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BC Conservation Data Centre: Conservation Status Report

Enhydra lutris
Sea Otter

 
Scientific Name: Enhydra lutris
English Name: Sea Otter
   
Provincial Status Summary
Status: S3S4
Date Status Assigned: January 05, 2022
Date Last Reviewed: January 05, 2022
Reasons: Abundance and range have both increased substantially since reintroductions occurred; however, there are only 2 main populations and they face numerous threats.
 
Range
Range Extent: E = 5,000-20,000 square km
Range Extent Comments: From 1969-72, 89 sea otters were reintroduced to Checleset Bay on the northwest coast of Vancouver Island. By 2004, the population expanded its range south to Vargas Island in Clayoquot Sound and north to Cape Scott and eastward to Hope Island in Queen Charlotte Strait. Off the central coast of British Columbia, sea otters range from the Goose Islands Group to the edge of Milbanke Sound (Convey and Nichol unpubl. data). Extralimital sightings of individual animals outside this range are reported, including Haida Gwaii (N. Sloan pers. comm.). Sea otters also occur across the Strait of Juan de Fuca in Washington State, between Destruction Island and Pillar Point (Lance et al. 2004). In 1996 a sea otter was observed in the San Juan Islands but there has been no known migration between the Washington and B.C. populations (Lance et al. 2004). A rough estimate of 15,000 km2 can be made for sea otters in B.C.
Area of Occupancy (km2): HI = 2,501 to >12,500
Area of Occupancy Comments: This range is defined as the continuously occupied range, or the range in which groups of sea otters have been observed during surveys made in late spring and summer (Convey and Nichol unpubl. data). Therefore, Area of Occupancy is roughly equal to the Extent of Occurrence.
 
Occurrences & Population
Number of Occurrences: A = 1 - 5
Comments: Based on NatureServe's (2005) separation criteria for sea otter "occurrences" (50 km both suitable and unsuitable habitat), there are two occurrences of sea otter in British Columbia. The Vancouver Island area or sub-population (genetically, they are considered one population) may be considered one occurrence. Although there may be 50 km stretches of coastline without otters at any given time along their Vancouver Island range, seasonal movements within and beyond their distribution (see Sea Otter Recovery Team 2004) indicate that they be considered contiguous.
Number of Occurrences with Good Viability / Ecological Integrity: B = 1 - 3
Comments: Both Vancouver Island and central mainland coast occurrences are growing and appear viable. However, the effects of threats - particularly a catastrophic oil spill - cannot be estimated.
Number of Occurrences Appropriately Protected & Managed: B = 1 - 3
Comments: Sea otters have been protected coast-wide from killing since the International Fur Seal Treaty (1911), although illegal killings have been reported. Habitat occupied by sea otters is protected in various locations on Vancouver Island to differing levels of protection degrees (Jamieson and Lessard 2000). An Ecological Reserve at the reintroduction site in Checleset Bay was established in 1981 (Watson et al. 1997) specifically to protect sea otters and their habitat. Hakai Pass is the only protected area within their current range on the Central Coast (Jamieson and Lessard 2000).
Population Size: E = 2,500 - 10,000 individuals
Comments: The number of mature adults is estimated at 1600. The highest counts in 2001 provide a minimum population size estimate of 2673 individuals off Vancouver Island and a further 507 off the Central BC Coast (COSEWIC 2007). Sea otter surveys are designed to provide an index of population size.
 
Threats (to population, occurrences, or area affected)
Degree of Threat: AC = Very high - medium
Comments: Threats include oil spills, disease and parasites, genetic diversity, contaminants, entanglement in fishing gear, collisions with vessels and illegal kill and human disturbance. Oil spills remain the most significant threat to sea otters in British Columbia because of the population's size and distribution and the species' inherent vulnerability to oil. The probability or proportion of a population that would survive an oil spill is unknown (Sea Otter Recovery Team 2004), but the potential for it to have "high" scope and severity is very real. Bonnell et al. (1996) concluded that even relatively small oil spills "can cause a major and perhaps irrecoverable impact on the [a] sea otter population". Disease and parasites are a significant concern in California (Thomas and Cole 1996; Estes et al. 2003). Interactions with human activities, including entanglements / entrapments, collisions and illegal killing may become a greater concern in the future as sea otters move into more densely human-populated areas.
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: I = Increase of >25%
Comments: Between 1977 and 1995, the population increased at an estimated mean rate of 18.6% per year (Watson et al. 1997), near the sea otter's theoretical maximum rate of increase (Estes 1990). Overall, annual growth continues to be positive, with a rate of 8% per year between 1995 and 2004. The rate of increase for the population on the central coast has been estimated at 12.4% per year between 1990 and 2004 (COSEWIC 2007).
Long-Term Trend: AC = Decline of >70%
Comments: The pre-extirpation numbers are unknown, other than "numerous". Between 1785 and 1809 over 55,000 pelts were brought into BC. The origin of all of the pelts are difficult to determine but it is known that at least 6000 were from the west coast of BC (in COSEWIC 2007).

The population was re-introduced between 1969 and 1972.
 
Other Factors
Intrinsic Vulnerability: B=Moderately vulnerable
Comments: Sea otters have a relatively late age of maturity and low reproductive rate. However, given suitable habitat conditions, populations are capable of steady, long-term (20 - 30 years) growth and in newly occupied habitat where prey are not limiting, high annual growth rates are possible. Populations remain at (potentially significant) risk from identified threats.
Environmental Specificity: C=Moderate. Generalist or community with some key requirements scarce.
Comments: Sea otters have fairly general habitat and food requirements. They occur in a moderate range of habitat types and consume a variety of foods. However, they are highly vulnerable to environmental contamination, particularly oil spills.
Other Rank Considerations:
 
Information Gaps
Research Needs: Knowledge gaps are outlined by the Sea Otter Recovery Team (2004):1. Oil spill risk modelling and impacts of oil and gas exploration. 2. Genetic diversity within and between populations and compared to source population. 3. Health monitoring (disease and parasites, contaminants) and identifying other sources of mortality. 4. Critical habitat identification (rafting and foraging areas, seasonal variations, and movements and home range patterns). 5. Assess entanglements and entrapments in fishing gear and interactions with aquaculture gear. 6. Interactions between sea otters and aquaculture.
Inventory Needs: 1. Regular surveys using the standardized procedure are required to maintain a survey time series with which to estimate the index population size. 2. Document distribution.
 
Stewardship
Protection: 1. Maintain fur-harvest ban. 2. In critical habitat (once defined), prohibit activities that may result in its destruction.
Management: 1. Develop an oil spill response plan for sea otters and prepare to implement the plan in the event of an oil spill. 2. New oil spill regulations to reduce risk of spills and risk of spills contacting sea otters. 3. Minimize disturbance (e.g. from vessel traffic or marine mammal viewing) to important areas or habitats . 4. Develop viewing guidelines specific for sea otters. 5. Work with Aquaculture industry to minimize damage to both sea otters and aquaculture operations.
 
Version
Author: Ian Adams, Linda Nichol and L. Ramsay
Date: May 26, 2010
 
References
Blood, D.A. 1993. Sea Otter. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 6pp.
Bonnell, M.L., R.G. Ford, and A.J. Brody. 1996. Assessing the threat of oil spills to southern sea otters. Endangered Species Update 13(12):38-42.
Breen, P.A., T.A. Carson, J.B. Foster, and E.A. Stewart. 1982. Changes in subtidal community structure associated with British Columbia Sea Otter transplants. Mar. Ecol. Prog. Ser. 7:13-20.
Convey, L. and L. Nichol. 2005. Unpublished data. Fisheries and Oceans Canada. Nanaimo, BC.
COSEWIC. 2022. Sea Otter (Enhydra lutris): COSEWIC assessment and status report 2022
Estes, J.A. 1990. Growth and equilibrium in sea otter populations. J. Animal Ecol. 59:385-401.
Estes, J.A., et al. 2003. Causes of mortality in California sea otters during periods of population growth and decline. Marine Mammal Sci. 19:198-216.
Gregr, E., L. Nichol, J.C. Watson et al. 2008. Estimating carrying capacity for Sea Otters in British Columbia. Journal of Wildlife Management 72: 382-388.
Harrold, C., and D. Hardin 1986. Prey consumption on land by the California sea otter, Enhyrda lutris. Marine Mammal Sci. 2:309-313.
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.
Lance, M.M., S.A. Richardson, and H.L. Allen. 2004. Washington state recovery plan for the sea otter. Washington Department of Fish and Wildlife, Olympia.
MacAskie, I. 1987. Updated Status of the Sea Otter, Enhydra lutris, in Canada. Can. Field-Nat. 101(2):279-283.
Nagorsen, D. 1990. The mammals of British Columbia: a taxonomic catalogue. Mem. No. 4. Royal B.C. Mus., Victoria. 140pp.
Nagorsen, D.W. 1998. Checklist of the mammals of British Columbia, Royal B.C. Mus. Online. Available: http://www.royalbcmuseum.bc.ca/nh_papers/mammals/index.html
NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life [web application]. Version 4.2. NatureServe, Arlington, VA. Available: http://www.natureserve.org/explorer [Accessed: January 13, 2005].
Nichol, L.M., Doniol-Valcroze, T., Watson J.C, et al. 2020. Trends in growth of the sea otter (Enhydra lutris) population in British Columbia 1977 to 2017. DFO Can. Sci. Advis. Sec. Res. Doc. 2020/039. vii + 29 p.
Richardson, S., and H. Allen. 2000. Draft Washington state recovery plan for the sea otter. Washington Dep. Fish and Wildl., Olympia, WA.
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
Thomas, N.J., and R.A. Cole. 1996. The risk of disease and threats to the wild population. Endangered Species Update 13(12):23-27.
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., et al. 1991. Geographic variation in sea otters Enhydra lutris. J. Mammal. 72:22-36
 

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.

Suggested Citation:

B.C. Conservation Data Centre. 2010. Conservation Status Report: Enhydra lutris. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Nov 26, 2024).