predicted the carrying capacity would be reached within five to 10 years.[124] The spring 2016 count at San Nicolas Island was 104 sea otters, continuing a 5-year positive trend of over 12% per year.[125] Sea otters were observed twice in Southern California in 2011, once near Laguna Beach and once at Zuniga Point Jetty, near San Diego. These are the first documented sightings of otters this far south in 30 years.[126]

When the USFWS implemented the translocation program, it also attempted, in 1986, to implement "zonal management" of the Californian population. To manage the competition between sea otters and fisheries, it declared an "otter-free zone" stretching from Point Conception to the Mexican border. In this zone, only San Nicolas Island was designated as sea otter habitat, and sea otters found elsewhere in the area were supposed to be captured and relocated. These plans were abandoned after many translocated otters died and also as it proved impractical to capture the hundreds of otters which ignored regulations and swam into the zone.[127] However, after engaging in a period of public commentary in 2005, the Fish and Wildlife Service failed to release a formal decision on the issue.[123] Then, in response to lawsuits filed by the Santa Barbara-based Environmental Defense Center and the Otter Project, on 19 December 2012 the USFWS declared that the "no otter zone" experiment was a failure, and will protect the otters re-colonizing the coast south of Point Conception as threatened species.[128] Although abalone fisherman blamed the incursions of sea otters for the decline of abalone, commercial abalone fishing in southern California came to an end from overfishing in 1997, years before significant otter moved south of Point Conception. In addition, white abalone (Haliotis sorenseni), a species never overlapping with sea otter, had declined in numbers 99% by 1996, and became the first marine invertebrate to be federally listed as endangered.[129]

Although the southern sea otter's range has continuously expanded from the remnant population of about 50 individuals in Big Sur since protection in 1911, from 2007 to 2010, the otter population and its range contracted and since 2010 has made little progress.[130][131] As of spring 2010, the northern boundary had moved from about Tunitas Creek to a point 2 km southeast of Pigeon Point, and the southern boundary has moved along the Gaviota Coast from approximately Coal Oil Point to Gaviota State Park.[132] A toxin called microcystin, produced by a type of cyanobacteria (Microcystis), seems to be concentrated in the shellfish the otters eat, poisoning them. Cyanobacteria are found in stagnant water enriched with nitrogen and phosphorus from septic tank and agricultural fertilizer runoff, and may be flushed into the ocean when streamflows are high in the rainy season.[133][134] A record number of sea otter carcasses were found on California's coastline in 2010, with increased shark attacks an increasing component of the mortality.[135] Great white sharks do not consume relatively fat-poor sea otters but shark-bitten carcasses have increased from 8% in the 1980s to 15% in the 1990s and to 30% in 2010 and 2011.[136]

For southern sea otters to be considered for removal from threatened species listing, the U.S. Fish and Wildlife Service (USFWS) determined that the population should exceed 3,090 for three consecutive years.[130] In response to recovery efforts, the population climbed steadily from the mid-20th century through the early 2000s, then remained relatively flat from 2005 to 2014 at just under 3,000. There was some contraction from the northern (now Pigeon Point) and southern limits of the sea otter's range during the end of this period, circumstantially related to an increase in lethal shark bites, raising concerns that the population had reached a plateau.[137] However, the population increased markedly from 2015 to 2016, with the United States Geological Survey (USGS) California sea otter survey 3-year average reaching 3,272 in 2016, the first time it exceeded the threshold for delisting from the Endangered Species Act (ESA).[125] If populations continued to grow and ESA delisting occurred, southern sea otters would still be fully protected by state regulations and the Marine Mammal Protection Act, which set higher thresholds for protection, at approximately 8,400 individuals.[138] However, ESA delisting seems unlikely due to a precipitous population decline recorded in the spring 2017 USGS sea otter survey count, from the 2016 high of 3,615 individuals to 2,688, a loss of 25% of the California sea otter population.[139]

Mexico

Historian Adele Ogden described sea otters are particularly abundant in "Lower California", now the Baja California Peninsula, where "seven bays...were main centers". The southernmost limit was Punta Morro Hermoso about 21.5 miles (34.6 km) south of Punta Eugenia, in turn a headland at the southwestern end of Sebastián Vizcaíno Bay, on the west coast of the Baja Peninsula. Otter were also taken from San Benito Island, Cedros Island, and Isla Natividad in the Bay.[96] By the early 1900s, Baja's sea otters were extirpated by hunting. In a 1997 survey, small numbers of sea otters, including pups, were reported by local fishermen, but scientists could not confirm these accounts.[140] However, male and female otters have been confirmed by scientists off shores of the Baja Peninsula in a 2014 study, who hypothesize that otter dispersed there beginning in 2005. These sea otter may have dispersed from San Nicolas Island, which is 300 kilometres (190 mi) away, as individuals have been recorded traversing distances of over 800 kilometres (500 mi). Genetic analysis of most of these animals were consistent with California, i.e. United States, otter origins, however one otter had a haplotype not previously reported, and could represent a remnant of the original native Mexican otter population.[141]

Ecology

Diet

High energetic requirements of sea otter metabolism require them to consume at least 20% of their body weight a day.[30] Surface swimming and foraging are major factors in their high energy expenditure due to drag on the surface of the water when swimming and the thermal heat loss from the body during deep dives when foraging.[142][30] Sea otter muscles are specially adapted to generate heat without physical activity.[143]

Sea otters consume over 100 prey species.[144] In most of its range, the sea otter's diet consists almost exclusively of marine benthic invertebrates, including sea urchins, fat innkeeper worms, a variety of bivalves such as clams and mussels, abalone, other mollusks, crustaceans, and snails.[144][145] Its prey ranges in size from tiny limpets and crabs to giant octopuses.[144] Where prey such as sea urchins, clams, and abalone are present in a range of sizes, sea otters tend to select larger items over smaller ones of similar type.[144] In California, they have been noted to ignore Pismo clams smaller than 3 inches (7 cm) across.[146]

In a few northern areas, fish are also eaten. In studies performed at Amchitka Island in the 1960s, where the sea otter population was at carrying capacity, 50% of food found in sea otter stomachs was fish.[147] The fish species were usually bottom-dwelling and sedentary or sluggish forms, such as Hemilepidotus hemilepidotus and family Tetraodontidae.[147] However, south of Alaska on the North American coast, fish are a negligible or extremely minor part of the sea otter's diet.[18][148] Contrary to popular depictions, sea otters rarely eat starfish, and any kelp that is consumed apparently passes through the sea otter's system undigested.[149]

The individuals within a particular area often differ in their foraging methods and prey types, and tend to follow the same patterns as their mothers.[150] The diet of local populations also changes over time, as sea otters can significantly deplete populations of highly preferred prey such as large sea urchins, and prey availability is also affected by other factors such as fishing by humans.[18] Sea otters can thoroughly remove abalone from an area except for specimens in deep rock crevices,[151] however, they never completely wipe out a prey species from an area.[152] A 2007 Californian study demonstrated, in areas where food was relatively scarce, a wider variety of prey was consumed. Surprisingly, though, the diets of individuals were more specialized in these areas than in areas where food was plentiful.[121]

As a keystone species

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Sea otters control herbivore populations, ensuring sufficient coverage of kelp in kelp forests

Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins, in check.[3] Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die.[153] Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens, with abundant sea urchins and no kelp forest.[5] Kelp forests are extremely productive ecosystems. Kelp forests sequester (absorb and capture) CO2 from the atmosphere through photosynthesis. Sea otters may help mitigate effects of climate change by their cascading trophic influence[154]

Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems,[155] and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California[156] However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors.[156] The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries.[156]

Sea otters affect rocky ecosystems that are dominated by mussel beds by removing mussels from rocks. This allows space for competing species and increases species diversity.[156]

Predators

Leading mammalian predators of this species include orcas and sea lions, and bald eagles may grab pups from the surface of the water. Young predators may kill an otter and not eat it.[62] On land, young sea otters may face attack from bears and coyotes. In California, great white sharks are their primary predator[157] but there is no evidence that the sharks eat them.

Urban runoff transporting cat feces into the ocean brings Toxoplasma gondii, an obligate parasite of felids, which has killed sea otters.[158] Parasitic infections of Sarcocystis neurona are also associated with human activity.[15] According to the U.S. Geological Survey and the CDC, northern sea otters off Washington have been infected with the H1N1 flu virus and "may be a newly identified animal host of influenza viruses".[159]

Relationship with humans

Fur trade

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Aleut men in Unalaska in 1896 used waterproof kayak gear and garments to hunt sea otters.

Sea otters have the thickest fur of any mammal, which makes them a common target for many hunters. Archaeological evidence indicates that for thousands of years, indigenous peoples have hunted sea otters for food and fur. Large-scale hunting, part of the Maritime Fur Trade, which would eventually kill approximately one million sea otters, began in the 18th century when hunters and traders began to arrive from all over the world to meet foreign demand for otter pelts, which were one of the world's most valuable types of fur.[21]

In the early 18th century, Russians began to hunt sea otters in the Kuril Islands[21] and sold them to the Chinese at Kyakhta. Russia was also exploring the far northern Pacific at this time, and sent Vitus Bering to map the Arctic coast and find routes from Siberia to North America. In 1741, on his second North Pacific voyage, Bering was shipwrecked off Bering Island in the Commander Islands, where he and many of his crew died. The surviving crew members, which included naturalist Georg Steller, discovered sea otters on the beaches of the island and spent the winter hunting sea otters and gambling with otter pelts. They returned to Siberia, having killed nearly 1,000 sea otters, and were able to command high prices for the pelts.[160] Thus began what is sometimes called the "Great Hunt", which would continue for another hundred years. The Russians found the sea otter far more valuable than the sable skins that had driven and paid for most of their expansion across Siberia. If the sea otter pelts brought back by Bering's survivors had been sold at Kyakhta prices they would have paid for one tenth the cost of Bering's expedition.[161] In 1775 at Okhotsk, sea otter pelts were worth 50–80 rubles as opposed to 2.5 rubles for sable.

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Pelt sales (in thousands) in the London fur market – the decline beginning in the 1880s reflects dwindling sea otter populations.[162]

Russian fur-hunting expeditions soon depleted the sea otter populations in the Commander Islands, and by 1745, they began to move on to the Aleutian Islands. The Russians initially traded with the Aleuts inhabitants of these islands for otter pelts, but later enslaved the Aleuts, taking women and children hostage and torturing and killing Aleut men to force them to hunt. Many Aleuts were either murdered by the Russians or died from diseases the hunters had introduced.[163] The Aleut population was reduced, by the Russians' own estimate, from 20,000 to 2,000.[164] By the 1760s, the Russians had reached Alaska. In 1799, Tsar Paul I consolidated the rival fur-hunting companies into the Russian-American Company, granting it an imperial charter and protection, and a monopoly over trade rights and territorial acquisition. Under Aleksander I, the administration of the merchant-controlled company was transferred to the Imperial Navy, largely due to the alarming reports by naval officers of native abuse; in 1818, the indigenous peoples of Alaska were granted civil rights equivalent to a townsman status in the Russian Empire.[165]

Other nations joined in the hunt in the south. Along the coasts of what is now Mexico and California, Spanish explorers bought sea otter pelts from Native Americans and sold them in Asia.[163] In 1778, British explorer Captain James Cook reached Vancouver Island and bought sea otter furs from the First Nations people. When Cook's ship later stopped at a Chinese port, the pelts rapidly sold at high prices, and were soon known as "soft gold". As word spread, people from all over Europe and North America began to arrive in the Pacific Northwest to trade for sea otter furs.[166]

Russian hunting expanded to the south, initiated by American ship captains, who subcontracted Russian supervisors and Aleut hunters[167] in what are now Washington, Oregon, and California. Between 1803 and 1846, 72 American ships were involved in the otter hunt in California, harvesting an estimated 40,000 skins and tails, compared to only 13 ships of the Russian-American Company, which reported 5,696 otter skins taken between 1806 and 1846.[168] In 1812, the Russians founded an agricultural settlement at what is now Fort Ross in northern California, as their southern headquarters.[166] Eventually, sea otter populations became so depleted, commercial hunting was no longer viable. It had stopped in the Aleutian Islands, by 1808, as a conservation measure imposed by the Russian-American Company. Further restrictions were ordered by the company in 1834.[169] When Russia sold Alaska to the United States in 1867, the Alaska population had recovered to over 100,000, but Americans resumed hunting and quickly extirpated the sea otter again.[170] Prices rose as the species became rare. During the 1880s, a pelt brought $105 to $165 in the London market, but by 1903, a pelt could be worth as much as $1,125.[74] In 1911, Russia, Japan, Great Britain (for Canada) and the United States signed the Treaty for the Preservation and Protection of Fur Seals, imposing a moratorium on the harvesting of sea otters.[171] So few remained, perhaps only 1,000–2,000 individuals in the wild, that many believed the species would become extinct.[18]

Recovery and conservation

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In the wake of the March 1989 Exxon Valdez oil spill, heavy sheens of oil covered large areas of Prince William Sound.

During the 20th century, sea otter numbers rebounded in about two-thirds of their historic range, a recovery considered one of the greatest successes in marine conservation.[172] However, the IUCN still lists the sea otter as an endangered species, and describes the significant threats to sea otters as oil pollution, predation by orcas, poaching, and conflicts with fisheries – sea otters can drown if entangled in fishing gear.[1] The hunting of sea otters is no longer legal except for limited harvests by indigenous peoples in the United States.[173] Poaching was a serious concern in the Russian Far East immediately after the collapse of the Soviet Union in 1991; however, it has declined significantly with stricter law enforcement and better economic conditions.[102]

The most significant threat to sea otters is oil spills,[62] to which they are particularly vulnerable, since they rely on their fur to keep warm. When their fur is soaked with oil, it loses its ability to retain air, and the animals can quickly die from hypothermia.[62] The liver, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming.[62] The Exxon Valdez oil spill of 24 March 1989 killed thousands of sea otters in Prince William Sound, and as of 2006, the lingering oil in the area continues to affect the population.[174] Describing the public sympathy for sea otters that developed from media coverage of the event, a U.S. Fish and Wildlife Service spokesperson wrote:

As a playful, photogenic, innocent bystander, the sea otter epitomized the role of victim ... cute and frolicsome sea otters suddenly in distress, oiled, frightened, and dying, in a losing battle with the oil.[18]

The small geographic ranges of the sea otter populations in California, Washington, and British Columbia mean a single major spill could be catastrophic for that state or province.[18][52][58] Prevention of oil spills and preparation to rescue otters if one happens is a major focus for conservation efforts. Increasing the size and range of sea otter populations would also reduce the risk of an oil spill wiping out a population.[18] However, because of the species' reputation for depleting shellfish resources, advocates for commercial, recreational, and subsistence shellfish harvesting have often opposed allowing the sea otter's range to increase, and there have even been instances of fishermen and others illegally killing them.[175]

In the Aleutian Islands, a massive and unexpected disappearance of sea otters has occurred in recent decades. In the 1980s, the area was home to an estimated 55,000 to 100,000 sea otters, but the population fell to around 6,000 animals by 2000.[176] The most widely accepted, but still controversial, hypothesis is that killer whales have been eating the otters. The pattern of disappearances is consistent with a rise in predation, but there has been no direct evidence of orcas preying on sea otters to any significant extent.[108]

Another area of concern is California, where recovery began to fluctuate or decline in the late 1990s.[177] Unusually high mortality rates amongst adult and subadult otters, particularly females, have been reported.[101] In 2017 the US Geological Survey found a 3% drop in the sea otter population of the California coast. This number still keeps them on track for removal from the endangered species list, although just barely.[178] Necropsies of dead sea otters indicate diseases, particularly Toxoplasma gondii and acanthocephalan parasite infections, are major causes of sea otter mortality in California.[179] The Toxoplasma gondii parasite, which is often fatal to sea otters, is carried by wild and domestic cats and may be transmitted by domestic cat droppings flushed into the ocean via sewage systems.[179][180] Although disease has clearly contributed to the deaths of many of California's sea otters, it is not known why the California population is apparently more affected by disease than populations in other areas.[179]

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Sea otters off the coast of Washington, within the Olympic Coast National Marine Sanctuary

Sea otter habitat is preserved through several protected areas in the United States, Russia and Canada. In marine protected areas, polluting activities such as dumping of waste and oil drilling are typically prohibited.[181] An estimated 1,200 sea otters live within the Monterey Bay National Marine Sanctuary, and more than 500 live within the Olympic Coast National Marine Sanctuary.[182][183]

Economic impact

Some of the sea otter's preferred prey species, particularly abalone, clams, and crabs, are also food sources for humans. In some areas, massive declines in shellfish harvests have been blamed on the sea otter, and intense public debate has taken place over how to manage the competition between sea otters and humans for seafood.[184]

The debate is complicated because sea otters have sometimes been held responsible for declines of shellfish stocks that were more likely caused by overfishing, disease, pollution, and seismic activity.[58][185] Shellfish declines have also occurred in many parts of the North American Pacific coast that do not have sea otters, and conservationists sometimes note the existence of large concentrations of shellfish on the coast is a recent development resulting from the fur trade's near-extirpation of the sea otter.[185] Although many factors affect shellfish stocks, sea otter predation can deplete a fishery to the point where it is no longer commercially viable.[184] Scientists agree that sea otters and abalone fisheries cannot exist in the same area,[184] and the same is likely true for certain other types of shellfish, as well.[176]

Many facets of the interaction between sea otters and the human economy are not as immediately felt. Sea otters have been credited with contributing to the kelp harvesting industry via their well-known role in controlling sea urchin populations; kelp is used in the production of diverse food and pharmaceutical products.[186] Although human divers harvest red sea urchins both for food and to protect the kelp, sea otters hunt more sea urchin species and are more consistently effective in controlling these populations.[187] The health of the kelp forest ecosystem is significant in nurturing populations of fish, including commercially important fish species.[186] In some areas, sea otters are popular tourist attractions, bringing visitors to local hotels, restaurants, and sea otter-watching expeditions.[186]

Roles in human cultures

AleutKalan1.jpg
Aleut carving of a sea otter hunt

Left: Aleut sea otter amulet in the form of a mother with pup. Above: Aleut carving of a sea otter hunt on a whalebone spear. Both items are on display at the Peter the Great Museum of Anthropology and Ethnography in St. Petersburg. Articles depicting sea otters were considered to have magical properties.[188]

For many maritime indigenous cultures throughout the North Pacific, especially the Ainu in the Kuril Islands, the Koryaks and Itelmen of Kamchatka, the Aleut in the Aleutian Islands, the Haida of Haida Gwaii[189] and a host of tribes on the Pacific coast of North America, the sea otter has played an important role as a cultural, as well as material, resource. In these cultures, many of which have strongly animist traditions full of legends and stories in which many aspects of the natural world are associated with spirits, the sea otter was considered particularly kin to humans. The Nuu-chah-nulth, Haida, and other First Nations of coastal British Columbia used the warm and luxurious pelts as chiefs' regalia. Sea otter pelts were given in potlatches to mark coming-of-age ceremonies, weddings, and funerals.[63] The Aleuts carved sea otter bones for use as ornaments and in games, and used powdered sea otter baculum as a medicine for fever.[190]

Among the Ainu, the otter is portrayed as an occasional messenger between humans and the creator.[191] The sea otter is a recurring figure in Ainu folklore. A major Ainu epic, the Kutune Shirka, tells the tale of wars and struggles over a golden sea otter. Versions of a widespread Aleut legend tell of lovers or despairing women who plunge into the sea and become otters.[192] These links have been associated with the many human-like behavioral features of the sea otter, including apparent playfulness, strong mother-pup bonds and tool use, yielding to ready anthropomorphism.[193] The beginning of commercial exploitation had a great impact on the human, as well as animal, populations the Ainu and Aleuts have been displaced or their numbers are dwindling, while the coastal tribes of North America, where the otter is in any case greatly depleted, no longer rely as intimately on sea mammals for survival.[194]

Since the mid-1970s, the beauty and charisma of the species have gained wide appreciation, and the sea otter has become an icon of environmental conservation.[177] The round, expressive face and soft, furry body of the sea otter are depicted in a wide variety of souvenirs, postcards, clothing, and stuffed toys.[195]

Aquariums and zoos

Sea otters can do well in captivity, and are featured in over 40 public aquariums and zoos.[196] The Seattle Aquarium became the first institution to raise sea otters from conception to adulthood with the birth of Tichuk in 1979, followed by three more pups in the early 1980s.[197] In 2007, a YouTube video of two sea otters holding paws drew 1.5 million viewers in two weeks, and had over 20 million views as of January 2015.[198] Filmed five years previously at the Vancouver Aquarium, it was YouTube's most popular animal video at the time, although it has since been surpassed. The lighter-colored otter in the video is Nyac, a survivor of the 1989 Exxon Valdez oil spill.[199] Nyac died in September 2008, at the age of 20.[200] Milo, the darker one, died of lymphoma in January 2012.[201]

See also

Notes

  1. ^ Enhydra lutris nereis is included in Appendix I

References

Citations

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Sea otter: Brief Summary

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The sea otter (Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg (31 and 99 lb), making them the heaviest members of the weasel family, but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.

The sea otter inhabits nearshore environments, where it dives to the sea floor to forage. It preys mostly on marine invertebrates such as sea urchins, various mollusks and crustaceans, and some species of fish. Its foraging and eating habits are noteworthy in several respects. Its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. In most of its range, it is a keystone species, controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems. Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries.

Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 1741 and 1911, and the world population fell to 1,000–2,000 individuals living in a fraction of their historic range. A subsequent international ban on hunting, sea otter conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species occupies about two-thirds of its former range. The recovery of the sea otter is considered an important success in marine conservation, although populations in the Aleutian Islands and California have recently declined or have plateaued at depressed levels. For these reasons, the sea otter remains classified as an endangered species.

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Loutre de mer

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Enhydra lutris

 src=
Une patte arrière, ayant évolué en nageoire.

La loutre de mer (Enhydra lutris) est une grande loutre (famille des mustélidés) vivant dans le Pacifique Nord, du nord du Japon (île de Hokkaidō) à la Californie, en passant par le Kamtchatka, les îles Aléoutiennes et l'Alaska. C'est la plus aquatique et la plus massive des loutres (elle peut atteindre jusqu'à 45 kg), mais aussi la seule à pouvoir vivre en permanence dans la mer.

La loutre de mer ne doit pas être confondue avec la loutre marine, Lontra felina, encore appelée chat de mer ou chungungo, qui vit le long des côtes du Pérou et du Chili et qui a besoin d'abris terrestres. Il arrive aussi quelquefois que certaines loutres d'eau douce, comme la loutre d'Europe, fassent des incursions en mer (le cas est même assez fréquent dans certains pays comme en Irlande), mais leur organisme n'est pas adapté à des séjours prolongés.

Les loutres de mer forment la seule espèce du genre Enhydra.

Chassées intensivement à compter de 1741 pour leur fourrure (la plus dense de tous les mammifères avec jusqu'à 170 000 poils par centimètre carré), les populations de loutre de mer ont été considérablement réduites, disparaissant même de nombreuses régions de leur zone de répartition historique. En 1911 on a estimé que leur population mondiale était tombée entre 1 000 et 2 000 individus. Bien que plusieurs sous-espèces soient encore en danger, les loutres marines, qui sont légalement protégées, ont vu leur population fortement augmenter. Les efforts de réintroduction ont également montré des résultats positifs.

Description physique

Les loutres de mer sont les plus lourdes des loutres (entre 25 et 30 kg), mais pas les plus grandes (entre 0,80 et 1,5 mètre)[1].

Avec leurs longs corps profilés, les loutres de mer sont adaptées à la vie en mer, une mer tempérée (Californie) à froide (Alaska, Kamtchatka) dont la température oscille souvent entre 1 et 13 °C seulement. La loutre a dû développer des adaptations très particulières pour survivre dans un tel milieu, en particulier au niveau de sa fourrure.

Celle-ci varie d'un brun rougeâtre au noir. Particulièrement dense (140 000 à 170 000 poils par centimètre carré), elle isole l'animal et maintient une couche d'air sous les poils, créant une barrière efficace entre l'eau et la peau. Le pelage comporte des poils longs, brillants, épais et résistants : les jarres. Il comporte aussi des poils courts, très denses, plus fins : la bourre. La loutre enduit ses poils avec la sécrétion de glandes cutanées huileuses, qui les imperméabilisent temporairement, et doit régulièrement être réappliquée. Le temps passé à imperméabiliser sa fourrure par la loutre de mer est de plusieurs heures par jour.
Le poil imperméabilisé (surtout la bourre), retient de nombreuses bulles d’air qui assurent l’isolation thermique (la peau reste plus ou moins sèche). Chez les jeunes, la quantité d’air est telle que ceux-ci ne peuvent ni plonger ni couler, ce qui est essentiel dans la mesure où ils ne savent pas nager à la naissance.

Les loutres ne possèdent pas de couche de graisse isolante comme les autres mammifères marins. L’eau provoquant une perte de chaleur 25 fois plus rapide que l’air, les animaux à sang chaud qui vivent dans l’eau doivent s’isoler, mais aussi produire plus de chaleur. L’isolation est fournie chez la loutre de mer par la fourrure, la production de chaleur par un métabolisme environ deux fois plus élevé que chez un mammifère terrestre de même taille. Ce métabolisme explique que la loutre de mer doive manger près de 25 % de son poids chaque jour pour maintenir sa température interne de 35 degrés Celsius (10 % seulement chez la loutre d'Europe, qui passe beaucoup moins de temps dans l’eau).

Il existe d'autres adaptations à la vie aquatique :

  • les narines et les oreilles se ferment hermétiquement pendant la plongée ;
  • l'apophyse épineuse (les « épines » qui sortent de la colonne vertébrale) est très développée, comme chez d’autres mammifères marins, ce qui offre un meilleur ancrage aux muscles du dos ;
  • la circulation sanguine a la particularité (dite rete mirabile)[2] d’être constituée (sous le derme) par un mélange de petites veines et de petites artères, les veines étant structurées pour bénéficier de la chaleur dégagée par les artères, ce qui réduit les pertes de chaleur ;
  • les poumons sont 2,5 fois plus larges que ceux d’un mammifère de même taille, pour favoriser les plongées (la loutre n’a en effet pas les couches de graisse épaisses des autres mammifères marins, qui leur servent à l’isolation thermique, mais aussi à stocker de l’oxygène pour les plongées) ;
  • le taux d’hémoglobine est plus important que chez un mammifère terrestre, facilitant le stockage de l’oxygène en plongée ;
  • le sang des loutres de mer a une grande capacité régulatrice qui aide ces animaux à supporter les excès de CO2 accumulés sous la pression durant la plongée ;
  • les naissances peuvent être reportées en cas de climat marin trop perturbé (voir le chapitre reproduction) ;
  • la lèvre supérieure, le nez et le dessus des yeux sont entourés de longues vibrisses (ressemblant aux « moustaches » des chats) qui repèrent les mouvements de l’eau, ce qui permet à l’animal de se diriger et de chasser dans des milieux aquatiques à faible visibilité ;
  • les yeux, les oreilles et les narines sont situés sur le dessus du crâne, comme chez beaucoup d’animaux aquatiques à respiration aérienne, ce qui permet à la loutre de rester dissimulée dans l’eau tout en respirant et en surveillant les alentours ;
  • les pattes avant ont des griffes rétractiles, alors que les pattes/nageoires postérieures sont plus longues, largement aplaties et palmées : ce sont surtout ces dernières qui servent à la propulsion.
  • Les reins sont plus gros que ceux des autres espèces de loutres, semble-t-il pour mieux éliminer l'accumulation de sel marin de l'organisme[3].

Sous chacune des puissantes pattes avant se trouve une poche de peau, employée pour stocker temporairement la nourriture ramassée pendant les plongées au fond, ou les pierres qu’elles utilisent volontiers comme outils[4].

Les loutres ont une queue assez courte, épaisse et musculeuse, qui leur sert de gouvernail.

Les loutres mâles peuvent atteindre un poids maximum de 45 kilogrammes et une longueur allant jusqu'à 1,5 mètre. La moyenne est cependant plutôt d'une trentaine de kilogrammes pour les mâles. Les femelles sont plus petites (un peu plus d'1 m), avec parfois seulement 70 cm, pour un poids moyen d’environ 23 kg.

Les femelles ont deux mamelles seulement.

Les deux canines supérieures sont très puissantes, et sensiblement plus grosses que les autres dents. Les deux canines inférieures sont également de bonnes tailles, mais plus petites. Les molaires sont robustes, sans doute une adaptation à une nourriture partiellement constituée d'animaux à coquilles ou carapaces[5].

Les loutres mènent des vies relativement longues : jusqu'à 23 ans dans la nature[6] (quinze - vingt ans en moyenne).

Comportement et reproduction

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Les loutres de mer sont des animaux sociaux.

Les loutres de mer peuvent être solitaires ou vivre en groupes. Ces animaux sont en général plutôt sociaux, et on a relevé en Alaska des groupes comptant jusqu’à 2 000 individus. En Californie, où la population est moins importante, les groupes font plutôt de 10 à 100 individus. Les groupes sont souvent sexuellement séparés, les groupes de mâles étant en général plus importants que ceux des femelles.

En surface, les loutres de mer nagent souvent sur le dos. On peut supposer qu’il s’agit d’une adaptation à la vie en eau froide. Cette position permet de maintenir le bout du museau et les pattes hors de l’eau. Ces zones du corps sont en effet dépourvues de fourrure (mais ne représentent qu’1 % de la surface corporelle). Les loutres passent en posture ventrale quand elles souhaitent nager plus vite, par exemple en situation de fuite. Elles se reposent sur le dos en s'enroulant dans les frondes géantes du kelp, ce qui leur évite de dériver pendant qu'elles mangent ou pendant leur sommeil.

Les femelles ont une durée de vie plus importante que celle des mâles, avec 15 à 20 ans d'espérance de vie[7], tandis que les mâles ne vivent que de 10 à 15 ans[3].

Les loutres de mer dorment sur le dos dans l'eau. En groupe, elles se donnent souvent la main en dormant pour ne pas dériver et rester ensemble[8].

Les forêts de kelp

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Une forêt de kelp à l'aquarium californien de Monterey.

Les forêts de kelp sont de véritables forêts d'algues géantes formant le kelp et pouvant mesurer plus de 30 m de long. Ces algues sont ancrées sur le sol et flottent jusqu'à la surface grâce aux flotteurs qui se trouvent à la base des feuilles. Ces forêts sont un habitat privilégié pour les loutres de mer grâce à l’ancrage qu'elles fournissent (les loutres s'enveloppent dans les feuilles flottant en surface), les protégeant des tempêtes et des courants et grâce à l'abondance de la nourriture qui s'y trouve. Cependant, les loutres de mer ne sont pas strictement inféodées aux forêts de kelp, et certains groupes vivent dans des zones sans kelp.

On a montré que la loutre de mer avait un impact favorable sur l’extension des forêts de kelp : les loutres mangent énormément d’oursins, qui sont des brouteurs de kelp. Là où les loutres reviennent, le kelp se porte mieux et ses forêts se développent, permettant à toutes sortes d’animaux (invertébrés mais aussi poissons) de s’y développer. Là où les loutres sont absentes, les forêts de kelp sont dégradées et plus restreintes[9].

Cette action sur le kelp peut d’ailleurs jouer en faveur des loutres. Les pêcheurs californiens d’ormeaux ont en effet longtemps considéré les loutres comme des concurrentes, car les loutres sont des prédateurs des ormeaux. Bien qu’interdit, les tirs des loutres par ces pêcheurs ne sont donc pas rares. Mais les ormeaux dépendent des forêts de kelp ou ils vivent, forêts que les loutres contribuent à étendre. Les loutres ont donc un impact positif à long terme sur les populations d'ormeaux. Certains espèrent que la découverte de cet impact positif contribuera à détendre l’atmosphère entre pêcheurs californiens et loutres.

Déplacements et recherche de nourriture

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Des goélands guettent les reliefs du repas de cette loutre.
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En train de dormir.

La loutre de mer vient à terre là où cela est possible, surtout pour se protéger des tempêtes, mais n'en a pas vraiment besoin, pas même pour la reproduction, qui est largement aquatique, de la conception à la naissance (voir le chapitre reproduction). Près des zones très habitées (comme en Californie), certaines populations de loutres ne viennent jamais ou presque jamais à terre.

Les données contradictoires concernant les déplacements des loutres de mer suggèrent que ceux-ci (ou leur absence) dépendent de la disponibilité des ressources alimentaires. Elles ne bougent généralement que de 1 à 2 km par jour, et ont des territoires qui peuvent dépasser 5 km².

La loutre de mer est un animal diurne. La majeure partie de sa journée est consacrée au toilettage et à la recherche de nourriture.

Le toilettage est essentiel : dépourvue de graisse isolante, la loutre de mer dépend pour sa survie de la protection offerte par sa fourrure. Celle-ci doit être régulièrement nettoyée et graissée (voir le chapitre description physique) pour conserver son efficacité, sous peine d'hypothermie.

La recherche de nourriture est plus intense le matin et le soir (alimentation crépusculaire).

La loutre prélève ses proies sur le fond de la mer. Les plongées sont assez courtes, ne durant généralement pas plus de 90 secondes, mais elles peuvent atteindre 4 ou 5 minutes.

La nourriture est largement constituée de diverses espèces de bivalves, d’escargots, de chitons, de crabes, d’étoiles de mer, d'oursins et même parfois de poissons[10]. Il y a semble-t-il des variations géographiques dans le régime de l'animal. Si les poissons semblent un apport relativement marginal dans les eaux nord-américaines, ils seraient au contraire importants « dans certaines parties des îles Aléoutiennes et du Commandeur ainsi que dans les Kouriles[11] »

Dans les eaux obscures ou sales, elle détecte ses proies à l'aide de vibrisses, moustaches sensibles qui ornent ses joues.

Du fait de cette nourriture, qui vit essentiellement sur le fond, la loutre de mer n'a pas vraiment de saison de reproduction, mais on note des pointes entre mai et juin dans les populations nordiques, et entre janvier et mars dans les populations méridionales.

Les femelles adultes lavent et (au besoin) ouvrent leurs proies avec une roche qu'elles gardent dans leur poche. La roche peut être utilisée comme enclume : l'animal fait la planche, pose la pierre sur son ventre, et frappe le coquillage dessus. Elle peut aussi être utilisée comme marteau. Les loutres de mer présentent ainsi un exemple d'utilisation d'outil par un mammifère non humain[12],[13].

Reproduction

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Une mère et son petit.

Il n'y a pas vraiment de saison de reproduction, mais on note des pointes entre mai et juin dans les populations nordiques, et entre janvier et mars dans les populations méridionales.

Les mâles ont des partenaires féminines multiples, mais sans vie commune. Les mâles et les femelles se rapprochent pendant les chaleurs de la femelle. Les femelles évitent les mâles en dehors de cette période. Durant la période des chaleurs, les mâles défendent leurs territoires ; il n'y a que très rarement des combats réels, la plupart des conflits se réglant par intimidation. Les femelles adultes ont des cicatrices caractéristiques de l'habitude qu'ont les mâles de leur tenir la tête entre leurs mâchoires pendant la reproduction.
Quand les mâles et les femelles se font la cour, ils nagent rapidement et plongent ensemble, le mâle faisant des tire-bouchons dans l'eau. Pendant l'accouplement, le mâle mord la femelle sur la nuque, le cou ou le nez, lui laissant des cicatrices.

La gestation est de 4 à 6 mois[14], bien qu'elle puisse être prolongée de plusieurs jours à une année si l'œuf fertilisé ne s'enfonce pas immédiatement dans la paroi utérine. Pendant cette période de suspension, l'œuf ne se développe pas. Ceci se produit en particulier quand l'agitation de la mer (tempêtes) perturbe l'implantation. Il s'agit sans doute d'une adaptation qui optimise la reproduction et la protection des jeunes dans le milieu rude d'un océan froid aux tempêtes fréquentes.

La gestation finit habituellement par une naissance simple. Les jumeaux sont une rareté, et habituellement seul l'un d'entre eux survit. Les nouveau-nés font 1,5 à 2,3 kg, ont les yeux ouverts et une fourrure déjà épaisse, pour flotter et survivre dans l'eau froide. La grosse taille des petits est tout à fait inhabituelle chez un mustélidé. D'après James Bodkin et Daniel Monson, de l’Alaska Science Center[15], cette taille importante est une adaptation aux rigueurs de la vie océanique. Ils notent à ce propos que le rapport entre le poids de la mère et celle du petit Enhydra lutris est beaucoup plus proche de celui existant chez les pinnipèdes que chez les mustélidés en général.

Les naissances peuvent se faire à terre avec transport rapide des jeunes vers l'eau, ou directement en mer. Le nombre des naissances en mer serait plus important chez les loutres de Californie (même si on y trouve des naissances terrestres d'après R. J. Jameson)[16] que chez les 2 sous-espèces nordiques.

En cas de décès du petit, la femelle entre souvent en chaleur dans les jours qui suivent, et retombe enceinte presque aussitôt. Les décès des petits étant plus fréquents l'hiver, compte tenu des conditions climatiques, cette particularité assure une naissance à un moment statistiquement plus favorable, c’est-à-dire le printemps ou l'été.

Les petits peuvent assimiler de la nourriture solide très peu de temps après leur naissance. Ils sont jaune brunâtre, et restent en permanence près de la mère, dont ils sont dépendants six mois ou plus. La mère enseigne aux petits comment chasser, plonger, et se toiletter efficacement. Elle a en général un petit tous les ans ou tous les deux ans. Ceux-ci commencent à plonger vers l'âge de 2 mois. Ils restent avec la mère 5 à 8 mois après la naissance[17].

La plupart des femelles sont sexuellement matures vers trois ou quatre ans, parfois même deux ans : « Une petite proportion des femelles a son premier petit à 2 ans, environ 50 % se reproduisent pour la première fois à l'âge de trois ans, et la plupart des femelles ont eu un petit à l'âge de 4 ans »[15].
Les mâles se reproduisent rarement avant 5-6 ans, bien que la maturité sexuelle physique puisse être atteinte plus tôt[3].

Taxinomie et systématique

L'espèce Enhydra lutris a été décrite pour la première fois en 1758 par le naturaliste suédois Carl von Linné (1707-1778) et le genre monotypique Enhydra en 1822 par le zoologiste et géologue écossais John Fleming (1785-1857).

Les auteurs identifient traditionnellement trois sous-espèces.

Liste de genre, espèce et sous-espèces

Selon Mammal Species of the World (version 3, 2005) (22 mai 2013)[18], Catalogue of Life (22 mai 2013)[19] et World Register of Marine Species (22 mai 2013)[20] :

  • Enhydra Fleming, 1822
    • Enhydra lutris (Linnaeus, 1758)
      • sous-espèce Enhydra lutris kenyoni Wilson, 1991
      • sous-espèce Enhydra lutris lutris (Linnaeus, 1758)
      • sous-espèce Enhydra lutris nereis (Merriam, 1904)

La destruction de la loutre

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La vente de peaux à Londres, et son effondrement final. Le nombre de peaux est exprimé en milliers.

L’habitat de la loutre de mer allait à l’origine du nord du Japon (Hokkaidō) au nord du Mexique (péninsule de Basse-Californie), en suivant la cote nord-asiatique, les îles Aléoutiennes puis la cote pacifique de l’Amérique du Nord.

La population originelle comptait sans doute des centaines de milliers d’individus (de 150 000 à un million, selon les estimations). Le nombre des sous-espèces est difficile à déterminer, mais il y en a trois aujourd’hui. Eu égard à l’importance de la destruction des populations, il est possible que certaines sous-espèces aient disparu avant d’avoir été décrites.

Les populations de son aire de répartition pratiquaient une chasse traditionnelle, qui est attestée archéologiquement, et a peut-être entraîné des disparitions locales anciennes[11]. C'est cependant la grande chasse qui s'organise entre 1741 et 1911 qui entraînera la quasi-disparition de l'espèce.

Aux XVIIe et XVIIIe siècles, la Russie a été fortement impliquée dans le commerce de la fourrure de zibeline. Le tsar Pierre le Grand souhaitait développer cette activité économique, et trouver de nouvelles populations à chasser. Les chasseurs russes s’installèrent donc de plus en plus loin en Sibérie, jusqu’au Kamtchatka, presqu’île riche en zibeline, mais où on trouvait aussi des loutres de mer.

En 1741 et 1742, Vitus Béring et Alexei I. Chirikov furent chargés par le gouvernement russe d’explorer le Pacifique nord et de tracer une route maritime vers l’Amérique à partir des nouvelles possessions russes d’Extrême-Orient. Lors de leur hivernage de 1741-1742, les équipages récoltèrent des peaux de loutre. En 1742, les survivants de l’expédition (Bering était mort) revinrent en Russie avec 900 peaux de loutres, qui intéressèrent vivement les marchands de fourrure. Avec près de 170 000 poils par cm², la fourrure de loutre de mer est en effet particulièrement dense et soyeuse. Ce fut le début de la grande chasse.

Les Russes envoyèrent de nombreux bateaux chasser la fourrure de loutre. Après l’épuisement des populations nord-asiatiques de loutres, la prise des îles Aléoutiennes puis de l’Alaska par la Russie fut largement motivée par la volonté d’étendre les territoires de chasse à la loutre, devenue une activité particulièrement rentable.

En 1784, les Russes établirent des comptoirs de traite sur les îles Aléoutiennes et sur la côte de l'Amérique, en Alaska. Des postes côtiers furent construits à Attu, Agattu et Unalaska, dans les îles Aléoutiennes, ainsi que dans l'île de Kodiak, au large de l'embouchure de l'anse Cook (Alaska). Dix-huit mois plus tard, une colonie fut établie sur le continent, en face de l'anse Cook.

Les populations indigènes furent souvent férocement traitées. Des Aléoutes furent réduits en esclavage, et d’autres auraient été pris en otages pour forcer la population indigène à chasser la loutre pour le compte des marchands russes. On comptait environ 25 000 Aléoutes avant l’arrivée des Russes, mais ils n’étaient plus que 3 892 en 1885[21].

La fourrure de loutre se vendait non seulement en Europe, mais aussi à prix d'or sur les marchés chinois.

Si les Russes furent les premiers à industrialiser la chasse, les Britanniques puis les Américains les suivirent rapidement. En 1776, le capitaine James Cook explora le Pacifique nord pour le compte de la Grande-Bretagne. C’est lors de cette expédition que la fourrure de loutre fut identifiée par les Britanniques comme un commerce à fort potentiel, attirant dès la fin du XVIIIe siècle de nouveaux chasseurs dans la région, en particulier Britanniques, Espagnols puis Américains.

Rien qu'entre 1785 et 1809, 55 000 peaux furent débarquées en Colombie-Britannique par les navires de chasse ou les marchands, en provenance de diverses régions d'Amérique du Nord[11].

« En 1850, la loutre de mer canadienne était considérée comme disparue sur le plan commercial et était peut-être déjà disparue sur le plan écologique[11] ». Quelques loutres subsistaient au Canada (la dernière recensée y sera tuée en 1929[11]), mais sans impact environnemental.

L'Alaska ayant également été presque totalement vidé de ses populations de loutres de mer, la région devint économiquement peu intéressante pour le gouvernement russe, amenant celui-ci à vendre ce territoire et les Aléoutiennes aux États-Unis en 1867.

Vers la fin du XIXe siècle, la chasse cessa d’être rentable. Les populations de loutre avaient presque totalement disparu. La dernière loutre connue de l'État américain de l'Oregon fut ainsi tuée en 1906. Les expéditions de chasse ne pouvaient plus ramener assez de peaux pour se financer.

Seules quelques petites populations résiduelles et très fragmentées avaient survécu. « On estime que seulement 2 000 individus, soit plus ou moins 1 % de la population initiale, auraient survécu dans les 13 populations qui subsistaient en 1911[11] ». Certaines de ces 13 populations, trop petites ou victimes de braconnages, finiront d'ailleurs par disparaître, comme celle des îles de la Reine-Charlotte[22].

Protection

La pression des marchands de fourrure ayant disparu avec l’intérêt commercial de la chasse, la loutre de mer fut protégée en 1911 par le « traité international sur le phoque à fourrure », ratifié par les États-Unis, la Russie, le Japon et la Grande-Bretagne (pour le Canada[11]), à un moment où beaucoup pensaient qu’elle était déjà condamnée. Ce traité était un des premiers à organiser une protection d'espèce au niveau international[23].

Les survivants

Bien que la chasse de loutre ait été officiellement interdite, et que les animaux soient devenus très difficiles à trouver, des braconniers ont continué à les chasser.

Ainsi, « la dernière loutre de mer dont la prise a été confirmée au Canada a été abattue en 1929 près de Kyuquot, en Colombie-Britannique[11] ».

Les braconniers japonais étaient également sur le point d'éliminer totalement les loutres restantes dans les îles Aléoutiennes (possession américaine depuis 1867) lors du déclenchement de la Seconde Guerre mondiale. La zone fut militarisée par les deux parties. Il y eut une occupation partielle des îles par le Japon et le renforcement de la présence militaire américaine dans le reste de la zone. Du fait de cette militarisation et des dangers liés à l'état de guerre, le braconnage cessa.

Avec le groupe des Aléoutiennes, d’autres petites populations ont survécu de justesse, en particulier en Alaska ou au Kamtchatka. Un groupe a été identifié au large de Carmel, en Californie en 1938, dans une zone où on pensait que les loutres avaient totalement disparu. Une estimation de 1976 considère qu'il devait y avoir une cinquantaine de survivants de E. lutris nereis vers 1914[24]. D'autres estimations parlent de 10 à 30 survivants seulement.

Ces différents survivants ont permis aux 3 sous-espèces de se reconstituer naturellement, colonisant progressivement les zones se trouvant autour d'eux.

Un exemple de recolonisation ayant été assez largement étudié est celui d'Enhydra lutris nereis, la sous-espèce californienne :

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Recolonisation de la côte californienne par Enhydra lutris nereis entre 1938 et 1998.
Enhydra lutris californie demographie.jpg
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Fortement peuplée, la Californie entraîne des cohabitations forcées.

Réintroductions

En plus de la croissance naturelle des populations, des réintroductions couronnées de succès ont été réalisées le long des côtes nord-américaines pour accélérer la recolonisation, en particulier au Sud-Est de l'Alaska, dans l’État de Washington (États-Unis) et en Colombie-Britannique (Canada).

Par exemple, 89 loutres de mer d’Alaska (« provenant de l’île Amchitka et du détroit du Prince William[11] ») ont été introduites en plusieurs étapes en Colombie-Britannique en 1969 et 1972, « dans la baie Checleset, sur la côte ouest de l’île de Vancouver[11] ». Comme souvent, la translocation a entraîné une surmortalité, et la population a rapidement diminué, peut-être jusqu'à seulement 28 individus[25]. Cette petite population s'est ensuite adaptée, et a dès lors rapidement augmenté, puisqu’elle atteignait déjà 1 500 individus en 1995 et 3 185 en 2004[11].

Ainsi aussi, 59 loutres des Aléoutiennes ont été implantées en 1969 et 1970 dans les eaux de l’État de Washington (États-Unis). Après un démarrage assez lent (100 animaux en 1987), une enquête de 2001 en recensait 555[26], et 814 en 2005[27].

Des réintroductions de loutre d'Alaska dans le sud-est de l'Alaska ont également réussi, les autorités ayant déplacé entre 1965 et 1969 412 loutres provenant du sud-ouest de l’Alaska[28].

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La réintroduction des loutres de Californie sur l'Île San Nicolas.

Certaines réintroductions, ont par contre échoué, ou ont connu des succès partiels. C'est ainsi qu'une population de 140 membres de la sous-espèce Enhydra lutris nereis a été installée entre 1987 et 1990 autour de l'Île San Nicolas, en face de Los Angeles, un peu au sud de la zone recolonisée naturellement par la loutre de Californie. Le succès a été très partiel, la population peinant à se développer vraiment. Cet échec partiel est sans doute en partie le fait de la stratégie choisie. En effet, devant l'opposition des pécheurs, une « zone exempte de loutres de mer » a été instituée au sud de la pointe conception, la limite sud de recolonisation naturelle par les loutres. Les animaux entrant dans cette zone (dont la seule exception était l'île San Nicolas) devaient être capturés et ramenés dans la zone réservée, au nord. « En juillet 2000, le USFWS[29] a décidé que le confinement des loutres de mer en tentant de maintenir la zone exempte de loutres de mer mettait en péril le rétablissement de la population de loutres de mer du Sud et a arrêté de retirer les loutres de mer présentes dans la zone d’exclusion[11] ». Cette nouvelle politique devrait favoriser la descente des populations du nord vers Los Angeles, et sécuriser la population de San Nicolas. Mais le développement à long terme de cette nouvelle population reste en 2007 incertain.

De son côté, la réintroduction de population dans l'Oregon a été un échec total[28].

La situation des différentes sous-espèces

Enhydra-lutris.jpg

Il y a aujourd’hui 3 sous-espèces reconnues (voir Wilson sur l'histoire de la taxonomie de l'espèce - 1991) :

  • La loutre de mer d’Asie (Enhydra lutris lutris ou E. l. gracilis, selon les classifications) est la plus petite. Elle vit sur la côte ouest du Kamtchatka (fédération de Russie) et autour des Îles Kouriles. Elles seraient entre 15 et 20 000 en 2006. Cette sous-espèce a totalement disparu du Japon, mais une recolonisation à partir des Kouriles est possible, et l'observation d'au moins un individu en 1997 a été rapportée par Gorbics[30].
  • La loutre de mer d’Alaska (Enhydra lutris kenyoni ou E. l. lutris, selon les classifications), vit sur les îles Aléoutiennes, sur les côtes de l’Alaska. Des groupes ont été réintroduits en Colombie-Britannique (Canada) et dans l'État de Washington (États-Unis). Elles seraient en 2006 une centaine de milliers, surtout présentes en Alaska. La population des Aléoutiennes semble en forte baisse, et le Pages liées à Center for Biological Diversity a demandé en 2000 un statut de protection renforcé[31].
  • La loutre de mer de Californie (Enhydra lutris nereis) est la moins nombreuse. Elle a une taille intermédiaire entre E. l. gracilis et E. l. lutris. À l’origine, on la trouvait sur toutes les côtes du sud-ouest de l’Amérique du Nord. Déjà rare dès 1830, elle était exterminée au début du XXe siècle. Seules quelques dizaines d’animaux ont survécu près de Carmel en Californie, à mi-chemin entre Los Angeles (au sud) et San Francisco (au nord). Limité à une petite zone autour de Big Sur (Carmel), l'animal s'est progressivement développé jusqu'à coloniser presque tout le territoire entre les deux grandes métropoles californiennes (voir ci-dessus pour une carte de ce développement). Ils seraient en 2006 2 800 animaux sur 400 km de côte.

« Une analyse génétique récente indique [...] qu’un certain flux génétique s’est produit entre les individus de la Californie et du détroit du Prince-William, en Alaska, avant la traite des fourrures marines[32] ». La séparation entre les sous-espèces, ici Enhydra lutris nereis et Enhydra lutris kenyoni n'empêche donc pas des croisements ponctuels.

Il existe un problème de nom, puisque certains scientifiques appellent la sous-espèce asiatique Enhydra lutris lutris (et non Enhydra lutris gracilis), et la sous-espèce aléouto-alaskane Enhydra lutris kenyoni (et non Enhydra lutris lutris).

Protections légales

Les loutres sont aujourd’hui présentes dans la quasi-totalité de leur ancienne zone de présence, mais de façon beaucoup moins dense, avec un habitat en taches de léopard. En pratique, seule la moitié des eaux où elles habitaient ont actuellement une présence de loutres, et la sous-espèce de Californie reste fortement menacée.

Aujourd'hui, les différentes populations sont stables, en lente augmentation ou en régression (selon les zones). La tendance globale en 2007 semble être une lente augmentation. Là ou des régressions sont constatées, une des hypothèses avancées est celle d'une prédation beaucoup plus forte des orques[33], ainsi que diverses menaces humaines.

Malgré son retour relatif, la loutre de mer est toujours protégée. Elle l’est au niveau international (la CITES a placé la sous-espèce de Californie (E. lutris nereis) en annexe I : protection maximale, et les 2 autres sous-espèces en annexe II), mais aussi par des lois des pays concernés, comme la Loi sur les espèces en péril et la Loi sur les pêches du Canada[11] ou l'U.S. Marine Mammal Protection Act de 1972 aux États-Unis.

Au Canada, la loutre de mer était « désignée comme étant « en voie de disparition » en avril 1978[11] », un statut confirmé en 1986. L'animal a obtenu un « réexamen du statut et [une] désignation en tant qu’espèce « menacée » en avril 1996 et en mai 2000[11] ». « Le Comité sur la situation des espèces en péril au Canada (COSEPAC) a procédé, en avril 2007, à la réévaluation de la situation de la population de loutres de mer et l’a désignée en tant qu’espèce préoccupante [...] du fait qu’elle avait repeuplé de 25 à 33 % de son aire de répartition historique et que la population est en croissance et en expansion. Toutefois, on considère que l’effectif demeure peu élevé ([11] ».

Prédateurs et menaces

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Les marées noires sont l'une des causes de mortalité non-naturelle des loutres de mer (ici en Alaska)

Causes naturelles

Les prédateurs naturels[34],[35] de la loutre sont les orques (ou épaulards), les requins, mais aussi certains oiseaux, comme le pygargue (qui s’attaque surtout aux jeunes), voire exceptionnellement des prédateurs terrestres, comme le coyote (quand elles viennent à terre).

« Les épaulards ne seraient pas une cause de mortalité importante en Colombie-Britannique [...]. Par contre, la prédation par les épaulards peut être importante dans l’ouest de l’Alaska, où des déclins spectaculaires touchent présentement la population de loutres de mer[35] avancent l’hypothèse que, en raison des déclins spectaculaires dans les populations de phoques et de lions de mer résultant d’un changement à grande échelle au niveau de l’écosystème, les épaulards s’alimentant de mammifères auraient commencé à s’attaquer aux loutres de mer et seraient la cause du déclin observé dans la population de celles-ci. La prédation par le grand requin blanc est une cause importante de mortalité chez les loutres de mer du Sud [en Californie] et s’est accrue au fil du temps, particulièrement pendant la période de déclin récent et actuel touchant cette population de loutres de mer[36] »[11].

Les tempêtes et le manque de nourriture peuvent aussi causer des pertes importantes au sein des groupes.

Causes artificielles

Dans certaines zones, la pollution et les filets des pêcheurs (prises accidentelles) représentent un risque important. On estime que la marée noire de l’Exxon Valdez, en Alaska en 1989, a tué environ 800 à 5 000 loutres (selon les estimations).

Chez les loutres de Californie, le problème vient d'une proximité très forte avec les humains, les côtes de la Californie étant particulièrement peuplées. « Au milieu des années 1970, on a décelé un déclin d’environ 5 % par année, lequel a été attribué à des mortalités provoquées par les filets de pêche submergés. La tendance s’est inversée à la suite de l’imposition de restrictions sur l’utilisation des filets et, en 1995, les relevés indiquaient une population d’au moins 2 377 individus[11] ». Bien que la tendance, soit actuellement satisfaisante, on a cependant noté une forte mortalité chez les loutres de Californie du fait de maladies infectieuses ou parasitaires favorisées par la pollution. De fait, des études ont montré une contamination notable par des pesticides organochlorés chez des animaux retrouvés morts le long de la côte de Californie[37]. « en général, on ne croit pas que les maladies soient une cause de mortalité importante dans la plupart des populations de loutres de mer, excepté celles de la Californie. En Californie, les maladies sont en effet responsables de 40 % mortalités d’individus dont les carcasses ont été retrouvées sur les plages et contribuent à maintenir un faible taux de croissance démographique, comparativement à d’autres populations de loutres de mer[11] ».

Dans les eaux territoriales russes (Kouriles et Kamtchatka), « la population est menacée par le braconnage, la contamination de l’habitat et les conflits avec les pêches. Le braconnage est particulièrement important du fait que l’on croit qu’un marché noir existe en Russie et qu’il permet d’exporter illégalement des fourrures vers la Chine, la Corée et le Japon (Burdin[38], 2000)[11] ».

Dans l'océan Arctique, le déclin de la glace dû au réchauffement climatique et à la formation des voies de navigation maritimes menace[39] les populations d'Enhydra lutris kenyoni. Le remodelage radical des glaces aurait permis le contact, auparavant impossible, entre différentes espèces de phoques, dont une partie était infectée par le virus Phocine morbillivirus. Ce dernier est responsable d’une épidémie de la maladie de Carré des phoques ayant entraîné la mort de milliers de phoques dans l’Atlantique Nord en 2002[40],[41] et a également été relevé chez la loutre de mer en Alaska[42]. La disparition des glaces pousse la faune marine à se déplacer et s’alimenter dans de nouveaux habitats, ce qui la rend susceptible de contracter de nouvelles maladies infectieuses. C'est ainsi que le virus s’est introduit dans le nord de l’océan Pacifique et a pu contaminer les espèces le peuplant.

Conséquences

Les menaces actuellement enregistrées n'empêche pas la population des loutres de mer d'être en lente augmentation, mais cette augmentation ne vaut pas pour toutes les zones, et certaines connaissent des baisses de populations.

La diminution la plus spectaculaire est celle des loutres des Aléoutiennes. Alors que les autres populations sont plus ou moins en expansion, la population des Aléoutiennes s'est effondrée, passant d'un fourchette entre 55 et 73 000 individus en 1985 à moins de 9 000 animaux en 2000[11]. Cet effondrement est mal compris, mais l'hypothèse d'une prédation croissante par les orques est souvent avancée, sans preuve formelle.

Estimation de populations

La compilation des estimations des populations locales est difficile, sachant que les méthodes utilisées sont différentes selon les équipes scientifiques, et que les années d'observation ne sont pas les mêmes.

La principale différence vient de l'utilisation de la méthode du comptage des seuls animaux vus, ou de la méthode du comptage estimé, qui ajoute aux animaux observés une hypothèse sur une proportion d'animaux non observés.

Le total des estimations ci-dessous peut-être considéré comme un minimum, beaucoup de ces estimations ne reposant que sur les observations directes, lesquelles ne peuvent espérer être exhaustives. Le total des animaux vivants en 2007 peut donc être estimé entre 100 000 et 150 000 bêtes.

(a) Comptage direct des seuls animaux observés.
(b) Estimations corrigées en fonction des animaux non observés.

Voir aussi

Bases de référence taxonomiques

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Loutre de mer: Brief Summary

provided by wikipedia FR

Enhydra lutris

 src= Une patte arrière, ayant évolué en nageoire.

La loutre de mer (Enhydra lutris) est une grande loutre (famille des mustélidés) vivant dans le Pacifique Nord, du nord du Japon (île de Hokkaidō) à la Californie, en passant par le Kamtchatka, les îles Aléoutiennes et l'Alaska. C'est la plus aquatique et la plus massive des loutres (elle peut atteindre jusqu'à 45 kg), mais aussi la seule à pouvoir vivre en permanence dans la mer.

La loutre de mer ne doit pas être confondue avec la loutre marine, Lontra felina, encore appelée chat de mer ou chungungo, qui vit le long des côtes du Pérou et du Chili et qui a besoin d'abris terrestres. Il arrive aussi quelquefois que certaines loutres d'eau douce, comme la loutre d'Europe, fassent des incursions en mer (le cas est même assez fréquent dans certains pays comme en Irlande), mais leur organisme n'est pas adapté à des séjours prolongés.

Les loutres de mer forment la seule espèce du genre Enhydra.

Chassées intensivement à compter de 1741 pour leur fourrure (la plus dense de tous les mammifères avec jusqu'à 170 000 poils par centimètre carré), les populations de loutre de mer ont été considérablement réduites, disparaissant même de nombreuses régions de leur zone de répartition historique. En 1911 on a estimé que leur population mondiale était tombée entre 1 000 et 2 000 individus. Bien que plusieurs sous-espèces soient encore en danger, les loutres marines, qui sont légalement protégées, ont vu leur population fortement augmenter. Les efforts de réintroduction ont également montré des résultats positifs.

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해달

provided by wikipedia 한국어 위키백과

해달(한국 한자: 海獺, 학명: Enhydra lutris, sea otter)은 북태평양 북안과 동안에 서식하는 해양 포유류이다.[2] 다 자란 해달의 몸무게는 14-45Kg이며, 이는 족제빗과의 종 중 아주 무거운 편이지만 해양 포유류에 비할 수 없을 만큼 가볍다. 다른 해양 포유류와는 달리 해달의 보온장치는 지방질이 아니라 매우 두꺼운 털가죽이다. 땅에서 걸을 수 있지만 땅을 한 번도 밟지 않고 일생을 보내는 것이 가능하다.

해달은 해안지역에 서식하며 먹이를 위해서는 해면으로 잠수한다. 주식은 성게, 연체동물, 갑각류, 물고기 등이다. 이들의 식성과 먹는 방식은 여러 방면에서 특이하다. 우선 도구를 사용하는 몇 안 되는 동물이라는 점인데 바위를 이용해 조개 등을 깨는 습성에서 볼 수 있다. 서식지에서 해달은 성게 수를 조절하는 데에 중요한 역할을 하며, 이들의 숫자가 줄면 해초 숲이 성게에 의해 초토화될 수도 있다. 해달의 식단 중 인간이 섭취하는 종도 있으므로 어부와의 충돌이 일어나기도 한다.

해달의 개체 수는 털을 위한 남획 전 15만 마리에서 30만 마리였지만 1741년1911년 사이에 이루어진 사냥 때문에 개체 수가 1,000 ~ 2,000마리로 줄었으며 분포지역 또한 줄어들게 되었다. 국제적으로 사냥을 금지하고 재도입 계획으로 개체 수는 늘어나 이제는 한때 차지하던 서식지의 66%를 차지하고 있다. 해달의 회복은 종의 회복에 관한 예를 들 때 캘리포니아의 귀신고래와 함께 성공 사례로 거론된다. 하지만 알류샨 열도캘리포니아의 해달 개체군은 감소하는 등 아직도 위험에 놓여 있다. 이러한 이유로 해달은 여전히 멸종 위기종으로 분류되고 있다.

생물 분류

 src=
캘리포니아 모로베이의 해달 가족. 매우 드물게도 새끼가 쌍둥이이다.

해달의 쌍둥이는 매우 드물게 태어나며, 태어나도 어미가 두 마리를 모두 키울 여력이 없어 대개 한 마리를 버리게 된다.[3]
해달을 다룬 최초의 과학적 서술은 게오르크 빌헬름 스텔러가 1751년에 쓴 야장(野帳; feildnote)에서 발견할 수 있다. 이후 1758년에는 칼 폰 린네의 《자연의 체계》에서 해달을 다룬 것을 찾을 수 있다.[4] 이때 최초 학명은 Lutra marina였고, 수많은 변경을 거쳐 1922년에 Enhydra lutris로 학명이 확정되었다.[5] 속명 Enhydra의 어원은 고대 그리스어 en/εν과 hydra/ύδρα로, "물속"이라는 뜻이다.[6] 종명은 라틴어 lutris로, "수달"이라는 뜻이다.[7] 옛날에는 "바다비버"라고 불린 적도 있었으나[8] 사실 비버와는 근연관계가 멀다. 한편 서남안에 서식하는 바다수달(Lontra felina)이라는 진귀한 수달종이 따로 있는데, 해달과 구분할 필요가 있다. 수달류의 동물은 대부분 민물에 서식하지만 해달과 바다수달은 특이하게 해양 연안에 서식한다. 현재는 멸종한 바다밍크(Neovison macrodon)가 족제비과로서 역시 해양 환경에 적응한 종으로, 북아메리카 북동부에 서식했다.

 src=
캘리포니아 모로베이에서 떠다니고 있는 해달

진화

해달은 족제비과 동물 중 아주 무거운 축이다(신장은 큰수달이 더 길지만 훨씬 몸매가 날씬하다).[9] 족제비과에는 13종의 수달류 동물과 족제비류, 오소리류, 밍크류 등의 육상 동물들이 포함되어 있다. 족제비과 동물이면서 은신처나 소굴을 파지 않고, 제 기능을 하는 항문선이 없다는 점에서 해달은 특이하다.[10] 또한 해달은 물 밖으로 나가지 않고도 평생을 살 수 있다.[11] 해달속(Enhydra)의 유일한 종으로서, 해달은 다른 족제비과 동물과는 상당한 차이가 있어 1982년까지만 해도 과학자들이 해달이 바다표범과 가까운 근연이라고 생각했을 정도였다.[12] 유전적 분석 결과 해달 및 그 가장 가까운 현생 근연종인 얼룩목수달, 유럽수달, 민발톱수달, 작은발톱수달이 약 5백만 년 전의 공조상을 가지고 있음이 밝혀졌다.[13]

화석 증거에 따르면 해달속 계통은 북태평양에서 약 2백만 년 전에 분리되었으며, 현재는 멸종한 Enhydra macrodonta 종과 현대 해달인 Enhydra lutris 종이 발생하였다.[5] 해달은 홋카이도 북부와 러시아에서 최초로 진화하여 알류샨 열도, 알래스카 본토를 걸쳐 동쪽으로 퍼져나갔고, 그 뒤 남쪽으로 방향을 틀어 북아메리카 해안으로 퍼져나갔다.[14] 물속으로 들어간 것이 대략 5천만 년, 4천만 년, 2천만 년 전인 고래류, 해우류, 기각류와 비교하면 해달은 해양성 포유류계의 상대적 신참자라고 할 수 있다.[15] 하지만 새끼를 치기 위해서 지면이나 빙상 위로 올라가야 하는 기각류와 비교하면 해달이 해양 생활에 더욱 적응한 종이라 할 수 있다.[16]

아종

현재까지 3개의 아종이 발견되었다. 신체 크기 및 두개골과 치아 구조에서 차이점이 있는데, 다음과 같다.[9][17]

오리건주 서안에 해달을 재도입하려는 시도는 성공적이지 못했다. 하지만 1969년에서 1970년에 걸쳐 워싱턴주 서안에 해달을 재도입한 것은 매우 성공적이었으며 그 후 해달의 서식지가 넓어지고 있다. 이제는 후안데푸카 해협까지 그 서식지가 확장되었으며, 필라포인트에서도 해달을 볼 수 있을 정도로 서식지가 동쪽으로 확장되었다. 때때로 샌환 제도퓨젓사운드만 북안에서 발견되는 개체도 있다.

계통 분류

다음은 수달아과의 계통 분류이다.[2][21]

수달아과

큰수달

    아메리카수달속

북아메리카수달

       

바다수달

   

남아메리카수달

     

긴꼬리수달

         

해달

   

얼룩목수달

    수달속

수달

   

수마트라수달

   

일본수달

       

아프리카민발톱수달

     

작은발톱수달

   

비단수달

             

신체적 특징

 src=
N. N. 콘다코프가 그린 해달의 두개골.

해달은 해양 포유류로서는 아주 작은 종 중 하나이지만 족제비과 동물 중에서는 아주 무거운 축에 든다.[11] 수컷 해달의 체중은 22킬로그램~45킬로그램(49파운드~99파운드) 정도이며, 신장은 1.2미터~1.55미터(3피트 10인치~4피트 10인치) 정도인데, 체중 54킬로그램(120파운드)까지 나가는 표본이 기록된 바 있다.[22] 암컷은 그것보다 작아서, 체중은 14킬로그램~33킬로그램(31파운드~73파운드), 신장 1.0미터~1.4미터(3피트 3인치~4피트 7인치) 정도이다.[23] 해달의 수컷은 음경골이 매우 크고 묵직하며 위쪽으로 굽어 있다. 그 길이는 150밀리미터(5.9인치), 음경골 뿌리는 15밀리미터(0.59인치) 정도이다.[24]

 src=
해달은 모피가 두텁기 때문에, 땅 위로 올라오면 물속에 있을 때보다 몸집이 더 토실토실해 보인다.

대부분의 해양 포유류와 달리 해달은 고래지방을 가지고 있지 않으며, 대신 유달리 두꺼운 모피를 통해서 체온을 유지한다.[25] 해달의 털은 1평방센티미터 당 150,000가닥(1평방인치당 거의 백만 가닥) 이상 나 있으며, 해달의 모피는 그 어떤 동물보다도 털이 조밀하게 나 있다.[26] 해달 모피는 방수가 되는 길다란 보호털과 그 아래 짧은 잔털로 이루어져 있는데, 보호털이 물을 막아줌으로써 아래의 조밀한 잔털층이 마른 상태를 유지한다. 때문에 차가운 물이 피부에 직접 닿는 일이 없으며 열 손실을 제한할 수 있다.[23] 해달은 털갈이 철이 따로 없고, 매번 조금씩 탈모하고 계속 털이 나기 때문에 연중 내내 모피가 두터움을 유지한다.[27] 보호털의 방수 기능은 철저한 청결함에 달려 있기 때문에, 해달은 몸 어느 부위의 털이든지 닿아서 그루밍할 수 있는 능력을 가지고 있다. 피부가 늘어져 있으며, 골격이 희한할 정도로 유연한 덕분이다.[28] 모피의 색깔은 보통 진한 갈색에 은빛 회색의 얼룩이 나 있는데, 노란색이나 쥐색 계통의 갈색도 있고, 개중에는 거의 새까만 색도 있다.[29] 성체 해달은 머리, 목, 가슴의 털 색깔이 다른 부위보다 더 밝은 색을 띤다.[29]

 src=
리스본 수족관의 해달. 특유의 유연성을 이용해 그루밍을 하고 있다.

해달은 해양 환경에 여러 모로 적응한 모습을 보인다. 조그만 귀와 콧구멍은 열었다 닫았다 할 수 있다.[30] 뒷발은 길고 넓적하며 반반하기 때문에 헤엄칠 때 상당한 추진력을 낼 수 있게 해 준다.[31] 뒷발은 그 다섯째 발가락이 가장 길다. 이 발가락 덕분에 누워서 헤엄칠 수 있지만 걷는 것은 어려워한다.[32] 꼬리는 짧고 두꺼우며 약간 넓적한데 근육질이다. 짧은 앞발에는 오므릴 수 있는 갈고리발톱들이 나 있으며, 발바닥에 거칠거칠한 육구가 붙었기 때문에, 미끄러운 먹이를 잡기 용이하다.[33]

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이렇게 사지를 오므리고 잔다. 밴쿠버 수족관.

수중에서 해달은 꼬리와 뒷발을 비롯한 몸의 뒤쪽 부분을 위아래로 흔들어서 앞으로 나아간다.[31] 그리고 그 속도는 최대 시속 9킬로미터(시속 5.6마일)에 이른다.[9] 물속으로 들어가면 해달은 짧은 앞다리를 가슴에 딱 붙여 포개어 몸을 길고 유선형으로 만든다.[34] 한편, 수면 위로 올라오면 해달은 배를 드러내고 누워서, 발을 노 젓듯 움직이고 꼬리를 옆으로 흔들면서 떠다닌다.[35]

휴식을 취할 때는 사지를 모두 오므려 몸통에 접어 붙이고 체온을 보존한다. 반대로 날씨가 너무 더울 때는 뒷발을 물속에 넣어서 몸을 식히기도 한다.[36] 해달의 몸은 부력이 매우 커서 물에 잘 뜨는데, 이것은 해달의 폐활량이 매우 큰 것과(비슷한 덩치의 육상 포유류의 2.5배 정도이다)[37] 모피 속에 공기가 찬 것 때문에 그러한 것이다. 해달은 땅으로 올라오면 걸음걸이가 굴러다닐 듯 어설프지만 껑충껑충 뛰어서 도망갈 수는 있다.[32]

물이 어둡거나 탁할 때 해달은 길고 매우 민감한 수염과 앞발의 촉각으로 먹이를 찾는다.[11] 연구자들은 해달에게 잘 보이는 위치에서 연구진이 해달에게 접근했을 때, 해달 쪽으로 바람이 불면 해달이 보다 빠르게 반응하는 것에 주목했다. 이것은 해달의 후각시각보다 경고 감각으로서 더 중요하게 작용한다는 것을 시사한다.[38] 또 다른 관찰에서 밝혀진 바로는 해달의 시력은 물 위에서나 물속에서나 도움이 되는 수준이기는 하지만 물개류만큼 눈이 좋은 것 같지는 않다.[39] 청력은 특별히 좋은 편도 나쁜 편도 아니다.[40]

성체의 이빨은 32개이고, 그중 어금니는 둥글납작하여 음식을 잘라내기보다는 부수는 데 적합하다.[41] 아랫앞니가 세 쌍이 아니라 두 쌍인 육식성 동물은 기각류와 해달뿐이다.[42] 성체 해달의 치열3.1.3.12.1.3.2이다.[43]

해달의 기초 대사율은 비슷한 크기의 육상 포유류보다 2~3배 높다. 해달은 차가운 물속 환경에서 열 손실에 대응하기 위해 엄청난 열량을 태워야 하고, 매일 자기 체중의 25~38% 무게의 먹이를 먹어야 한다.[44][45] 소화 효율은 80~85% 정도이며,[46] 먹은 먹이는 3시간 정도면 소화가 끝나고 배설된다.[25] 수분은 대부분 먹이를 먹으면서 함께 섭취하는데, 다른 해양 포유류와 달리 바닷물을 마시기도 한다. 신장이 비교적 크기 때문에 바닷물에서 맹물을 얻어내고 진한 오줌을 배설한다.[47]

습성

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예민한 동모와 앞발로 해달은 그 촉각을 이용해 먹이를 찾는다.

해달은 주행성 동물이다. 해가 뜨기 한 시간쯤 전 아침부터 먹이를 잡아먹기 시작하고, 한낮 동안에는 쉬거나 잠을 잔다.[48] 오후가 되면 몇 시간 동안 또 먹이를 잡아먹다가 해가 지기 전에 그만두고, 한밤중 즈음에 다시 먹이를 잡아먹기도 한다.[48] 새끼를 데리고 있는 암컷은 특히 밤에 먹이를 먹는 경향이 있다.[48] 해달을 관찰한 결과 먹이를 찾고 잡아먹는 데 투자하는 시간은 하루에 24~60% 정도였으며, 이것은 서식지에 먹이가 얼마나 풍부한지에 따라 정해지는 것 같다.[49]

해달은 많은 시간을 투자해서 그루밍을 한다. 그렇게 함으로써 털을 깨끗이 하고, 엉킨 털을 풀고, 빠진 털을 제거하고, 털에서 물을 짜내고 털 속으로 공기를 통하게 한다. 관찰하는 도중 해달이 몸을 긁는 것이 보이기도 하는데, 털 속에 라든가 다른 기생충이 있는지 여부는 밝혀지지 않았다.[50] 먹이를 먹을 때 해달은 물속에서 몸을 틈틈이 굴리는데, 털에 묻은 음식 찌꺼기를 씻어내기 위한 것으로 보인다.[51]

먹이 사냥

해달은 짧은 시간 잠수하여 먹이를 사냥하는데, 종종 해저까지 내려간다. 약 5분 이상 숨을 참을 수 있지만[30] 보통 1분 정도 잠수하고, 아무리 길어도 4분 이상 잠수하지는 않는다.[23] 해달은 돌을 들었다 뒤집을 수 있는 유일한 해양 동물로, 먹이를 찾기 위해 앞발로 돌을 들고 뒤집는다.[51] 또한 해달은 수초에 붙어 있는 달팽이류 등 생물을 떼어내거나 조개를 찾기 위해 바닷속 진흙을 뒤질 수도 있다.[51] 또한 이빨보다 앞발을 사용하여 물고기를 사냥하는 유일한 해양성 포유류이기도 하다.[25]

양 앞다리 밑에는 각각 헐거운 살주머니가 있는데, 이 주머니는 가슴을 가로질러 이어져 있다. 해달은 이 주머니 안에 (먼저 왼쪽부터) 먹이를 모아서 수면으로 올라온다. 특이하게 주머니 안에 돌도 넣어 오는데, 이것은 조개류의 껍데기를 까부숴 열기 위한 것이다.[52] 그리고 해달은 물 위에 누운 채 떠서, 앞발로 먹이를 찢은 뒤 입으로 가져가서 먹는다. 작은 홍합 따위는 껍데기째 씹어 삼키기도 하지만 보다 큰 것은 속살을 비틀어 빼내 먹는다.[53] 이때 아랫앞니를 사용해 조개의 속살을 꺼내려고 한다.[54] 가시로 덮여 있는 성게를 먹을 때는 가시가 가장 짧은 성게 아랫면을 물어뜯는다. 그리고 성게의 부드러운 속살을 껍데기 속에서 핥아 빼먹는다.[53]

해달은 먹이를 사냥하고 먹을 때 돌을 사용하는, 즉 도구를 사용하는 몇 안 되는 포유류 동물이다.[55] 단단한 조개를 열기 위해 조개를 가슴 위에 올려놓고 양발로 돌을 들어 조개를 요란하게 두드린다. 해달이 전복을 돌덩어리에서 떼어내려고 돌멩이로 망치질하듯 전복을 찍어대기도 한다. 관찰 결과 그 타격 속도는 15초 동안 45번 정도이다.[23]

사회 구조

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물에 떠내려가지 않기 위해 해달은 서로 손을 잡고 잔다.[56] 몸의 부력이 매우 크다.

성체든 유체든 먹이 사냥은 혼자 하지만 해달은 휴식을 취할 때는 래프트(raft)라는 동성(同性) 무리와 함께 하는 경향이 있다. 래프트는 대략 10~100마리의 해달로 이루어져 있으며, 수컷 래프트가 암컷 래프트보다 규모가 크다.[57] 현재까지 발견된 래프트 중 가장 큰 것은 2000마리 이상의 해달들이 모여 있었다. 휴식하거나 먹이를 먹을 때 먼 바다로 떠내려가지 않기 위해 해달은 다시마류 해초에 자기 몸을 묶는다.[58]

번식 세력권을 유지하고 있으며 암컷들에게 선호받는 수컷이 짝짓기를 하게 된다.[59] 대부분의 서식지에서 가을이 짝짓기의 절정기이며, 수컷은 자기 세력권을 봄부터 가을까지만 지키고 있는다.[59] 이 기간 동안 수컷은 다른 수컷을 쫓아내기 위해 세력권의 경계를 순찰하는데,[59] 실제로 싸움으로 번지는 일은 드물다.[57] 성체 암컷은 수컷들의 세력권 사이를 자유로이 오갈 수 있는데, 대략 5 대 1의 비율로 암컷의 개체수가 수컷보다 더 많다.[59] 자기 세력권을 가지지 못한 수컷들은 자기들끼리 모여서 수컷만 있는 큰 무리를 이루고,[59] 암컷들의 구역을 헤집고 다니면서 짝짓기 상대를 찾는다.[60]

해달은 다양한 음성 행동을 보인다. 새끼의 울음소리는 갈매기의 것과 비교되기도 한다.[61] 암컷은 만족했을 때 구구구 거리는 소리를 내고, 이에 비해 수컷은 꿀꿀거리는 소리를 낸다.[62] 고통을 받거나 겁을 먹은 성체는 휘파람 소리, 쉬익 하는 새는 소리를 내고, 극단일 때에는 비명을 지르기도 한다.[61][63]

해달이 장난기 많고 사교적인 동물이긴 하지만 진정한 의미에서의 사회적 동물로는 취급받지 못한다.[64] 해달은 대부분의 시간을 혼자 보내고, 각각의 성체 해달은 사냥, 그루밍, 방어 등의 면에서 필요한 것을 스스로 충족할 수 있다.[64]

번식과 생활사

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짝짓기를 하는 도중, 수컷이 암컷의 코를 물어뜯는다. 그 탓에 피가 나고 흉터가 진다.

해달은 일부다처이다. 수컷 한 마리가 여러 암컷 동반자를 가진다. 하지만 발정기의 암컷과 그 짝이 며칠에 걸쳐 잠시 암수 한 쌍의 짝을 이루기도 한다.[51] 짝짓기는 물속에서 이루어지며 다소 거칠다. 수컷은 암컷의 코와 주둥이를 물어뜯어 흉터를 남기고, 어떤 때는 암컷의 머리를 물속에 처박기도 한다.[9] 최소 한 마리의 암컷이 코의 감염으로 인해 사망했음이 보고되어 있다.[65]

출산은 연중 일어나는데, 북방 개체군은 5월과 6월 사이, 남방 개체군은 1월과 3월 사이에 절정을 이룬다.[66] 해달은 착상 지연이 가능한 동물이기 때문에 임신 기간은 4개월에서 12개월까지 다양하게 나타난다. 착상 이후에는 4개월 동안 새끼를 배고 있는다.[66] 캘리포니아의 해달은 매년 새끼를 치는데, 그 빈도가 알래스카의 해달의 두 배 정도 높다.[67]

출산은 보통 물속에서 이루어지며, 한 배에 한 새끼를 낳고 막 태어난 새끼의 몸무게는 1.4~2.3킬로그램(3~5파운드)이다.[68] 2% 확률로 쌍둥이를 낳기도 한다. 하지만 그럴 경우 대개 쌍둥이 중 한 마리만 살아남는다.[9] 새끼는 태어나자마자 눈을 뜰 수 있고, 이빨 열 개가 보이고, 두꺼운 모피를 두르고 있다.[69] 어미는 태어난 새끼를 몇 시간 동안 핥고 부풀린다. 그루밍이 끝나면 새끼의 털 속에 공기가 들어가서 물 위에 코르크처럼 떠 있을 수 있다. 하지만 잠수는 하지 못한다.[70] 새끼의 솜털은 13주가 지나면 없어지고 성체의 털과 같은 새 털이 난다.[4]

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새끼를 가슴에 안고 떠다니는 어미 해달. 게오르크 스텔러는 “해달은 가히 믿을 수 없을 정도의 애착을 가지고 새끼를 포옹한다.”고 말했다.[71]

수유 기간은 캘리포니아 개체군은 6~8개월, 알래스카 개체군은 4~12개월 정도 계속된다. 동시에 1~2개월 정도 지나면 먹이 조각을 조금씩 주기 시작한다.[72] 복부의 유두에서 분비되는 해달의 젖은 지방이 풍부하여 족제비과 동물의 젖보다는 다른 해양성 포유류의 그것과 유사하다.[73] 새끼는 어미의 지도 아래 헤엄과 잠수를 연습하여 수 주가 지나면 바다 밑바닥까지 닿을 수 있다. 새끼가 처음 잡아오는 것은 알록달록한 불가사리나 조약돌 따위의 먹거리로서 가치가 없는 것들이다.[52] 그러다 6~8개월이 지나면 새끼는 독립하게 되는데, 먹이가 부족할 경우에는 어미가 새끼를 버릴 수밖에 없게 되는 경우도 생긴다.[74] 반대쪽 극적 사례로, 새끼가 거의 성체만 하게 자랐는데도 여전히 어미에게 보살핌을 받는 일도 있다.[68] 새끼 해달의 사망률은 높은 편으로, 특히 태어나서 첫 번째 겨울을 넘기지 못하고 죽어나간다. 한 추산에서는 태어나서 1년을 넘기는 새끼는 전체의 25%에 불과했고,[74] 경험이 많은 어미가 낳은 새끼들의 생존률이 높았다.[75]

새끼를 먹이고 키우는 모든 일은 암컷이 도맡아 한다. 또한 가끔 고아가 된 새끼를 거두어 키우는 것도 목격된다.[76] 2010년에 캘리포니아 앞바다에서 홀로 떨어진 생후 5주의 새끼 암컷 해달을 몬트레이베이 수족관으로 데려왔더니 나이 9살의 암컷 해달이 먹는 법, 헤엄치는 법, 그루밍하는 법을 가르쳐 주는 것이 관찰되었다.[77][78] 이 새끼 해달(이름 "키트")은 2년 뒤인 2012년 6월에 샌디에이고로 옮겨갔다가 2013년 1월에 몬트레이베이로 돌아왔다.[79] 한편 양어미(이름 "마에")는 키트가 샌디에이고에 가 있던 사이 2012년 11월 17일에 11살로 죽었다.[80][81]

어미 해달의 새끼를 향한 헌신의 수준으로 여러 사람들이 여러 기록을 남긴 바 있다. 어미는 새끼에게 거의 끊임없는 관심을 쏟고, 찬물에 닿지 않도록 가슴에 올려둔 뒤 조심스럽게 털을 그루밍해 준다.[82] 먹이를 잡을 때는 새끼를 물 위에 남겨두고 잠수하는데, 떠내려가지 않도록 켈프류 수초로 묶어 놓는다.[83] 새끼는 잠들어 있지 않다면 어미가 돌아올 때까지 시끄럽게 울어댄다.[84] 새끼가 죽으면 어미는 며칠 동안 새끼의 시체를 계속 데리고 다닌다.[71]

암컷 해달은 태어나고 3, 4년, 수컷은 5년이 지나면 성적으로 성숙한다. 하지만 수컷은 성적으로 성숙했다 해도 그 뒤로 몇 년 동안은 제대로 새끼를 치지 못한다.[85] 한편 포획된 수컷이 19살의 나이에 새끼를 친 바 있다.[68] 야생에서 해달의 최대 수명은 23살 정도이고,[23] 평균 수명은 수컷이 10~15살, 암컷이 15~20살 정도이다.[86] 인간에게 잡혀 사는 해달은 20살을 넘겨 사는 일이 많은데, 시애틀 수족관의 암컷은 28살까지 살다 죽었다.[87] 야생 해달은 그 이빨이 닳는 일이 많고, 이것으로 사육 상태보다 수명이 짧아지는 것으로 보인다.[88]

개체 분포

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캘리포니아 주 모로베이에서 떠다니고 있는 해달.

해달은 수심 15~23미터(50~75피트) 정도의 연안 지역,[89] 즉 해안가에서 1킬로미터(⅔마일) 이내에 서식한다.[90] 해달은 보통 거친 바닷바람을 막을 수 있는 바위투성이 해안지대, 켈프림, 보초 등지에서 찾을 수 있다.[91] 해달은 대부분 암석 기층(基層; substrate) 지역에서 생활하지만 해저가 진흙이나 모래로 이루어진 지역에서도 살 수 있다.[92] 해달은 유빙 사이에서는 생존할 수 있어도 정착빙에서는 살아남을 수 없는 고로, 그 서식지는 얼음으로 인한 북방 한계를 가진다.[93] 해달 개체는 대략 1 킬로미터 길이의 행동 범위를 차지하며, 연중 계속 그 행동권에 머무른다.[94]

해달의 개체수는 한때 150,000마리에서 300,000마리에 달한 것으로 생각되며,[8] 그 서식지는 일본 북부에서 시작하여 멕시코 바하칼리포르니아반도 중부까지 이르는, 북태평양을 가로지르는 거대한 활꼴을 그렸다. 그러나 1740년대부터 시작된 모피 거래로 인해 해달의 개체수는 13개 무리 1,000~2,000마리 정도까지 격감하였다. 해달의 개체수 복원 현황은 옛 서식 범위의 약 3분의 2에 해당하는 지역마다 제각각이다. 높은 개체 밀도를 자랑하는 지역이 있는가 하면 아직도 멸종을 위협받고 있는 지역도 있다. 현재 러시아 동안, 알래스카, 브리티시컬럼비아, 워싱턴주, 캘리포니아에서는 해달의 개체수가 안정 국면에 접어들었으며, 일본멕시코에서도 재정착이 보고되고 있다.[95] 2004년에서 2007년 사이에 이루어진 추산 결과 세계적으로 약 107,000마리의 해달이 있는 것으로 추산되었다.[4][96][97][98][99]

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1870년에서 1924년 사이 코만도르 제도의 해달 사냥 그래프

러시아

현재 해달 서식지로서 가장 안정되고 안전한 곳은 러시아이다.[100] 19세기 이전에는 쿠릴 열도 일대에 20,000마리에서 25,000마리의 해달이 서식했으며, 캄차카코만도르 제도 근처에는 더 많이 살았다. 대남획시대 이후 이 일대, 현 러시아의 해달 개체수는 고작 750마리에 불과한 바 있었다.[96] 2004년 현재 해달들은 이 지역 모든 옛 서식지에 재도입되었으며, 그 개체수는 도합 27,000마리 정도로 추산된다. 이 중 약 19,000마리는 쿠릴 열도에, 2000~3500마리가 캄차카에, 나머지 5000~5500마리는 코만도르 제도에 서식한다.[96] 개체수 성장률이 약간 둔화되었으며, 그 수가 환경용량에 도달했다고 생각되고 있다.[96]

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눈 감고 떠다니는 해달.

알래스카

알래스카는 해달 서식지의 중앙 지역이다. 1973년에 추산한 알래스카의 해달 개체수는 약 100,000마리에서 125,000마리 정도였다.[101] 하지만 2006년까지 알래스카의 해달 수는 73,000여 마리로 떨어졌다.[97] 알류샨 열도의 해달 개체수가 급락한 것이 이 개체수 감소의 대부분 비율을 차지하고 있다. 이 개체수 급락의 원인은 명확하지 않으나 범고래의 포식 활동으로 인한 것일 가능성이 제기되어 있다.[102]

프린스윌리엄 해협의 해달 개체군 역시 1989년 엑손 발데스 기름 누출 사건으로 수천여 마리의 해달이 떼죽음을 당함으로써 직격타를 맞았다.[51]

브리티시컬럼비아와 워싱턴

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존 웨버의 《해달》. 1788년경.

알래스카 남부에서 북아메리카 해안선을 따라 분포하는 해달 서식지는 불연속된다. 밴쿠버섬에서는 잔류 개체군이 20세기까지 존속했으나 1911년 국제보호조약에도 불구하고 결국 1929년에 키유쿠트에서 최후의 해달이 잡힌 이후 자취를 감추었다. 1969년에서 1972년 사이, 89마리의 해달이 알래스카에서 밴쿠버섬 서안으로 공수 또는 수송되었다. 이 89마리는 2004년에는 3,000마리 이상으로 불어났으며, 서식지도 뱅쿠버 서안에서 북으로는 스콧곶, 남으로는 바클리 해협까지 확장되었다.[103] 1989년에는 브리티시컬럼비아 중부 해안에서 외딴 곳에 떨어져 있던 군집이 발견되었다. 2004년 현재 300마리에 이르는 이 군집이 알래스카에서 공수된 해달인지 또는 모피잡이에서 살아남은 해달이 존속한 것인지는 밝혀지지 않았다.[98]

1969년과 1970년에는 해달 59마리를 암치트카섬에서 워싱턴주로 들여왔다. 2000년부터 2004년까지 이루어진 연례 조사에서 개체수는 504~743마리로 불어났으며 서식지는 올림픽반도에서 디스트럭션섬과 필라포인트까지 넓어졌음이 보고되었다.[4]

브리티시컬럼비아와 워싱턴의 해달은 거의 모두 외부 연안에서만 찾아볼 수 있다. 올림픽 해안을 따라 해변에서 6피트 떨어진 곳까지 가까이 접근하기도 하지만 샌환 제도푸젓사운드만에서 보고된 해달 목격담은 대부분 북아메리카수달을 잘못 본 것으로 판명되었다. 북아메리카수달이 해변가에 흔히 나타나기 때문에 헷갈린 것이다. 다만 1990년대 중반의 목격담 몇몇은 생물학자들에게서 사실로 확인되었다.[4]

캘리포니아

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새끼에게 젖을 먹이는 해달. 캘리포니아에는 3,000마리 이상의 해달이 살고 있으며, 이들은 1938년에 발견된 해달 약 50마리의 후손이다.

2012년 봄, 미국 지질조사국(USGS)에서 실시한 캘리포니아의 해달 머릿수 조사 결과 총 2,792마리가 추산되었다. 이것은 2007년 봄에 정점을 찍은 3,026마리보다는 감소했지만 2010년의 2,711마리보다는 증가한 것이다.[99][104][105] 모피 거래가 시작되기 전의 개체 수는 약 16,000마리 정도였다. 현재의 캘리포니아의 해달들은 1938년에 빅서의 빅스비 다리 옆에서 발견된 약 50마리가량의 해달 군집의 후손이다.[106] 주요 서식지는 점차 확장되어 산마테오 군피죤포인트에서 산타바바라 군에 이른다.[105] 1980년대 후반, 미국 어류 및 야생동물관리국(USFWS)은 캘리포니아 해달 약 140마리를 남부 캘리포니아 산니콜라스섬으로 옮겼다. 그런데 생물학자들의 생각과는 의외로, 산니콜라스에 방사된 해달들은 거의 모두 캘리포니아 본토로 헤엄쳐 돌아가 버렸다.[107] 섬 주위의 풍부한 먹이 덕분에 조금씩 개체수가 늘어나는 추세긴 하지만[107] 2005년 현재 산니콜라스에 남아 있는 해달은 30마리뿐이다.[108] 해달 이주 프로그램을 검정한 계획서에서는 향후 5~10년 안에 해달 개체수가 환경용량에 도달할 것이라고 예측했었다. 그러나 2012년 현재 산니콜라스섬의 해달 개체수는 약 50마리 정도로 증가했을 뿐이다.[109]

FWS가 해달 이주 계획을 시행했을 당시, 당국에서는 캘리포니아 개체군의 "영역 관리"(zonal management) 역시 시행하려 시도한 바 있다. 해달과 인간 어업 활동의 충돌을 조정하기 위해 포인트컨셉션에서 멕시코와의 국경에 이르는 "해달 없는 영역"(otter-free zone)을 공표한 것이다. 이 영역 안에서는 산니콜라스섬만 해달 서식지로 지정되었고, 그 외 다른 곳에서 발견된 해달은 포획하여 이동시킨다는 계획이었다. 그러나 이동된 해달 중 많은 수가 폐사했고, 규제를 무시하고 월경하는 수백 마리의 해달을 모두 포획할 실질적 수단이 없었기 때문에 이 계획은 폐기되었다.[110] 산타바바라 지역의 환경보호센터와 Otter Project가 제기한 소송에 대응하여 2012년 12월 19일 USFWS는 "해달 없는 영역" 실험은 실패로 끝났음을 인정하고, 해달을 다시 멸종위기종으로 취급, 포인트컨셉션 남안에 군집을 재조성하여 보호하겠다고 선언했다.[111]

한때 샌프란시스코만에 해달이 넘쳐났던 적도 있었다.[112] 역사 기록을 살펴보면 러시아-아메리카 회사가 여러 차례에 걸쳐 알류트족들을 몰래 샌프란시스코 만으로 데리고 가서, 현재의 산호세, 산마에토, 산브루노, 앤젤섬 일대의 하구 퇴적지에서 해달을 사냥하게 시켰음을 알 수 있다. 이때 알류트족들은 에스파냐인들에게 붙잡혀 가거나 사살당하기도 했다.[113] 로스 요새를 세운 이반 쿠스코프는 1812년에 보데가만 2차 항해를 했을 때 해달이 드물어져서, 샌프란시스코 만으로 알류트족들을 보냈다. 거기서 그들은 다른 러시아 패거리와 미국인 패거리를 만났고, 3개월에 걸쳐 1,160마리의 해달을 잡았다.[114] 이 지역의 해달 서식지는 1817년이 되자 사실상 씨가 말랐으며, 러시아인들은 샌프란시스코 너머 먼 남쪽에서도 해달 사냥을 하려고 에스파냐와 멕시코 측의 허락을 받고자 하였다.[115] 샌프란시스코의 해달 개체군은 1840년까지는 명맥은 유지한 것 같다. 1840년 당시 보스턴 출신의 존 바티스타 로저스 쿠퍼 선장이라는 자가 푼타데쿠엔틴 토지불하지(현재의 캘리포니아주 마린 군)를 임대하기 위해 멕시코 주지사 후안 바티스타 알바라도에게 허가를 받았고, 이와 함께 해달 수렵 허가증도 함께 받았다. 전하는 바에 따르면 그 당시 코르테마데라 개울 어귀에 해달이 흔했다고 한다.[116]

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갈매기와 해달. 2007년 캘리포니아.

빅서에서 발견된 약 50마리를 1911년 보호한 이래 남방해달의 서식지는 계속 확장되는 추세이나 2007년과 2010년 사이 해달 개체수와 서식지는 다소 줄어들었다.[117] 2010년 봄 현재, 남방해달의 서식지 북방 한계선은 투니타스 개울에서 남동쪽으로 2킬로미터 정도 떨어진 피죤포인트로 옮겨갔고, 남방 한계선은 COP 유전에서 가비오타 주립공원으로 이동했다.[118] 최근에는 특정 시아노박테리아(마이크로시스티스Microcystis)가 생산하는 마이크로시스틴이라는 독소가 해달이 먹이로 삼는 조개에 집중 감염되어 해달을 중독시키고 있다. 시아노박테리아는 질소와 인이 풍부한 고인 물에서 번성한다. 이 질소와 인은 대개 오수 정화조나 농업용 비료가 유출된 것으로, 우기에 유속이 빠를 때 바다로 유입될 수 있다.[119][120] 2010년, 캘리포니아 해안선을 따라 많은 수의 해달 시체가 발견되었으며, 상어 습격률이 증가한 것 역시 해달의 죽음을 재촉하는 요소로 작용하고 있다.[121] 백상아리(Carcharodon carcharias)는 상대적으로 지방이 빈약한 편인 해달을 잡아먹지는 않지만 상어에 물려서 죽은 해달 시체는 1980년에 8%, 1990년에 15%, 2010년과 2011년 사이에 30%로 증가 추세에 있다.[122]

2011년에는 캘리포니아 남부에서 해달이 두 번 관측되었는데, 한 번은 라구나 해변에서, 다른 한 번은 샌디에이고 근교 Zuniga Point Jetty에서였다. 이렇게 남쪽에서 해달이 관찰된 것은 기록상 30년 만에 처음 있는 일이다.[123]

오리건

최후의 오리건 토종 해달은 1906년에 사살된 것으로 생각된다. 1970년과 1971년, 알래스카 암치트카섬에서 95마리의 해달을 오리건 남부 해안으로 공수했다. 하지만 이 재도입 계획은 실패했고 얼마 있지 않아 해달은 다시 오리건에서 사라졌다.[124]

2004년에는 수컷 해달 한 마리가 케이프아르고의 심프슨 암초를 차지하고 6개월 동안 거기서 살았다. 이 수컷은 워싱턴의 군집에서 떨어져 나온 것으로 추정되었는데, 연안 폭풍이 한 차례 휩쓸고 지나간 뒤 사라져 버렸다.[125]

보다 최근에는 2009년 2월 18일에 오리건주 디포베이에서 수컷 한 마리가 목격되었다. 이 수컷은 캘리포니아나 워싱턴에서 흘러 들어온 것으로 추정되고 있다.[126]

생태

식성

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해달은 켈프를 뜯어먹고 사는 동물들을 잡아먹음으로써 켈프림을 건강하게 유지시킨다.

해달이 먹이로 삼는 종은 100종이 넘는다.[127] 그중에서 해달은 각종 해양 무척추동물을 주로 잡아먹는데, 해달의 먹이가 되는 해양 무척추동물은 성게를 비롯해서 대합·홍합 등 다양한 쌍각류전복, 그외 연체동물, 갑각류, 달팽이류 등이 있다.[127] 크기로 보자면 작은 삿갓조개에서부터 문어처럼 큰 것까지 각양각색이다.[127] 성게, 대합, 전복 따위의 먹이의 크기가 다양할 때, 해달은 비슷한 종류의 작은 먹이보다 큰 먹이를 선택하는 경향이 있다.[127] 캘리포니아에서는 해달이 3인치(7센티미터)보다 작은 피스모대합은 무시하는 것이 관찰되기도 했다.[128]

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배 위에 조개를 올려놓은 해달. 코의 흉터를 보아 암컷이다.

보다 북쪽의 서식지 일부에서는 해달이 물고기를 잡아먹기도 한다. 1960년대에 암치트카섬에서 수행된 실험에서(이때 해달의 개체수는 환경용량), 해달의 위장 속의 음식물을 확인했더니 50%가 물고기였다.[129] 물고기 종은 대개 바다 밑바닥에 살거나, 몸을 많이 움직이지 않거나, 느릿느릿 움직이는 붉은횟대(Hemilepidotus hemilepidotus)나 참복과 등이었다.[129] 하지만 북아메리카 대륙 연안 알래스카 남부에서는 해달의 먹이로서의 물고기는 거의 무시할 수 있을 정도로 사소하다.[4][130] 또한 흔히 묘사되는 것과 달리 해달은 불가사리는 거의 먹지 않으며, 켈프류 식물은 해달의 몸속에서 전혀 소화되지 않고 배설된다.[131]

해달 개체들은 사는 곳에 따라 먹이의 종류와 먹이를 잡는 방법이 조금씩 다르며, 자기 어미의 먹이 잡는 패턴을 따라하는 경향이 있다.[132] 해달은 자기들이 선호하는 먹이, 예컨대 성게 같은 것의 개체수를 급격히 감소시킬 수 있으며, 인간의 어로 활동 등 다양한 요소가 작용하기 때문에 각 지역의 해달 개체군은 시간이 흐름에 따라 먹이를 바꾼다.[4] 어느 지역에서는 바위틈 깊숙한 곳에 있는 것을 제외한 전복들을 싹쓸이할 수도 있었지만[133] 해달이 특정 지역에서 특정 먹이 종을 완전히 절멸시키는 일은 없다.[134] 2007년에 캘리포니아에서 이루어진 연구에서는 먹이가 상대적으로 부족한 지역에서는 그에 비해 다양한 종류의 먹이가 소비됨이 밝혀졌다. 하지만 놀랍게도 해달 개체 각각의 식성은 먹이가 풍부한 지역보다 먹이가 부족한 지역에서 특정 먹이에 특수화하여 있었다.[107]

핵심종

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캘리포니아 연안 후미진 지역. 이런 곳에 모피 거래에서 살아남은 소수의 해달 군집이 숨어 있다.

해달은 핵심종 개념의 고전적 예시이다. 해달의 개체수와 몸집이 작음에 비해 그 존재는 생태계에 큰 영향을 미친다. 해달은 성게 등 특정 저생성 초식동물의 개체수를 억제한다. 성게는 켈프의 줄기 아랫부분을 갉아먹어 켈프가 떠내려 가 죽게 만든다. 켈프림으로 인해 제공되는 생물 서식지와 영양소가 손실되면 해양 생태계에 엄청난 누적 효과를 일으키게 될 것이다. 북태평양에는 해달이 서식하지 않으며, 때문에 성게가 풍부하여 켈프림이 없고 성게 불모지가 형성되어 있다.[9]

캐나다 브리티시컬럼비아 주 해안에 해달을 재도입한 결과 연안 생태계의 건강에 획기적 진보가 있었다.[135] 또한 해달 개체수가 다시 늘어난 알류샨과 코만도르, 캘리포니아 빅서 해안 등지에서도 유사한 변화가 관찰되고 있다.[136] 다만 캘리포니아의 일부 켈프림 생태계는 해달 없이도 번창하고 있는데, 다른 요소로 성게가 조절되는 것 같다.[136] 켈프림을 유지하는 데에 해달의 역할은 이나 하구퇴적지 등 닫혀 있는 지형보다 먼 바다를 향해 열려 있는 연안 지형에서 더 중요한 것으로 관찰되었다.[136]

켈프림의 성장을 촉진시키는 것 외에도 해달은 홍합류에게 점령당하기 쉬운 바위투성이 지역에도 큰 영향을 미친다. 해달이 바위에서 홍합류를 제거하여 홍합과 경쟁하는 종이 살아갈 수 있는 공간을 확보하고, 그로 인하여 해당 지역의 생물 다양성을 증가하는 데 기여한다.[136]

천적

해달이 다른 동물에게 잡아먹히기도 하지만 그렇게 흔히 일어나는 일은 아니다. 많은 포식자들은 수달류의 자극적인 취선을 불쾌해 한다. 어린 포식자가 수달류 동물을 죽이기만 하고 먹지 않는 경우도 있다. 해달을 잡아먹는 포식자 중 포유류로는 범고래바다사자가 있고, 흰머리수리 역시 수면에 누워 있는 해달을 채어가는 때가 있다.[55]

땅에서는 어린 해달이 이나 코요테에게 공격받기도 한다. 캘리포니아에서는 상어, 특히 백상아리에게 물려 죽는 것이 해달의 사인(死因) 중 10%를 차지하는 것으로 추산되었으며, 또한 해달의 서식지가 북쪽으로 더 확장되지 못하는 이유 중 하나로 상어가 있는 것으로 보인다.[137] 백상아리는 해달의 주요 포식자로 추측되고 있으며, 상어에게 물려 죽은 해달 시체도 발견된다. 하지만 상어가 실제로 해달을 잡아먹는다는 구체적 증거는 아직 없다.[137]

인간과의 관계

모피 거래

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1896년, 어널래스카섬알류트족 남성들. 해달 사냥을 위해 방수 카약과 옷가지를 사용했다.

해달의 털은 포유류 중 아주 두꺼운 편이다. 해달의 아름다운 털은 많은 사냥꾼들의 목표가 되었다. 고고학적 증거에 따르면 수천 년 전의 원주민들 역시 식량과 털을 얻을 목적으로 해달을 사냥한 바 있다.[8] 사냥꾼들과 상인들은 가장 귀중한 모피였던 해달 가죽의 외국 수요를 충족시키기 위해 전 세계를 헤집고 다녔고, 18세기에 시작된 해양 모피 거래의 일부였던 광범위한 해달 남획의 결과 대략 1백만 마리의 해달이 죽임을 당했다.[8]

18세기 러시아인들이 쿠릴 열도에서 해달을 사냥하기 시작했고,[8] 사냥한 해달은 캬흐타에서 중국인들에게 팔았다. 이 당시 러시아는 태평양 북단을 탐험하고 있었으며, 북빙양 해안선의 지도를 작성하고 시베리아에서 북아메리카로 가는 길을 찾기 위해 비투스 베링을 파견했다.[138] 1741년, 2차 북태평양 항해 당시 베링은 코만도르스키예 제도 베링섬에서 난파를 당했고, 그 자신을 포함하여 승무원 다수가 사망하였다.[138] 자연학자 게오르크 스텔러를 포함한 생존 승무원들은 섬의 해변에서 해달을 발견하고, 그해 겨울 해달을 사냥해 잡아먹고 그 가죽으로 도박을 하면서 보냈다.[138] 거의 1,000 마리의 해달을 잡아 죽인 그들은 시베리아로 돌아가 비싼 값을 받고 가죽을 팔았다.[138] 이렇게 하여 소위 말하는 "대남획"(Great Hunt) 시대가 시작되어 그 뒤로 백여년 동안 지속되었다. 러시아인들은 해달 모피가 러시아의 시베리아 팽창의 주요 동기 부여였던 흑담비 모피보다 더 값나간다는 것을 깨닫게 되었다. 베링 탐사대의 생존자들이 가지고 온 해달 가죽을 캬흐타에서의 값으로 팔았다면 그들은 베링의 탐사 비용의 10분의 1 정도를 지불할 수 있었을 것이다.[139] 1775년 오호츠크에서 흑담비 모피 값이 2.5 루블이었던 데 반해 해달 모피는 50 ~ 80 루블이나 나갔다.

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런던 모피 시장의 해달 모피 매출량(단위: 천). 해달 개체수의 감소로 인해 1880년대부터 매출 급락이 시작된다.[140]

러시아인들의 모피사냥 원정으로 인해 코만도르 제도의 해달 개체수는 대폭 감소했고, 1745년이 되자 러시아인들은 알류샨 열도로 옮겨갔다. 러시아인들은 처음에는 원주민인 알류트족과 거래하여 수달 가죽을 얻었지만 나중에는 알류트족을 노예로 만들고, 여자와 아이는 인질로 잡았으며 남자는 고문하고 죽여서 사냥을 하도록 강요했다. 많은 알류트족이 러시아인들에게 살해당하거나 러시아인들이 옮겨온 병으로 죽었다.[141] 러시아의 자체 조사에 따르면 알류트족 인구는 20,000 여명에서 2,000 여명으로 감소했다.[142] 1760년대에는 러시아인들이 알래스카에 도달했다. 1799년 러시아 황제 파벨 1세는 경쟁하는 모피 사냥 회사들을 러시아-아메리카 회사로 통폐합하고, 이 회사에 황실 인가와 보호를 보장하여 거래권과 영토 습득을 독점하게 했다. 상인들이 관리하던 회사 운영이 알렉산드르 1세 치하에서는 제국 해군의 소관으로 이전되었다. 이것은 원주민들에게의 학대 행위에 관한 보고서를 해군 장교들이 제출한 데 그 원인이 크다. 1818년 알래스카 선주민들은 러시아 제국의 읍민과 동등한 시민권을 보장받게 되었다.[143]

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해달 가죽. 1892년.

남쪽에서는 다른 나라들이 해달 사냥에 뛰어들었다. 현재의 멕시코캘리포니아가 되는 해안선을 따라 에스파냐 탐험가들이 아메리카 토착민들에게서 해달 가죽을 사서 아시아에 팔았다.[141] 1778년, 영국의 탐험가 제임스 쿡 선장이 밴쿠버섬에 도달하여 선주민들에게서 해달 모피를 구입했다.[144] 이후 쿡의 배가 중국 항구에 입항하자 이 해달 가죽들은 고가에 빠르게 팔려나가 "부드러운 황금"(soft gold)이라 알려지게 되었다. 그 말이 퍼지자 유럽과 북아메리카 전역에서 많은 사람들이 해달 모피 무역에 뛰어들기 위해 태평양 북서부로 모여들었다.[144]

러시아는 사냥터를 남쪽으로 확장했고, 러시아 관리자들에게 하청을 받은 미국 선적 선장들과 알류트족 사냥꾼들이 현재의 워싱턴, 오리건, 캘리포니아에서 사냥에 착수했다.[145] 1803년에서 1846년 사이, 72척의 미국 배가 캘리포니아 해달 사냥에 참가하였으며, 약 40,000 마리의 가죽과 꼬리를 획득했다. 같은 기간 동안 러시아-아메리카 회사 선적의 배는 13척뿐이었으며 수렵한 해달 가죽도 5,696 마리였다.[146] 1812년, 러시아인들은 현재 로스 요새라고 알려진 농경 정착지를 캘리포니아 남부에 건설하고 남방 사령부로 삼았다.[144]

결국 해달 개체수가 너무 감소했기 때문에, 상업적 수렵이 불가능한 지경에 이르렀다. 알류샨 열도에서의 해달 사냥은 러시아-아메리카 회사가 보존 측정을 한 1808년 이후 중단되었다.[147] 1834년에는 회사 측에서 추가적 규제를 요청했다.[147] 1867년에 러시아가 미국에 알래스카를 매각했을 당시 알래스카의 해달 개체군은 100,000 마리 이상으로 되살아나 있었다. 하지만 미국인들이 사냥을 재개하자 해달은 또다시 빠르게 씨가 말랐다.[148] 해달이 귀해짐에 따라 해달 모피 값도 상승했다. 1880년대에 런던 시장에서 해달 가죽의 가격은 105~165 달러였으나 1903년에는 1,125 달러까지 치솟았다.[68] 1911년, 러시아, 일본, 대영제국(캐나다), 미국은 해달 및 물개류 보호 국제조약을 체결하고, 해달 수렵 결과물의 지불 중지를 결의했다.[149] 이때 야생 해달은 1,000~2,000여 마리가 남아 있을 뿐으로, 많은 사람들은 이 종이 멸종될 것이라고 생각했다.[4]

복원과 보존

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엑손 발데즈 유조선의 항적을 따라 시커먼 윤기 흐르는 기름이 프린스윌리엄 해협을 뒤덮고 있다.

20세기에 걸쳐 옛 서식지의 3분의 2에 해당하는 지역에서 해달의 개체수가 증가하였으며, 이 개체수 복원은 해양 환경보존의 가장 성공한 사례로 생각되고 있다.[150] 그러나 IUCN은 여전히 해달을 멸종 위기종으로 분류하고 있으며, 해달에게 심각한 위협으로 작용하는 요소로 기름 유출, 범고래의 포식, 밀어(密漁; poaching), 인간의 어업 활동과의 충돌을 들었다. 해달이 낚시도구에 얽혀서 익사하는 경우도 있기 때문이다.[1] 이제 미국에서 해달 사냥은 원주민들의 제한적 수렵 행위를 제외하면 모두 불법이다.[151] 1991년에 소련이 붕괴한 이후 러시아 극동에서는 밀어 행위가 심각한 걱정거리였다. 하지만 법적 제재가 강화되고 경제사정이 호전되면서 밀어 행위는 눈에 띄게 줄어들었다.[100]

해달에게 가장 심각한 위협은 기름 유출로,[55] 체온 유지를 모피에 유지하는 해달에게 기름 유출은 특히 치명적이다. 해달의 털이 기름을 먹으면 그 안에 공기를 채울 수 없게 되어 저체온증으로 순식간에 죽음에 이른다.[55] 해달이 기름을 마시거나 그루밍하다 삼키게 될 때 신장, 에 손상을 입게 된다.[55] 1989년 3월 24일의 엑손 발데스 기름 누출 사건 당시 프린스윌리엄 해협에서 수천 마리의 해달들이 폐사했다. 2006년에도 해당 지역에 잔류한 기름은 계속해서 오염에 영향을 미쳤다.[152] 당시 대중매체의 보도로 해달에게 대중의 동정이 형성되었고, 미국 어류 및 야생동물관리국 대변인은 다음과 같이 논평했다.

장난기 많고 사진발 잘 받는, 죄 없는 구경꾼이던 해달은 완벽한 피해자의 역할을 떠안게 되었다. … 즐겁게 뛰어놀던 귀여운 해달들은 기름과의 싸움에서 패배하여, 갑작스럽게도 기름 범벅이 되어 고통 속에서 겁에 질려 죽어가고 있다.[4]

캘리포니아, 워싱턴, 브리티시컬럼비아의 해달 서식지가 지리상 좁다는 것은 한 번 대형사고가 터지면 해당 주의 해달 전체의 생존에 재앙이 일어날 것임을 의미한다.[4][45][51] 기름 유출을 방지하고 해달 구조를 준비하는 것은 해달 구조 활동에서 주된 초점이 맞춰진 중요한 일이다. 또한 해달 개체수를 늘리고 서식지를 넓히는 것 역시 한 번의 기름 유출로 해달들이 싹쓸이되는 것을 막을 수 있다.[4] 하지만 해달이 조개 수를 감소시킨다는 인식, 상업, 오락, 자급을 이유로 조개 채취를 옹호하는 이들은 해달의 서식지가 넓어지는 것에 반대한다. 때로는 어부나 다른 인간들이 불법으로 해달을 잡아 죽이는 일도 있다.[153]

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올림픽 해안 국립해양보호구역의 해달. 뒷발의 기묘한 모양에 주목할 것. 바깥쪽으로 갈수록 발가락이 길어진다.

최근 수십년 사이, 알류산 열도에서는 예상치 못한 해달의 급격한 감소가 일어나고 있다. 1980년대의 알류샨 열도는 약 55,000 마리에서 100,000 마리의 해달의 보금자리였으나 2000년에는 6,000 마리 정도로 개체수가 줄어들었다.[110] 가장 널리 인정받는 견해(아직 논쟁의 여지가 있다)는 범고래들이 해달을 잡아먹었다는 것이다. 해달이 사라지는 패턴이 포식의 증가와 일치한다. 하지만 범고래가 정말 해달을 잡아먹는지 또 얼마나 잡아먹는지 구체적 증거는 아직까지 없다.[102]

또 다른 요주의 지역은 캘리포니아로, 1990년대 해달 복원 정도가 등락을 거듭하거나 감소하고 있다.[154] 성체 및 성장기가 거의 끝난 개체의 사망률이 유달리 높으며, 특히 암컷의 사망률이 높음이 보고되었다.[99] 죽은 시체의 부검 결과 질병, 특히 톡소플라즈마 곤디이(Toxoplasma gondii)와 구두충 기생이 캘리포니아 해달의 주요 폐사 원인으로 밝혀졌다.[155] 해달에게 매우 치명적인 톡소플라즈마 기생충은 야생고양이 및 집고양이와 주머니쥐 등이 숙주이며, 집고양이의 분비물이 하수도를 통해 바다로 흘러들어가 해달에게 감염될 수 있다.[155][156] 캘리포니아해달의 폐사에 질병이 큰 것은 확실하지만 어째서 다른 지역에 비해 캘리포니아의 해달 개체군이 다른 지역의 해달 개체군보다 질병에 더 큰 영향을 받는지는 아직 밝혀지지 않았다.[155]

미국, 러시아, 캐나다 각국은 해양보호구역을 지정하여 해달 서식지를 보존하고 있다. 해양보호구역에서는 폐기물 투기나 원유 시추와 같은 오염 행위가 일반에서 금지된다.[157] 몬트레이 만 국립해양보호구역에는 약 1,200 마리, 올림픽 해안 국립해양보호구역에는 500 마리 이상의 해달이 살고 있다.[158][159]

경제적 영향

해달이 좋아하는 먹이, 특히 전복, 대합, 는 인간의 식량 자원이기도 하다. 몇몇 지역에서는 조개류 수확량의 급락이 해달의 탓이라고 생각하고 있으며, 해산물을 둘러싼 해달과 인간의 경쟁을 어떻게 조절할 것인지를 두고 격렬한 공개 토론회가 벌어졌다.[160]

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모스랜딩의 이 해달처럼, 해달은 캘리포니아 몬트레이만 일대의 관광자원이다.

남획, 질병, 오염, 지진 등으로 인한 조개 양 감소까지 해달에게 책임을 지우려 하는 경우도 있었기 때문에 토론은 복잡했다.[51][161] 북아메리카 대륙 태평양 해안의 해달이 있지 않는 곳에서도 조개의 수확이 감소하고 있으며, 몇몇 환경보호론자들은 연안에 조개류가 많이 모여 있는 것은 모피 거래로 인한 해달의 지역적 멸종으로 인한 최근의 결과라고 주장한다.[161] 조개의 양에 영향을 미치는 요소는 다양하지만 해달이 조개를 포식함으로써 조개 채취업이 상업상 불가능해질 지경까지 감소할 수 있다.[160] 과학자들은 해달과 전복 채취업이 공존할 수 없다는 데 동의하고 있으며,[160] 그 외의 특정 조개류 역시 동일하다고 간주할 수 있다.[110]

해달과 인간 경제의 상호작용의 여러 양상은 바로 직감하기는 어렵다. 해달은 그 유명한 성게 개체수 조절 기능으로 켈프 수확 산업에 크게 기여한 것으로 생각되고 있으며, 켈프는 음식, 제약 산업 등 다방면으로 사용된다.[162] 인간 잠수부들은 식용 또는 켈프 보호를 위해 붉은성게를 채취하지만 해달은 더 많은 성게 종을 사냥할뿐더러 매우 일관되게 그 개체수를 효율적으로 조절할 수 있다.[163] 켈프림 생태계의 건강은 물고기 개체수의 증가로 이어지며, 인간 경제에 중요한 물고기 종의 개체수도 증가하게 된다.[162] 일부 지역에서는 해달이 관광객들의 인기를 끌어 해달을 보기 위해 찾아오는 사람들로 지역 경제에 도움이 되기도 한다.[162]

인간 문화에서의 역할

AleutKalan1.jpg
Aleut carving of a sea otter hunt

왼쪽: 알류트족의 해달 부적. 새끼를 끌어안은 어미의 모습을 하고 있다. 위쪽: 고래 뼈 창으로 해달을 사냥하는 모습을 묘사한 알류트족의 조각. 둘 다 상트페테르부르크표트르 대제 인류학 및 민족지학 박물관에서 전시 중이다. 해달을 묘사한 물건은 일종의 마술 성질이 있다고 믿어졌다.[164]

북태평양 일대의 해양 토착 문화, 특히 쿠릴 열도아이누 민족, 캄차카반도코랴크인이텔멘인, 알류샨 열도의 알류트족, 하이다과이하이다족,[165] 북아메리카 태평양 해안의 부족들 다수에서 해달은 물질적 자원임과 동시에 문화에도 중요한 역할을 차지했다. 이들 문화권은 대부분 강력한 애니미즘적 전통을 가지고 있으며, 그 전통은 자연 세계의 많은 요소가 정령들과 관련되어 있다는 갖가지 전설과 이야기들로 가득하다. 개중에 해달은 특히 인간과 동질하다고 생각되었다. 누트카족, 하이다족을 비롯해 브리티시컬럼비아 해안 지역의 퍼스트 네이션스들은 따뜻하고 사치스러운 날가죽을 추장의 예장으로서 사용했다. 해달 날가죽은 성년식, 결혼식, 장례식 등의 포틀래치에서 수여되었다.[56] 알류트족은 해달 뼈에 조각을 해서 장식품 또는 놀잇감으로 사용했고, 해달의 음경골을 가루로 만들어 해열제로 사용했다.[166]

아이누 민족에게 수달은 가끔씩 찾아오는 인간과 조물주 사이의 전달자였다.[167] 아이누 민속에서 해달은 반복해 등장한다. 대표적인 아이누 유카르쿠투네 시르카》(クトゥネシㇼカ)는 황금 해달을 둘러싸고 일어나는 전쟁과 다툼을 다룬 서사시이다. 알류트족 사이에는 연인 또는 절망한 여자가 바다 속에 투신하여 해달이 되었다는 전설이 다양한 판본으로 널리 퍼져 있다.[168] 이러한 인간과 해달의 관계는 해달의 여러 가지 인간스러운 행동 특성과 결부지어 생각할 수 있다. 누가 봐도 알 수 있을 정도로 장난기가 많고, 어미와 새끼 사이에 유대감이 강하며, 도구를 사용한다. 그야말로 의인화되기 위해 있는 것 같다고 할 수 있다.[169] 해달에게 상업적 착취가 시작되고, 해달뿐 아니라 아이누와 알류트 역시 쫓겨나고 인구수가 격감했다. 해달의 수가 대폭 감소한 북아메리카 해안의 부족들은 더 이상 생존을 위해 해양 포유류에게 예전같이 의지하지 않았다.[170]

1970년대 이후로는 해달은 그 귀염성과 매력으로 널리 공감을 받게 되었고, 환경 보존 운동의 상징적 존재가 되었다.[154] 해달의 동글동글하고 표현력 풍부한 얼굴, 부드럽고 복슬복슬한 몸은 갖가지 기념품, 엽서, 옷가지, 봉제 장난감 등에서 찾아볼 수 있다.[171]

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벤쿠버 수족관의 해달

수족관과 동물원

해달은 인간에게 잡혀 지내면서도 잘 살 수 있으며, 현재 40개소 이상의 수족관동물원에서 해달을 사육하고 있다.[172] 시애틀 수족관은 1979년에 개체 티추크(Tichuk)가 태어나고, 1980년대에 새끼가 세 마리 더 태어남으로써, 해달을 수정란부터 성체까지 완전히 사육한 최초의 기관이 되었다.[173] 2007년에는 해달 두 마리가 서로 손을 잡고 물에 떠다니는 영상이 유튜브에 업로드되어 2주만에 1백 5십만 회의 조회수를 확보했고, 2013년 기준으로는 1천 9백만 회를 초과하고 있다.[174] 해당 동영상은 벤쿠버 수족관에서 5년 앞서 촬영된 것으로, 업로드되었을 당시 유튜브에서 가장 인기있는 동물 관련 동영상이었다. 동영상에서 털 색깔이 밝은 해달의 이름은 니아크(Nyac)이며, 1989년 엑손 발데스 기름 누출 사건 때 구조된 해달이다.[175][176] 니아크는 2008년 9월에 20살로 죽었다.[177]

같이 보기

각주

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해달: Brief Summary

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해달(한국 한자: 海獺, 학명: Enhydra lutris, sea otter)은 북태평양 북안과 동안에 서식하는 해양 포유류이다. 다 자란 해달의 몸무게는 14-45Kg이며, 이는 족제빗과의 종 중 아주 무거운 편이지만 해양 포유류에 비할 수 없을 만큼 가볍다. 다른 해양 포유류와는 달리 해달의 보온장치는 지방질이 아니라 매우 두꺼운 털가죽이다. 땅에서 걸을 수 있지만 땅을 한 번도 밟지 않고 일생을 보내는 것이 가능하다.

해달은 해안지역에 서식하며 먹이를 위해서는 해면으로 잠수한다. 주식은 성게, 연체동물, 갑각류, 물고기 등이다. 이들의 식성과 먹는 방식은 여러 방면에서 특이하다. 우선 도구를 사용하는 몇 안 되는 동물이라는 점인데 바위를 이용해 조개 등을 깨는 습성에서 볼 수 있다. 서식지에서 해달은 성게 수를 조절하는 데에 중요한 역할을 하며, 이들의 숫자가 줄면 해초 숲이 성게에 의해 초토화될 수도 있다. 해달의 식단 중 인간이 섭취하는 종도 있으므로 어부와의 충돌이 일어나기도 한다.

해달의 개체 수는 털을 위한 남획 전 15만 마리에서 30만 마리였지만 1741년1911년 사이에 이루어진 사냥 때문에 개체 수가 1,000 ~ 2,000마리로 줄었으며 분포지역 또한 줄어들게 되었다. 국제적으로 사냥을 금지하고 재도입 계획으로 개체 수는 늘어나 이제는 한때 차지하던 서식지의 66%를 차지하고 있다. 해달의 회복은 종의 회복에 관한 예를 들 때 캘리포니아의 귀신고래와 함께 성공 사례로 거론된다. 하지만 알류샨 열도캘리포니아의 해달 개체군은 감소하는 등 아직도 위험에 놓여 있다. 이러한 이유로 해달은 여전히 멸종 위기종으로 분류되고 있다.

license
ko
copyright
http://creativecommons.org/licenses/by-sa/3.0/

Habitat

provided by World Register of Marine Species
shallow, nearshore waters
license
cc-by-4.0
copyright
WoRMS Editorial Board
bibliographic citation
van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).
contributor
Jacob van der Land [email]
contributor
Jacob van der Land [email]