Enhydra lutris - (Linnaeus, 1758)
Sea Otter
Taxonomic Status: Accepted
Related ITIS Name(s): Enhydra lutris (Linnaeus, 1758) (TSN 180547)
French Common Names: loutre de mer
Unique Identifier: ELEMENT_GLOBAL.2.102244
Element Code: AMAJF09010
Informal Taxonomy: Animals, Vertebrates - Mammals - Carnivores
Image 7708

© Larry Master

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Mammalia Carnivora Mustelidae Enhydra
Genus Size: A - Monotypic genus
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Concept Reference
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Concept Reference: Wilson, D. E., and D. M. Reeder (editors). 1993. Mammal species of the world: a taxonomic and geographic reference. Second edition. Smithsonian Institution Press, Washington, DC. xviii + 1206 pp. Available online at: http://www.nmnh.si.edu/msw/.
Concept Reference Code: B93WIL01NAUS
Name Used in Concept Reference: Enhydra lutris
Taxonomic Comments: There has been some disagreement as to whether the recognition of subspecies is warranted (see reviews by Wilson et al. 1991 and Bodkin and Kenyon 2003). A recent range-wide review of geographic variation of skull characters concluded that three subspecies should be recognized: E. lutris lutris from Asia to the Commander Islands, E. l. nereis in California, and E. l. kenyoni in Alaska (Wilson et al. 1991). The subspecific taxonomy suggested by morphological analyses is largely but not completely supported by subsequent molecular genetic data. Analysis of mitochondrial DNA (mtDNA) variation among eight geographically isolated populations identified four major groups (Cronin et al. 1996, Scribner et al. 1997). The haplotype frequency in the Commander Island population of E. l. lutris is more similar to that observed in the Aleutian-Kodiak grouping, E .l. kenyoni, than to the Asian populations of subspecies E. l. lutris, with which it was aligned by skull morphology. Additionally, the Prince William Sound population differs from the other Alaska populations in haplotype frequency. Subspecies nereis appears to have monophyletic mtDNA, but lutris and kenyoni do not (Cronin et al. 1996). The low level of divergence of sequences of haplotypes on mtDNA suggests that there are no major phylogenetic breaks or long-term barriers to gene flow among sea otter populations (Cronin et al. 1996).

Lidicker and McCollum (1997) examined allozyme variation and found that despite historical population depletion, otters from California have suffered only a small loss in genetic variability. MtDNA data also indiciate that population bottlenecks probably did not result in major losses of genetic variation in individual populations or the species as a whole (Cronin et al. 1996). However, based on microstatellite DNA and mtDNA, Larson et al. (2002) reported that the levels of genetic diversity observed within sea otter populations were relatively low when compared with other mammals and may be the result of fur trade exploitation.
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 04Apr2016
Global Status Last Changed: 18Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G4 - Apparently Secure
Reasons: Large range in North Pacific; total population has increased to more than 100,000 (430 in Washington); subject to intensive management; vulnerable to oil spills and conflicts with commercial fisheries.
Nation: United States
National Status: N4 (05Sep1996)
Nation: Canada
National Status: N3 (29Dec2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alaska (S4), California (SNR), Oregon (SH), Washington (S2)
Canada British Columbia (S3)

Other Statuses

Implied Status under the U.S. Endangered Species Act (USESA): PS
Comments on USESA: Subspecies nereis of California is listed by USFWS as Threatened, except in areas subject to U.S. jurisdiction south of Pt. Conception, California, where status is governed by Public Law 99-625, 100 Stat. 3500 (experimental nonessential population). The southwest Alaska DPS of E. l. kenyoni is listed threatened under the Endangered Species Act (Federal Register, 9 August 2005).
Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: SC (05Jun2003)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Special Concern (22Apr2007)
Comments on COSEWIC: Reason for Designation: The species had been extirpated in British Columbia by the fur trade by the early 1900s, and was re-introduced from 1969-72. It has since repopulated 25-33% of its historic range in British Columbia, but is not yet clearly secure. Numbers are small (<3,500) and require careful monitoring. Their susceptibility to oil and the proximity to major oil tanker routes make them particularly vulnerable to oil spills.

Status History: Designated Endangered in April 1978. Status re-examined and confirmed Endangered in April 1986. Status re-examined and designated Threatened in April 1996 and in May 2000. Status re-examined and designated Special Concern in April 2007. Last assessment based on an update status report.

IUCN Red List Category: EN - Endangered
Convention on International Trade in Endangered Species Protection Status (CITES): Appendix II

NatureServe Global Conservation Status Factors

Range Extent: 20,000-2,500,000 square km (about 8000-1,000,000 square miles)
Range Extent Comments: Nearshore waters of the Northern Pacific Ocean. Subspecies lutris: northwestern Pacific, from the Kiritappu Peninsula of eastern Hokkaido Island (formerly) and Kurile Islands to Commander Islands. Subspecies kenyoni: Aleutian Islands, southern Alaska, British Columbia, and Washington; extirpated and later reintroduced in southeastern Alaska, British Columbia, and Washington; extirpated and unsuccessfully reintroduced in the Pribilof Islands and Oregon. Subspecies nereis: California coast, mainly from Santa Cruz to Pismo Beach; formerly south to Morro Hermoso, Baja California, and throughout the Channel Islands; recently reintroduced to San Nicolas Island; see Rodriguez-Jaramillo and Gendron (1996) for an occurrence off southern Baja California. See Gallo-Reynoso and Rathbun (1997) for a discussion of possible occurrences off Baja California.

Number of Occurrences: 81 to >300

Population Size: 10,000 to >1,000,000 individuals
Population Size Comments: Estimates from the mid- to late 1980s suggested populations of 6000-7000 in the Kuril Islands, 2000-2500 in the Commander Islands, and 2500-3000 off Kamchatka, giving a total western Pacific population of 10,500-12,500 (Riedman and Estes 1990, Reeves et al. 1992). In the 1980s, the total population from Prince William Sound to the Kuril Islands was about 150,000 (Riedman 1990). For the Aleutian Islands, the minimal population estimate was 8,742 sea otters in 2000 (Doroff et al. 2003).

Alaska had 100,000-150,000 in the mid- to late 1980s (Reeves et al. 1992), and the current population probably also is in this range (USFWS 1995 stock assessment). Prince William Sound population in late 1980s was about 14,000, of which an estimated 2800 were killed as a result of the Exxon Valdez oil spill (Raloff 1993). From an original 402 individuals translocated in the 1960s, the population in southeastern Alaska increased to more than 3500 in five populations by 1987 (Reeves et al. 1992); 1988 estimate was 4520 (See Riedman and Estes 1990).

In 1984, the population off west coast of Vancouver Island, British Columbia, was 345 (descended from 89 that were translocated from Alaska, 1969-1972) (MacAskie 1986); 1987 count was 380 (see Riedman and Estes 1990). In 1995, the minimum number along the coast of British Columbia was 1522, including 135 near Goose Island (Watson et al. 1997).

Otters were transplanted from Alaska to Washington in 1969 and 1970; population increased from 36 to 94 between 1981 and 1987 (Matthews and Moseley 1990); 211 were counted in Washington in July 1989 (Jameson, in Riedman and Estes 1990, Reeves et al. 1992).

See also record for subspecies nereis of California (about 2,505 individuals in 2003).

Overall Threat Impact Comments: In various parts of the range, conflicts with commercial fisheries (gill and trammel nets, crab traps) and activities associated with oil and gas exploration, development, and transportation may be the greatest threats. Commercial fisheries are not a threat in Alaska (USFWS 1995 stock assessment). Brody et al. (1996) determined that an oil spill of Exxon Valdez size, occurring at the Monterey Peninsula, California, would kill at least 50% of the total California sea otter population.

In the Aleutian Islands in recent decades, the population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. These data are in general agreement with the hypothesis of increased predation on sea otters (Doroff et al. 2003). Killer whales presumably shifted their diet to include sea otters after populations of their preferred prey, harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), declined.

Short-term Trend: Increase of >10%
Short-term Trend Comments: Washington population started with 59 individuals translocated from Alaska in 1969-1970; increasing--spring 1996 survey yielded 430 individuals (USFWS 1997 draft revised stock assessment).

Long-term Trend:  
Long-term Trend Comments: In the Aleutian Islands, the number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. The population decline likely began in the mid-1980s and declined at a rate of 17.5% per year in the 1990s (Doroff et al. 2003). These data chronicle one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history (Doroff et al. 2003).

Other NatureServe Conservation Status Information

Protection Needs: See the 1996 Endangered Species Update 13(12) for 20 articles dealing with sea otter conservation and management.

Distribution
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Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Nearshore waters of the Northern Pacific Ocean. Subspecies lutris: northwestern Pacific, from the Kiritappu Peninsula of eastern Hokkaido Island (formerly) and Kurile Islands to Commander Islands. Subspecies kenyoni: Aleutian Islands, southern Alaska, British Columbia, and Washington; extirpated and later reintroduced in southeastern Alaska, British Columbia, and Washington; extirpated and unsuccessfully reintroduced in the Pribilof Islands and Oregon. Subspecies nereis: California coast, mainly from Santa Cruz to Pismo Beach; formerly south to Morro Hermoso, Baja California, and throughout the Channel Islands; recently reintroduced to San Nicolas Island; see Rodriguez-Jaramillo and Gendron (1996) for an occurrence off southern Baja California. See Gallo-Reynoso and Rathbun (1997) for a discussion of possible occurrences off Baja California.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AK, CA, OR, WA
Canada BC

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
CA Marin (06041), Ventura (06111)
WA Clallam (53009), Grays Harbor (53027), Jefferson (53031)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
17 Hoh-Quillayute (17100101)+, Queets-Quinault (17100102)+, Crescent-Hoko (17110021)+
18 San Pablo Bay (18050002)+, San Pedro Channel Islands (18070107)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A marine mammal (sea otter), to about 1.5 m long.
General Description: Pelage thick, mainly reddish, dark brown, or black, with the head whitish in older individuals, especially males; tail thick (to about 35 cm), about 1/4 of body length; hind feet flattened and webbed, outer toe longest, with vestigial leathery foot pads; front feet relatively small and round; ear pinnae small; to about 1.5 m in total length; adult males usually 25-40 kg, females usually 15-25 kg.
Diagnostic Characteristics: Differs from pinnipeds in longer tail and much smaller forelimbs that are not flipperlike. Differs from the river otter in shorter tail and flipperlike hind feet. This is the only carnivore with 2 pairs of lower incisors (all others have 3 pairs).
Reproduction Comments: Strongly polygynous. Reproduction is weakly seasonal. Births in spring and summer with peak in early summer in Alaska (late May in Prince William Sound); peak December-March (generally late winter) in California. Implantation delayed, gestation about 8-9 months in Alaska, about 4-6 months in California. Young dependent on mother for about 6-7 months in California, 76-333 days (average 170) in Prince William Sound, Alaska. In California, adult females generally give birth to 1 pup every year; females in some areas of Alaska give birth every other year. In California, females sexually mature usually in 3-5 years. In Alaska, 30% of females were sexually mature at age 2, 100% by age 5; annual reproductive rates increased from 22% at age 2 to 78% at age 5 and remained relatively stable (75-88%) through age 15 (Bodkin et al. 1993). Commonly lives 10-15 years; maximum known ages are 23 years for females and 18 years for males.
Ecology Comments: Keystone predator; often limits prey populations; predation on herbivores determines structure of off-shore kelp communities (e.g., Estes et al. 1989).

Males defend contiguous territories from which they exclude other males (Riedman and Estes 1990).

Males may move up to 30-60 miles along coast, females generally stay within area 5-10 miles long. Daily movements generally encompass a few kilometers (Riedman and Estes 1990). Ralls et al. (1996) found that otters in California usually were within 1-2 km of their location on the previous day but often stayed in one place for an extended period then suddenly moved a much greater distance; the area used by individual otters during a single 24-hour period was 7-1166 ha.

Undisturbed populations can increase at about 17-20%/year, although the central California population never has increased at more than 5-7%/year (Riedman and Estes 1990).

Habitat Type: Marine
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Seasonal movements occur among some age-sex classes in certain areas (Riedman and Estes 1990).
Marine Habitat(s): Near shore
Estuarine Habitat(s): Bay/sound, Tidal flat/shore
Special Habitat Factors: Benthic
Habitat Comments: Coastal waters usually within 2 km of shore, especially shallows with kelp beds and abundant shellfish. In rough weather, takes refuge among kelp, or in coves and inlets. Often comes ashore in Alaska, rarely does so in California. In California, juvenile males spend little time in near-shore kelp beds; often remain far offshore (Siniff and Ralls (1988). In California, young are born in the water or on land; births may usually occur ashore in Alaska.
Adult Food Habits: Invertivore, Piscivore
Immature Food Habits: Invertivore, Piscivore
Food Comments: Diet varies according to location; often dominated by benthic invertebrates. Sea urchins, crabs, and a variety of molluscs are principal foods, but fish are important food items at high population densities. Forages usually at depths of less than 20 m. Uses rocks or other hard objects as tools to break exoskeletons of invertebrate prey. Diets and patterns of foraging behavior may be highly individualized (Riedman and Estes 1990).
Adult Phenology: Circadian
Immature Phenology: Circadian
Phenology Comments: Foraging occurs throughout the day and night, with periodic resting in between feeding bouts.
Length: 150 centimeters
Weight: 35000 grams
Economic Attributes
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Economic Comments: Negatively impacts shellfisheries, though the degree of impact is controversial.
Management Summary
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Stewardship Overview: See 1995 draft recovery plan for the California population.
Restoration Potential: Recovery potential is high if environmental conditions are favorable. In Alaska, otters at the leading edge of an expanding population in an area with abundant food resources and protected water exhibited high adult survival rate, high reproductive rate, and high preweaning survival (Monson and DeGange 1995). Human harvest was the primary source of known mortality of adults.
Management Requirements: See the 1996 Endangered Species Update 13(12) for 20 articles dealing with sea otter conservation and management.

Brody et al. (1996) reviewed the EXXON VALDEZ oil spill and concluded that efforts to rehabilitate otters should be discontinued 20-30 days after a spill.

Draft revised recovery plan for California populations was available in February 2000 (contact U.S. Fish and Wildlife Service, Ventura, California).

Monitoring Requirements: See the 1996 Endangered Species Update 13(12) for articles dealing with sea otter conservation and management, including monitoring.
Population/Occurrence Delineation
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Use Class: Not applicable
Minimum Criteria for an Occurrence: Evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Upland areas.
Separation Distance for Unsuitable Habitat: 50 km
Separation Distance for Suitable Habitat: 50 km
Alternate Separation Procedure: Where an occurrence is at least twice the size of a minimum A-ranked occurrence, it may be divided into two or more A-ranked occurrences along divisions that are narrower (or absent) than the separation distances given. The dividing lines should be made as much as possible through regions of limited Sea Otter use.
Separation Justification: Separation distance somewhat arbitrary; based on female, rather than more extensive male movements. Annual movements of males cover 50-100 kilometers; females move about 8-16 kilometers (Riedman and Estes 1991).
Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 16 km
Inferred Minimum Extent Justification: Based on annual movements of females (Riedman and Estes 1990).
Date: 16Aug2001
Author: Cannings, S.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 08Mar2005
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 02May1995
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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