Northern sea otters are a
subspecies of sea otter found in the Aleutian Islands and
the coasts of south mainland Alaska, British Columbia,
and the U.S. State of Washington. This fact sheet will
focus only on information related to this subspecies. For
general sea otter information, refer to the Sea Otter (Enhydra
Lutris) fact sheet.
Northern sea otters share the basic
physical characteristics of all Enhydra lutris sea otters,
though they are said to be intermediate in size when compared
to the larger Asian sea otter (Enhydra lutris lutris) and
the smaller Southern sea otter (Enhydra lutris nereis).
They are also said to have longer mandible bones than the
other two subspecies. Northern sea otters are more likely
to haul out on land and are more agile on land than both
Southern sea otters and Asian sea otters (Davis, Lidicker,
1975).
After sea otters were nearly killed off by the fur
trade in the 1700-1800s, they were finally protected by
international treaty in 1911. Protection permitted populations
to grow at a rate of 9% annually, and in some areas of the
Aleutians, numbers approached pre-exploitation levels. By
the 1980s, northern sea otters had reached all major Alaskan
islands that they formerly inhabited.
Recovery of the Kenyoni
subspecies was further aided by translocation efforts in
the late 1960s. Northern sea otters from Amchitka and Prince
William Sound were released in Oregon, Washington, and
British Columbia, and stable populations were established
everywhere except Oregon. Failure to recover in Oregon
is assumed to be a result of an inadequate food supply.
Populations in Washington are increasing at a rate of 8.2%
per year and are on track to reach capacity (Jameson, 2005).
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| Picture
of northern sea otter or Alaskan
sea otter, Enhydra
lutris kenyoni, mother and
pup, Prince William Sound, Alaska,
North Pacific Ocean |
Image
#: 010954 |
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Kingdom:
Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Carnivora
Suborder: Caniformia/Canoidea
Family: Mustelidae/Mustelids
Genus: Enhydra
Specific: lutris
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Thanks
to natural recovery and translocation efforts, northern
sea otters were expected to increase further in population
throughout their historical range. Unfortunately, surveys
in the 1990s discovered an unexpected and abrupt decline
in Northern sea otter numbers in the Aleutian Islands.
A survey in 2000 showed that Northern sea otters had declined
by 70% from 1992 to 2000. In terms of number, that represents
a catastrophic loss of 47,000 to 86,000 northern sea otters
in the Aleutian Islands alone (Burn, Doroff, Tinker, 2003).
Year 2000 population estimates in the Aleutians were less
than 9,000 individuals remaining (Doroff, Estes, Tinker,
Burn, Evans, 2003).
The reasons for this sudden drop-off
in numbers in the Aleutian Islands are not entirely known.
One reason put forth was increased predation by orcas (killer
whales), which was probably due to an abrupt decline in
numbers of the orca's preferred prey, harbor seals (Doroff,
Estes, Tinker, Burn, Evans, 2003). The sudden drop in both
pinnipeds and northern sea otters is a cause for concern,
and provides evidence that sea otter populations must be
protected and monitored wherever they occur.
Sea otters
are listed as Threatened in Canada. Northern sea otters
occupy small areas of the British Columbia coast and are
said to be increasing in number there, with recent estimates
at around 900 sea otters from an initial translocation
of 89 individuals from Alaska in 1969 and 1972. Oil spills,
environmental contamination, disease or fishing conflicts
could adversely impact any of these populations, so they
are by no means secure.
Sea otters in the State of Washington
are listed as Endangered, though this designation will
likely be downgraded to Threatened when sea otters reach
a count of 1,640 individuals or more for 3 consecutive
years. The most recent counts have been about half that.
This number may seem small, but they are the offspring
of only 59 sea otters that were reintroduced to Washington
in 1969 and 1970. Like the British Columbia populations,
they could be severely impacted by oil spills or other
environmental disasters.
The number of sea otters in Alaska
may be as high as 150,000. They continue to decrease in
the Aleutians, but are increasing along the south mainland
coast and the panhandle bordering British Columbia. The
Aleutian population, called the Southwest Alaska stock of
sea otters, is considered Threatened. The other stocks,
called the South Central Stock and the Southeast Stock,
are considered stable and are not designated as Threatened.
All
sea otters now in existence are descendants of a fairly
small number of exploitation era survivors. Consequently,
there is little genetic diversity among sea otter populations,
making them particularly vulnerable to disease or sudden
environmental change.
Alternate names: Northern Sea Otter,
Alaskan Sea Otter, Alaska Sea Otter
Links to SeaPics.com
fact sheets on the other two subspecies of sea otter:
Asian
sea otter (Enhydra lutris lutris) of Japan and Russia
Southern
sea otter (Enhydra lutris nereis) of California
© Northern
sea otter information assembled from on-line sources by
Kevin
Miller on June 4, 2008 for Seapics.com.
http://www-comm.pac.dfo-mpo.gc.ca/pages/consultations/sea-otters/recovery_e.htm
http://research.alaskasealife.org/otter_articles/Doroff_etal2003-Sea_Otter_Population_Declines_In_the_Aleutian_Archipelago.pdf
http://research.alaskasealife.org/otter_articles/Bodkin_etal2003-Sea_otter_pop_structure.pdf
http://research.alaskasealife.org/otter_articles/Davis_etal1975-Taxonomic_status.pdf
http://wdfw.wa.gov/wlm/research/papers/seaotter/survey/index.htm
http://wdfw.wa.gov/wlm/diversty/soc/recovery/seaotter/index.htm
http://www.adfg.state.ak.us/special/esa/non-endangered.php |
