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BC Conservation Data Centre: Species Summary


Enhydra lutris
Sea Otter

 
Scientific Name: Enhydra lutris (Linnaeus, 1758)
English Name: Sea Otter
 
Classification / Taxonomy
Scientific Name - 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/.
Classification Level: Species
Species Group: Vertebrate Animal
Species Code: M-ENLU
Kingdom Phylum Class Order Family
Animalia Craniata Mammalia Carnivora Mustelidae
   
Conservation Status / Legal Designation
Global Status: G4 (Apr 2016)
Provincial Status: S3S4 (Jan 2022)
BC List: Blue
Provincial FRPA list:   
Provincial Wildlife Act: Threatened
COSEWIC Status: Special Concern (May 2022)
SARA Schedule: 1  -  Special Concern (Mar 2009)
General Status Canada:
   
Ecology & Life History
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.
Subspecies Comments: Enhydra lutris kenyoni is the only subspecies of sea otter occurring in British Columbia (Watson et al. 1997; Wilson et al. 1991).
Identification Comments: Sea otters are the largest North American mustelid, but the smallest marine mammal found in British Columbia. They are distinguished from river otters (Lontra canadensis) by their larger size, a lighter coloured head, and longer whiskers. Sea otters spend much time floating on their backs, which river otters never do. They rarely come ashore, unlikely river otters, and usually only on remote offshore reefs or bars.
Global 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.
Provincial Reproduction Comments: Females reach sexual maturity at three to five years (Bodkin et al. 1993); males between five and six years of age (Riedman and Estes 1990). Both sexes remain reproductive until death. Females average pup production is 0.90 pups per year (Siniff and Ralls 1991; Bodkin et al. 1993; Riedman et al. 1994). Mating occurs year-round with a peak in summer, followed by delayed implantation. Peak pupping in BC occurs in March and April (Watson 1993).
Global 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).
Provincial Ecology Comments: Sea otters are considered keystone species of nearshore ecosystems (Estes and Duggins 1995; Watson 1993; Kvitek and Oliver 1992). Their presence in nearshore marine ecosystems increases overall diversity and productivity (Gerber and VanBlaricom 1998), although prey species (eg sea urchins, sea cucumbers) suffer initial declines following colonization of an area by sea otters (Watson 1993). Loss of sea otters from the nearshore ecosystem also has impacts. Dramatic declines of sea otters throughout Alaska's Aleutian Islands caused a significant kelp deforestation and the vertebrate and invertebrate communities supported by kelp forests (Estes et al. 1998).
Migration Characteristics:
(Global / Provincial)		 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant: 		Y / Y
Y / N
N / N
na / N
Global Migration Comments: Seasonal movements occur among some age-sex classes in certain areas (Riedman and Estes 1990).
Provincial Mobility & Migration Comments: Sea otters establish indivisual home ranges. These incorporate feeding areas and resting areas which overlap with individuals of the same sex. Only males establish and defend territories that are established seasonally near female rafting areas (Reidman and Estes 1990). Females move freely through male territories. Male home ranges in California varied from 40.3ha TO 78 ha; female home ranges were generally smaller (Jameson 1989). Linear home range estimates of radiotagged male and female sea otters in Washington averaged 43 and 35 km, respectively, (Laidre 2004 in Lance et al. 2004). Males generally expand into new habitat first in response to increased population density at established sites (Kenyon 1969). Females follow into the new habitat once the male groups have moved on (Garshelis et al. 1984). Sea otters appear to make seasonal movements in response to sea conditions, moving to relatively sheltered locations during storms (Watson 1993). Male sea otters in particular, are capable of moving great distances. Males were reported to travel as much as 100 km over several days in Prince William Sound (Garshelis and Garshelis 1984) and 127 km in California ( Jameson 1989). One male moved 75 km in less than 23 hours (Jameson 1989). Occasional extralimital sightings are made off Haida Gwaii (N. Sloan pers. comm. 2005) and in other areas beyond their current range in BC.
Habitats:
(Type / Subtype / Dependence) 		Ocean / Eelgrass Beds / Facultative - occasional use
Ocean / Intertidal Marine / Facultative - frequent use
Ocean / Kelp Bed / Obligate
Ocean / Marine Island / Facultative - occasional use
Ocean / Sheltered Waters - Marine / Facultative - occasional use
Ocean / Subtidal Marine / Facultative - frequent use
Other Unique Habitats / Beach / Facultative - occasional use
Global 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.
Provincial Habitat Comments: Note on Habitats above: primarily use Near Shore Marine habitats consisting of continuously submerged, offshore waters. Sea otters are also found in Bay/Sound; Tidal flat/Shore; River mouth/Tidal river; and Lagoon habitats as defined here.
"In British Columbia, sea otters occur along stretches of exposed coastline characterized by complex rocky shorelines with small islets and offshore rocky reefs. Throughout their range in the North Pacific, sea otters occur in shallow coastal waters not generally deeper than 40 m and seldom range beyond 1-2 km of shore, although in areas where shallows extend well offshore they have been found well beyond 2 km (Riedman and Estes 1990)" (Sea Otter Recovery Team 2004). Kelp beds and soft-bottom communities provide important foraging habitats (Kvitek et al. 1993, 1992). Kelp beds are also used habitually as rafting sites. Most foraging occurs in subtidal zones and occasionally in intertidal areas at high tide (Estes 1980; VanBlaricom 1988). Forays onto land at low tide to feed on exposed mussels are rare (Harrold and Hardin 1986). Sea otters otherwise rarely go ashore. Anecdotal evidence from British Columbia suggests sea otters may aggregate in protected inshore areas during storms (Sea Otter Recovery Team 2004).
Food Habits: Invertivore: Adult, Immature
Piscivore: Adult, Immature
Global Food Habits 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).
Provincial Food Habits Comments: Sea otter diet is broad and diet varies geographically, often showing individual preferences. In habitats with rocky substrate, sea urchins are a preferred prey, but as urchins availability is reduced, diet shifts to a variety of marine invertebrates including bivalves, snails, chitons, crabs, sea stars and occasionally fish (Estes et al. 1981). Sea otters also forage in soft bottom habitat. Important components of sea otter diet include butter clams, horse clams and geoducks (Keple 2000; Kvitek et al. 1992).
Global Phenology: Circadian: Adult, Immature
Global Phenology Comments: Foraging occurs throughout the day and night, with periodic resting in between feeding bouts.
Provincial Phenology:
(1st half of month/
2nd half of month)		 Jan: Active / Active
Feb: Active / Active
Mar: Reproducing / Reproducing
Apr: Reproducing / Reproducing
May: Reproducing / Reproducing
June: Active / Active
July: Active / Active
Aug: Active / Active
Sept: Active / Active
Oct: Active / Active
Nov: Active / Active
Dec: Active /
Colonial Breeder: N
Length(cm)/width(cm)/Weight(g): 150/ / 35000
Elevation (m) (min / max): Global: 
Provincial: 
   
 
Distribution
Endemic: N
Global Range Comment: 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.
 
Authors / Contributors
Global Information Author: Hammerson, G.
Last Updated: May 02, 1995
Provincial Information Author: Ian Adams
Last Updated: Mar 17, 2005
   
References and Related Literature
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC.
Backhouse, F. 2000. Extinct and Extirpated Species. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 6pp.
Blood, D.A. 1993. Sea Otter. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 6pp.
Bodkin, J. L., D. Mulcahy, and C. J. Lensink. 1993. Age-specific reproduction in female sea otters (Enhydra lutris) from south-central Alaska: analysis of reproductive tracts. Can. J. Zool. 71:1811-1815.
Bodkin, J.L., D. Mulcahy, and C.J. Lensink. 1993. Age-specific reproduction in female sea otters (Enhydra lutris) from south-central Alaska: analysis of reproductive tracts. Can. J. Zool. 71:1811-1815.
Brody, A. J., K. Ralls, and D. B. Siniff. 1996. Potential impact of oil spills on California sea otters: implications of the Exxon Valdez spill in Alaska. Marine Mammal Science 12:38-53.
COSEWIC. 2007k. COSEWIC assessment and update status report on the sea otter Enhydra lutris in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 36pp.
DeGrange, A. R., and M. M. Vacca. 1989. Sea otter mortality at Kodiak Island, Alaska, during summer 1987. J. Mamm. 70:836-838.
Estes J.A. and D.O. Duggins. 1995. Sea otters and kelp forests in Alaska: generality and variation in a community ecological paradigm. Ecological Monographs. 65:75-100.
Estes, J. A. 1990a. Indices used to assess status of sea otter populations: a reply. J. Wildlife Management 54:270-272.
Estes, J. A. 1990b. Growth and equilibrium in sea otter populations. J. Animal Ecology 59:385-401.
Estes, J. A., D. O. Duggins, and G. B. Rathbun. 1989. The ecology of extinctions in kelp forest communities. Conservation Biology 3:252-264.
Estes, J.A. 1980. Enhydra lutris. Mammalian Species, 133:1- 8.
Estes, J.A. 1980. Enhydra lutris. Mammalian Species. 133:1-8.
Estes, J.A., et al. 1998. Killer whale predation on sea otters linking oceanic and nearshore ecosystems. Science 282:473-475.
Estes, J.A., R.J Jameson, and A.M. Johnson. 1981. Food selection and some foraging tactics of sea otters. Pp. 606-641 in J.A. Chapman, and D. Pursley, eds. Worldwide furbearers conference proceedings.
Garshelis D.L. and J.A. Garshelis. 1984. Movements and management of sea otters in Alaska. Journal of Wildlife Management. 48: 665-678.
Garshelis, D. L., et al. 1990. Indices used to assess status of sea otter populations: a comment. J. Wildlife Management 54:260-269.
Garshelis, D.L., A.M. Johnson and J.A. Garshelis. 1984. Social organization of sea otters in Prince William Sound, Alaska. Canadian Journal of Zoology. 62:637-647.
Gerber L.R. and G.R. VanBlaricom. 1998. Potential fishery conflicts involving sea otters (Enhydra lutris [L.]) in Washington State waters. Marine Mammal Commission. Washington, DC.
Jameson, R.J. 1989. Movements, home range, and territories of male sea otters off central California. Marine Mammal Sci. 5:159-172.
Jamieson, G.S., and J. Lessard. 2000. Marine protected areas and fisheries closures in British Columbia. Spec. Publ., Can. J. Fish. Aquat. Sci.:131. 414pp.
Jones, J. K., Jr., R. S. Hoffman, D. W. Rice, C. Jones, R. J. Baker, and M. D. Engstrom. 1992a. Revised checklist of North American mammals north of Mexico, 1991. Occasional Papers, The Museum, Texas Tech University, 146:1-23.
Kenyon, K. W. 1969. The sea otter in the eastern Pacific Ocean. North Am. Fauna 68:1-352.
Kenyon, K. W. 1982. Sea otter. Pages 704-710 in Chapman, J. A., and G. A. Feldhammer, editors. Wild mammals of NorthAmerica. Biology, management, and economics. Johns Hopkins Univ. Press, Baltimore.
Kenyon, K.W. 1969. The sea otter in the eastern Pacific Ocean. North Am. Fauna. 68:1-352.
Keple, A. 1999. Foraging behaviour and diet of the sea otter (Enhydra lutris) on soft-bottom sediments in Kyuquot, British Columbia. Unpubl. undergraduate thesis, Malaspina University-College. Nanaimo, BC.
Kvitek, R.G., C.E. Bowlby, and M. Staedler. 1993. Diet and foraging behaviour of sea otters in Southeast Alaska. Marine Mammal Sci. 9:168-181
Kvitek, R.G., et al. 1992. Changes in Alaskan soft-bottom prey communities along a gradient in sea otter predation. Ecology 73:413-428.
Loughlin, T.R. 1980. Home range and territoriality of sea otters near Monterey, California. J. Wildl. Manage. 44:576-582.
Matthews, J.R. and C.J. Moseley (eds.). 1990. The Official World Wildlife Fund Guide to Endangered Species of North America. Volume 1. Plants, Mammals. xxiii + pp 1-560 + 33 pp. appendix + 6 pp. glossary + 16 pp. index. Volume 2. Birds, Reptiles, Amphibians, Fishes, Mussels, Crustaceans, Snails, Insects, and Arachnids. xiii + pp. 561-1180. Beacham Publications, Inc., Washington, D.C.
Payne, S. F., and R. J. Jameson. 1984. Early behavioral development of the sea otter, Enhydra lutris. J. Mammalogy 65: 527-531.
Ralls, K., T. C. Eagle, and D. B. Siniff. 1996. Movement and spatial use patterns of California sea otters. Canadian Journal of Zoology 74:1841-1849.
Raloff, J. 1993. An otter tragedy. Science News 143:200-202.
Reeves, R. R., B. S. Stewart, and S. Leatherwood. 1992. The Sierra Club Handbook of Seals and Sirenians. Sierra Club Books, San Francisco, California. xvi + 359 pp.
Ribic, C.A. 1982. Autumn movement and home range of sea otters in California. J. Wildl. Manage. 46:795-801
Ridgway, S. H., and R. Harrison. 1981. Handbook of marine mammals. Vol. 1. The walrus, sea lions, fur seals and sea otter. Academic Press, New York. 235 pp.
Riedman, M. 1990a. The Pinnipeds: Seals, Sea Lions and Walruses. University of California Press, Berkeley, California. xxiii + 439 pp.
Riedman, M. 1990b. Sea otters. Monterey Bay Aquarium, Monterey, California. 80 pp.
Riedman, M. L., and J. A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology, and natural history. U.S. Fish and Wildlife Service Biological Report 90(14). 126 pp.
Riedman, M.L., et al. 1994. Breeding patterns and reproductive success of California sea otters. J. Wildl. Manage. 58:391-399.
Riedman, M.L., and J.A. Estes. 1990. The sea otter (Enhydra lutris): Behaviour, ecology and natural history. U.S. Fish and Wildl. Serv. Biol. Rep. 90(14). 126pp.
Sea Otter Recovery Team. 2004. National Recovery Strategy for the Sea Otter (Enhydra lutris) in Canada. Dep. Fish. and Oceans Can. Online. Available: http://www-comm.pac.dfo-mpo.gc.ca/pages/consultations/sea-otters/default_e.htm
Siniff, D. B., and K. Ralls, eds. 1988. Final report on contract 14-12-001-3003, Population status of California sea otters. U.S. Dept. of Interior, Minerals Management Service, Los Angeles, CA.
Siniff, D.B., and K. Ralls. 1991. Reproduction, survival and tag loss in California sea otters. Marine Mammal Sci. 7:211-229.
U.S. Fish and Wildlife Service (USFWS). 2000. Notice of designation of the Northern Sea Otter in the Aleutian Islands as a candidate species. Federal Register 65:67343-67345.
Van Blaricom, G.R. 1988. Effects of foraging by sea otters on mussel-dominated intertidal communities, Pp.48-91 in G.R. Van Blaricom and J.A. Estes, eds. The Community Ecology of Sea Otters. Springer Verlag. Berlin, Germany.
Watson, J.C. 1993. The effects of the sea otter (Enhydra lutris) foraging on shallow rocky communities off northwestern Vancouver Island, British Columbia. Ph.D. dissertation. Univ. of California, Santa Cruz, CA.
Watson, J.C., G.M. Ellis, T.G. Smith, and J.K.B. Ford. 1997. Updated status of the sea otter, Enhydra lutris, in Canada. Can. Field-Nat. 111:277-286.
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/.
Wilson, D.E., et al. 1991. Geographic variation in sea otters Enhydra lutris. J. Mammal. 72:22-36
Wilson, D.E., M.A. Bogan, R.L. Brownell, Jr., A.M. Burdin, and M.K. Maminov. 1991c. Geographic variation in sea otters, Enhydra lutris. Journal of Mammalogy 72:22-36.
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 1995. Species Summary: Enhydra lutris. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 7, 2026).