Enhydra lutris 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Mustelidae

Scientific Name: Enhydra lutris (Linnaeus, 1758)
Common Name(s):
English Sea Otter
French Loutre de mer
Spanish Nutria del Kamtchatka, Nutria Marina
Mustela lutra Linnaeus, 1758
Taxonomic Notes: Three regional subspecies have been confirmed by Cronin et al. (1996); E. l. lutris (Linnaeus, 1758) from the Asian range of the Kuril Islands southeast to the Kamchatka Peninsula and the Commander Islands, E. l. kenyoni Wilson, 1991 from the Aleutian Islands to Prince William Sound, Alaska, USA, along the Pacific coast of Canada and into Oregon state in the continental USA, and E. l. nereis (Merriam, 1904) from central California, USA.

Assessment Information [top]

Red List Category & Criteria: Endangered A2abe ver 3.1
Year Published: 2015
Date Assessed: 2013-01-05
Assessor(s): Doroff, A. & Burdin, A.
Reviewer(s): Hussain, S.A. & Duplaix, N.
This species is considered to be Endangered under criterion A2abe based on past large-scale population declines. The species is believed to have undergone a decline exceeding 50% over the past 45 years (three generations based on Pacifici et al. 2013). The world-wide population of Sea Otters decreased to approximately 2,000 animals by the end of the commercial fur trade in 1911 (Kenyon 1969). The population recovered from 11 remnant subpopulations located in Russia (Bering Island, Kamchatka Peninsula, and Kuril Islands) and in the United States (in Alaska (Aleutian Islands, Alaska Peninsula, Kodiak archipelago, and Prince William Sound) and California). The remnant subpopulations were small and widely dispersed, as a result, this species has low genetic diversity (Ralls et al. 1983). Since the 1980s, the species had been recovering in many areas thanks to intensive management and regulatory efforts by several governments. However contemporary issues (oil spills, potential fisheries interactions, predation, and disease events), have either prevented Sea Otter populations from thriving or have caused population declines throughout much of the species range. In the United States, two subspecies of Sea Otters are listed as threatened (E. lutris kenyoni in SW Alaska and E. lutris nereis in California) due to precipitous population declines in Alaska and slow growth (and vulnerability to anthropogenic factors) of a small subpopulation in California.

In Alaska, precipitous population declines occurred in the Aleutian Islands beginning in the late 1980s-2005. By 2000, counts of Sea Otters had decreased by 90% with a declining trend through 2005 (Doroff et al. 2003, Estes et al. 2005, Burn et al. 2003). The probable cause of the decline was increased predation by Killer Whales (Orcinus orca) (Estes et al. 1998).  More recent Sea Otter surveys indicate the population trend has increased since 2005, however, counts remain well below carrying capacity for this region (D. Burn pers. comm. 2010). Population counts also remain low for the Alaska Peninsula (Burn and Doroff 2005, U.S. Fish and Wildlife Service Stock Assessment Reports). The subpopulation in the Kodiak archipelago and lower Cook Inlet appeared stable or increasing during the same period that population declines were documented in the Aleutian Islands and Alaska Peninsula (Kodiak and lower Cook Inlet are part of the Southwest population stock), however, this habitat has not been surveyed since 2004.

Recent studies have found infectious disease to be an important mortality factor in the California Sea Otter subpopulation (Conrad et al. 2005, Johnson et al. 2009). Information collected from forensic-level necropsies of dead Sea Otters and sampling of free-ranging Sea Otters indicate a strong link to protozoan parasites, Toxoplasma gondii and Sacrocystis neurona, that are known to breed in cats and opossums (Thomas and Cole 1996, Conrad et al. 2005) thus sources of mortality for the Sea Otter population include land-based factors. Other factors identified as causing significant mortality include acanthocephalan peritonitis, protozoal encephalitis, bacterial and fungal infections (Thomas and Cole 1996).

We have more population information from Russian now than in previous assessments. The number of Sea Otters along the Commander Islands reached maximum since last 150 years period (A. Burdin and Zagrebelny pers. comms. 2006). In 2007, the direct count revealed around 8,000 otters in both Bering and Medny Islands. The Commanders Island subpopulation of Sea Otter was never so abundant, but in 2008, it was found that the population was in decline and more recent estimates indicate the population to be 5,500. In 2004 the Kuril Islands subpopulation of Sea Otter was estimated around 19,000 (Kornev and Korneva 2006), but later counts have shown severe declines (up to 40-50% in different locations). Though the causes of these declines are not very clear, the threat due to poaching can’t be ruled out.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

Historically, Sea Otters occurred across the North Pacific Rim, ranging from Hokkaido, Japan, through the Kuril Islands, the Kamchatka Peninsula, the Commander Islands, the Aleutian Islands, peninsular and south coastal Alaska and south to Baja California, Mexico (Kenyon 1969). In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). Although it appears that harvests periodically led to local reductions of sea otters (Simenstad et al. 1978), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969).  Remnant populations were located in the Kuril Islands, Kamchatka and in the Commander Islands Russia; five in southwestern Alaska (the Aleutian Islands, Alaska Peninsula, and Kodiak Island), and one remnant population in each of the following regions; south-central Alaska (Prince William Sound), Canada (Queen Charlotte Islands), central California, and Mexico (San Benito Islands) (Estes 1980). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter subpopulations have presumably died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

In North America, the Sea Otter’s range is currently fairly continuous from the Aleutian Islands to Prince William Sound with population gaps along the Gulf of Alaska until Yakutat (which was a translocated population) with another gap in the population’s distribution until the outer islands of southeast Alaska (also a translocated subpopulation from the Aleutian Islands and Prince William Sound). The next gap in the Sea Otter population distribution is between southeast Alaska and British Columbia, Canada.  Translocation efforts were successful in Washington State but not in Oregon thus there is a large population gap between the small Sea Otter subpopulation in Washington and that of central California.
Countries occurrence:
Canada; Japan; Mexico; Russian Federation; United States
FAO Marine Fishing Areas:
Atlantic – northwest
Additional data:
Lower depth limit (metres):82
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982), occurring along the North Pacific from northern Japan to the central Baja Peninsula in Mexico. Its abundance was greatly reduced by human exploitation. Although it appears that harvests periodically led to local reductions of sea otters (Simenstad et al. 1978), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969): two in the Kuril Islands and Kamchatka; one in the Commander Islands; a total of 10 in the following areas: Aleutian Islands (2) and along the Alaska Peninsula (3); Kodiak Island (1), Prince William Sound (1), the Queen Charlotte Islands (1), central California (1), and San Benito Islands (1). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter subpopulations have died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

Sea Otters currently have established populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, and there have been reports of single-animal observations in Mexico and Japan. Population estimates made between 2004 and 2012 give a worldwide total of approximately 125,831 Sea Otters. In Russia, the most recent population estimates are from 2004 at which time reported counts were about 19,000 are in the Kurils, 3,500 on the Kamchatka Peninsula and another 5,500 on the Commander Islands.  The Sea Otter population in Alaska was estimated at between 100,000 and 125,000 individuals in 1973. In 2013, the estimated population is 89,073 animals in Alaska. In southwest Alaska, the population stock is listed as Threatened under the Endangered Species Act (ESA) and a strategic stock under the Marine Mammal Protection Act (MMPA). There are low densities of Sea Otters from Castle Cape (south Alaska Peninsula) to Attu Island (Aleutian Island chain) and the population no longer functions as a key stone species in the habitat.  Moderate densities are found from Castle Cape to Kamishak Bay (inclusive of the Kodiak Archipelago) and numbers are stable or slightly increasing.  There is no evidence of further population decline but also no evidence of recovery. In south-central Alaska, the Sea Otter population stock is not a strategic stock under MMPA. Overall the population in this region is stable or slightly increasing. During 2012-2017, the federal government is soliciting an oil and gas lease sale that may impact the SW & SC population stocks. In southeast Alaska the Sea Otter population stock, is not a strategic stock under MMPA.  Population range expansion is expected to continue in this region, however, population growth rates have been lower than predicted for the region.  Legal and illegal harvest may be contributing factors to the slow growth.  There are heightened conflicts with commercial dive fisheries in this region.  Recent clarifications were made to the MMPA definition of “significantly altered” for Native handicrafts made from Sea Otter fur by the U.S. Fish & Wildlife Service.  Elected Alaska leadership explored placing a bounty on sea otter pelts to help reduce the Sea Otter population in order to protect shell fisheries.  Along the North American coast south of Alaska, the Sea Otter's range is discontinuous. Between 1969 and 1972, 89 Sea Otters were shipped from Alaska to the west coast of Vancouver Island, British Columbia Canada. They established a healthy population, estimated to be 4,712 as of 2011, and their range is now from Tofino to Cape Scott. In 1969 and 1970, 59 Sea Otters were translocated from Amchitka Island to Washington State; the population estimate in 2012 was 1,105 individuals, and their range is in the Olympic Peninsula from just south of Destruction Island to Pillar Point. In Washington State, the Sea Otter population is listed as Endangered under Washington State’s Endangered Species Act.  Population growth is expected to continue in this region.  In California, the 2013 population estimate was 2,941; counts are down from an estimated pre-fur trade population of 16,000 (USGS unpublished data). California's Sea Otters are the descendants of a single colony of about 50 southern Sea Otters discovered near Big Sur in 1938; their principal range is now from just south of San Francisco to Santa Barbara County. The southern Sea Otter is listed as Threatened under the Endangered Species Act (ESA) and a strategic stock under the MMPA. This population is also listed as “fully protected” under State law in California.  The population has been numerically stable for the past 5-6 years with a low annual growth rate of <1%/yr.  There have been increased shark related mortalities in the southern part of the range and mortality from shark bites is the primary known cause of mortality at this time.  The Southern Sea Otter Translocation programme was recently terminated and the subpopulation on San Nicolas Island is no longer considered experimental.

In summary, population range expansion continues for translocated sea otters in B.C.,Canada, Washington, and SE Alaska but at diminished rates of increase from the previous decade. The cause(s) of the reduced population growth rates are unclear at this time. The Sea Otter population recovery in the Endangered Species Act listed areas of California and SW Alaska are still a major concern for the species as a whole. Reports of declining trends in Sea Otter abundance along the Kamchatka Peninsula and Kuril islands in Russia are also a major concern and require further investigation.
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Throughout their range, Sea Otters use a variety of near shore marine environments and 84% of foraging occurs in water ≤ 30m in depth (Bodkin et al. 2004) and throughout much of their range, foraging occurs within a kilometre of the shore. Their classic association is with rocky substrates supporting kelp beds, but they also frequent soft-sediment areas where kelp is absent (Riedman and Estes 1990, DeMaster et al. 1996, Burn and Doroff 2005). Kelp canopy is an important habitat component, used for foraging and resting (Riedman and Estes 1990). 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. 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. Individuals generally occupy a home range a few kilometres long, and remain there year-round. Sea Otters forage in rocky and soft-sediment communities on or near the ocean floor. The maximum confirmed depth of dive was 97 m (Newby 1975); however, recent studies using time-depth recorders implanted in Sea Otters indicate average maximum forage depths of 54 m for female and 82 m for male sea otters (Bodkin et al. 2004).

Sea Otters are weakly territorial (Kenyon 1969) with fighting and aggression rare (Loughlin 1980). Only adult male Sea Otters establish territories. Males patrol territorial boundaries and attempt to exclude other adult males from the area. Females move freely between and among male territories. Groups of male and female sea otters generally rest separately. Sea Otter annual home ranges can occupy up to 0.8 km² (80 ha) and extend along 16 km of coastline (Kenyon 1969, Loughlin 1980). Typically, female Sea Otter home ranges are about 1.5-2 times larger than resident adult males during the breeding season; however, females have smaller annual or lifetime home ranges than males (Riedman and Estes 1990). Jameson (1989) found that territorial adult males occupied a mean home range of 40.3 ha during the summer-fall period (when home range size was considered equal to territory size); and mean coastline length was 1.1 km. Winter-spring mean home range size of territorial adult males that remained in female areas was 78.0 ha, with a mean coastline length of 2.16 km.

The diet of Sea Otter consists almost exclusively of marine invertebrates, including sea urchins, a variety of bivalves such as clams and mussels, abalone, other molluscs, crustaceans, and snails. Its prey ranges in size from tiny limpets crabs and giant octopuses (Estes 1980). Sea urchins, abalones and rock crabs are the principal prey of Sea Otters in newly reoccupied habitats of central California (Vandevere 1969) whereas clams and crab will make up the diet in soft-sediment habitats (Kvitek et al. 1992, Doroff and DeGange 1994). 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 (Kvitek et al. 1992). In California, it has been noted that Sea Otters ignore Pismo Clams smaller than three inches (7 cm) across. Only in the Aleutian archipelago were Sea Otters observed to regularly eat fish, which could comprise up to 50% of their diet. The fish species eaten were usually bottom dwelling and sedentary or sluggish forms, such as the Red Irish Lord and Globefish (Estes 1980). They also consume crab, clam, mussels, turban snails, sea cucumbers, squid, octopus, chitons, tubeworms, large barnacles, scallops, and sea stars (Wild and Ames 1974, Riedman and Estes 1990). Bivalve molluscs are excavated by digging in sand or mud bottoms and are the most common prey in soft-sediment communities (Calkins 1978, Kvitek et al. 1992, Doroff and DeGange 1994).

Male Sea Otters reach sexual maturity around age five or six, but probably do not become territorial or reproductively successful for two or three subsequent years (Riedman and Estes 1990). Most female Sea Otters are sexually mature at age four or five though some are mature as early as 2.5 years (Kenyon 1969, Jameson and Johnson 1993, Monson et al. 2000, Monson and DeGange 1995, von Biela 2007). Sea otters apparently are polygynous, although the exact nature of the mating system may vary. Females normally give birth to a single pup that weighs 1.4 to 2.3 kg at birth (Riedman and Estes 1990). Twinning has been documented in Sea Otters (Williams et al. 1980); however, litters larger than one are rare, and when they occur, neither pup is likely to survive (Jameson and Bodkin 1986). Pups remain dependent upon their mothers for about six months (Jameson and Johnson 1993). Longevity in Sea Otters is estimated to be 15 to 20 years for females and 10 to 15 years for males (Riedman and Estes 1990).
Systems:Terrestrial; Marine
Generation Length (years):15

Use and Trade [top]

Use and Trade: Information pertaining to Sea Otter trade has been taken from  Europeans and Americans first ventured to the North Pacific coast of America in the late eighteenth century in pursuit of Sea Otter skins. As the Pacific counterpart to the Atlantic Beaver trade, the Sea Otter trade led trappers into the North Pacific, where they established bases from the Aleutian Islands to Baja California. In China, Sea Otter furs were exchanged at good profit for prized Oriental goods.

Russia and Spain were the pioneer nations to engage in the Sea Otter trade. After Vitus Bering's expeditions in the early eighteenth century, promyshlenniki (fur traders) pushed eastward, and in 1784 they established the first permanent Russian settlement in America, on Kodiak Island. In the same year, Spain organized a Sea Otter trade between California and China. At the opening of the nineteenth century, American and Russian traders entered the California Sea Otter fields, where in the face of strong opposition they poached throughout the Spanish period. After 1821 the liberal commercial policy of independent Mexico stimulated the California Sea Otter trade, and many Americans became Mexican citizens to participate in the business. Between 1804 and 1807 it is estimated that almost 60,000 furs were taken by American vessels, while the period 1808–1812 yielded nearly 50,000.

The Sea Otter trade ended once hunting nearly exterminated the animals. In general, the fur areas were exhausted in the order they were opened. Kamchatka and the Aleutians were depleted by 1790, Kodiak by 1805, Sitka to Nootka Sound by 1820, and California by 1840. A treaty signed in 1910 by the United States, Great Britain, Russia, and Japan banned the hunting of Sea Otters. However, Sea Otter trade still exists. Sea Otter pelts are also being sold in Russia, with at least 300 skins being sold on the black market in Moscow in summer 2005. Most of these were obtained illegally from the Commander Islands Biosphere Nature Reserve. Since then we have been informed that a further 300 Sea Otter skins were being sold openly on the black market at Petropavlovsk-Kamchatskiy, with 200 of them from the Commander Islands. Most of these skins will be sold on to the markets in China (IOSF 2006).

In Alaska the Marine Mammal Protection Act allows for coastal Native people to hunt northern Sea Otters for subsistence use (personal uses and barter or trade of unaltered pelts with other Native people), and for creating and selling authentic handicrafts or clothing provided the taking was not wasteful; there is no other legal harvest of Sea Otters.  The harvest of Sea Otters is monitored by the U.S. Fish and Wildlife Service’s Marking, Tagging and Reporting programme and all pelts are required to be tagged within 30 days of the hunt. The five year mean of the annual harvest reported to the Service for all three population stocks totalled  765 Sea Otters (U.S. Fish and Wildlife Service Stock Assessment Reports

Threats [top]

Major Threat(s): Oil spills are the greatest anthropogenic threat to Sea Otter (Geraci and Williams 1990). Sea Otters become hypothermic when oiled because oiled Sea Otter fur loses its insulative property and Sea Otters have no blubber layer, oil can be ingested while grooming, leading to gastrointestinal disorders, other ailments and death and volatile components of oil inhaled by Sea Otters can cause lung damage. Estimates of Sea Otter mortality following the Exxon Valdez spill in Prince William Sound ranged from 2,650 (Garrott et al. 1993) to 3,905 (DeGange et al. 1994).

Significant numbers of Sea Otters drowned in gill and trammel nets in California from the mid-1970s to the early 1980s (Estes 1990). Recent population declines in California’s Sea Otters may be incidental to summer commercial fisheries. Estes et al. (2003) found that Sea Otter mortality was elevated in the summer months and that commercial fin fish landings in the coastal live trap fishery increased. Recent analyses indicated annual Sea Otter carcass recoveries and reported fishery landings were significantly correlated.

Thomas and Cole (1996) found 10% of southern Sea Otters they examined to be emaciated without specific cause of mortality. Severe weather and periodic climatic events such as El Niño can disrupt foraging behaviour and food availability, and increase pup loss. Under these circumstances, sea otters may find it difficult to meet their high metabolic needs, leading to malnutrition or starvation. Serious tooth wear in older sea otters may also contribute to mortality (Riedman and Estes 1990). Recent studies have found infectious disease to be an important mortality factor in California Sea Otter populations. Around 280 Sea Otters found dead have been linked “to a pair of protozoan parasites, Toxoplasma gondii and Sacrocystis neurona, that are known to breed in cats and opossums (Conrad et al. 2005, Johnson et al. 2009). In Alaska, Streptococcal endocarditis, encephalitis and/or septicaemia, referred to as Strep. syndrome has been identified in forensic-level necropies of northern Sea Otters (Unusual Mortality Event Working Group) as well as trauma from boat strikes.  Goldstein et al. (2009) found northern Sea Otters from the Alaska Peninsula, Kodiak and Kachemak Bay area infected with phocine distemper.

Killer Whales (Orcinus orca), Great White Sharks (Carcharodon carcharias), Bald Eagles (Haliaeetus leucocephalus), Coyotes (Canis latrans), and Brown Bears (Ursus arctos) have been documented as predators of Sea Otters (Riedman and Estes 1990). Predation by Killer Whales is one factor that is believed to have caused Sea Otter population declines across the Western Gulf of Alaska and Aleutian Islands (Doroff et al. 2003, Estes et al. 1998, Hatfield et al. 1998). Significant declines in preferred prey species populations - Northern Fur Seals (Callorhinus ursinus), Harbour Seals (Phoca vitulina), and Steller Sea Lions (Eumetopias jubatus) are believed to have caused Killer Whales to prey switch and consume Sea Otters (Estes et al. 1998).

Other potential threats to Sea Otters come under the climate change umbrella and include: ocean acidification in the north Pacific, pathogen transport, marine invasive species, biotoxins sequestered  in bivalve prey, and frequency and intensity of storm events.

Conservation Actions [top]

Conservation Actions: Enhydra lutris nereis is listed on CITES Appendix I. All other subpopulations are included on CITES Appendix II. In Canada, Sea Otters are protected and managed under the Species at Risk Act. In the United States, Sea Otters are protected by the Marine Mammal Protection Act of 1972 (MMPA) and in southwest Alaska and California, the Endangered Species Act of 1973 (ESA). The U.S. Fish and Wildlife Service (Service) is the federal agency responsible for their conservation and management. The ESA also makes it illegal to buy, sell or possess any part of endangered species or items made from them. However, both the ESA and the Act allow for coastal Native people in Alaska to harvest Sea Otters for personal use, trade, barter, and the development of cottage industry. Native subsistence harvest of Sea Otters is monitored by the Service through a Marking, Tagging and Reporting programme. The Service and Native organizations conduct joint population surveys and dialogue on important conservations issues. The MMPA also mandates that efforts must be made to recover the species, which means creating and implementing a plan for returning them to healthy population levels.

In southeast Alaska, there are strong pressures to develop incentives to increase levels of Sea Otter hunting and marketing of pelts in order to decrease the population. Any such actions should be considered very carefully in light of climate change stressors, such as ocean acidification, and historic population patterns for this species.  It was the commercial value of Sea Otter pelts that lead to a near extinction of the species; the global market still exists for Sea Otter and all other 12 species of otter pelts. While the MMPA provides for cottage industry of Sea Otter fur products of coastal Alaska Native people, this specific exemption is not designed to manage the harvested populations and must proceed in a manner which would prevent illegal trade for Sea Otter pelts. Past history so dramatically illustrated the vulnerability of Sea Otters to over-harvest.

Citation: Doroff, A. & Burdin, A. 2015. Enhydra lutris. The IUCN Red List of Threatened Species 2015: e.T7750A21939518. . Downloaded on 22 September 2018.
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