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Sea otter (Enhydra lutris) COSEWIC assessment and status report 2007L chapter 13

Technical Summary

Enhydra lutris

Sea otter
Loutre de mer

Range of Occurrence in Canada: Pacific Ocean


Extent and Area Information

Extent of occurrence (EO) (km 2 )
Coastal waters of west coast Vancouver Island and central British Columbia coast where sea otter occupation has been confirmed from dedicated surveys and from ATK . It does not include sightings of single animals outside this continuously occupied range. Area is calculated from shore to the 50 m depth contour; deep inlets are cut off.
10 000 km 2
Specify trend in EO
Increasing
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km 2 )
same as EO
10 000 km 2
Specify trend in AO
Increasing
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations
2
Specify trend in #
None
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
Increasing


Population Information

Generation time (average age of parents in the population)
age at first birth = 3, longevity = 15 to 20, gen.time = 3 + .33(15-3) to 3 + .33(20-3)
7 to 9 years
Number of mature individuals
Data to produce a life table do not exist for British Columbia. The proportion of adults is assumed to be 50% of the total population based on estimates of age at first reproduction of other sea otter populations.
~ 1 600 adults
Total population trend
Population data from Watson et al. 1997 and Nichol et al. 2005 indicate that the population has been increasing.
Vancouver Island
18.6% yr -1 (1977-1995)
15.6% yr -1 (1977-2004)
19.1% yr -1 (1977-1995)
8.0% yr -1 (1995-2004)

Central B.C. coast
12.4% yr -1 (1990-2004)
% decline over the last/next 10 years or 3 generations
None over last 10 years
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
No
Specify trend in number of populations
N/A
Are there extreme fluctuations in number of populations?
Not in Canada
Populations with number of mature individuals in each:
A crude estimate based on 50% of the population being reproductive might be 1350 on Vancouver Island and 250 on the central coast


Threats (actual or imminent threats to populations or habitats)

Environmental contamination, especially oil spills, entanglement in fishing gear and collision with vessels, illegal killing.

 


Rescue Effect (immigration from an outside source)

Status of outside population(s)
U.S. federal Endangered Species Act: California – Threatened,  Southwestern Alaska Stock – Threatened,
State Special Species Policy – Washington – Endangered
Is immigration known or possible?
Yes, wandering males
Would immigrants be adapted to survive in Canada?
Yes
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
Rescue is unlikely because sea otters are non-migratory, exhibit high site fidelity and occupy relatively small overlapping home ranges


Quantitative Analysis

[provide details on calculation, source(s) of data, models, etc]

None available

 


Current Status

COSEWIC: Threatened (2000)
Special Concern (2007)

 


Status and Reasons for Designation

Status: Special Concern
Alpha-numeric code: Not applicable

Reasons 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 (< 3500) and require careful monitoring. Their susceptibility to oil and the proximity to major oil tanker routes make them particularly vulnerable to oil spills.

 


Applicability of Criteria

Criterion A (Declining Total Population):
The population has increased at rates of 8 – 19% per year since censuses were initiated in 1977. The rate of increase has slowed in recent years.

Criterion B (Small Distribution, and Decline or Fluctuation):
Extent of occurrence is < 20 000 km2, but the population is not declining or fluctuating.

Criterion C (Small Total Population Size and Decline):
Total population is ~3200 animals of which half are assumed to be mature individuals (~1600). The population is small, but there is no decline or fluctuation in numbers.

Criterion D (Very Small Population or Restricted Distribution):
There are > 1000 mature individuals.

Criterion E (Quantitative Analysis):
None have been undertaken.

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