Northern Sea Otter -Kara Vane

The Northern Sea Otter of Southwest Alaska

Kara Vane

Northern Sea Otter Description and Ecology

Sea otters, Enhydra lutris, are the largest mustelid, and ironically the smallest marine mammal as well. This species is most widely known for its dense pelage. The coat contains 100,000-400,000 hairs per square centimeter; put into perspective, humans have merely 20,000 hairs covering their head.[1] Check out this link for more information. Sea otters are a very social species and group together by gender. They are generalist predators who consume more than 150 prey species. In fact, they will eat most any seafood that they can find in their habitats and generally eat about 25% of their body weight. This large consumption of food is a result of their high metabolic rates.[2] Otters dive to the see floor to forage for food and once these creatures capture their prey, they crush it rather than shear it. Sea otters are an example of a keystone species and their decline has resulted in ecosystem changes. More specifically, they affect their ecosystem in that they protect kelp forests from overgrazing by sea urchins. When abundant, otters eat large amounts of sea urchins, who consume kelp. But, when there are low levels of sea otters, the sea urchins becomes overabundant and can prevent kelp forests from establishing. This is known as a “trophic cascade.” The Northern sea otter is one of three subspecies and I will be specifically focusing on the subspecies population located in southwest Alaska.

Geographic and Populations Changes

The Northern Sea Otter occurs in the North Pacific Ocean between California and Japan in mainly coastal marine habitats. They are physiologically limited to shallow waters due to their diving methods of capturing prey. Sea otters are the only marine mammal species without blubber and as a result, rely on their dense coat of fur to insulate them from the cold waters. This reliance on their fur for insulation unfortunately makes them very vulnerable to oil spills. [3] Furthermore, the Russian Bering Expedition in 1741 led to the discovery of this dense fur as well. After realizing the value of these creatures’ pelage, the commercial fur harvest for their coats exploded, lasted 170 years and eventually led to the sea otter’s decline and extirpation from many areas. This page gives a more detailed look at the history of the otter fur trade. Sadly, by the end of that time there were fewer than 1,000 individuals left in 13 remaining colonies.[4] These sea otter populations grew and re-colonized over time during the 20^th century. However, there were some exceptions to this growth including the Aleutian archipelago population, which shifted from expansion to decline. Currently, the population is dangerously low in much of the Aleutian Islands. 

Listing Date and Type of Listing

Studies indicate that the southwest Alaska population of northern sea otters had declined in abundance by more than 50% since the mid 1980’s. In 2005, the US Fish and Wildlife Service listed this particular population of Northern Sea Otters as threatened.

Cause of listing and Main threats to its continued existence

The Northern Sea Otter population fell by 70% between 1992 and 2000 and another 63% between 2000 and 2003. Predation by the killer whale is the main cause of overall decline in this species. Take a look at this video of whale vs. otter. Other threats to the sea otters' continued existence include infectious disease, bio-toxins, contaminants, oils spills, food limitation, disturbance, bycatch in fisheries, subsistence harvest, loss of habitat and illegal take.[5]

Description of Recovery Plan

The otters occur in many different habitat types, and the recovery plan identifies 5 management units (MU’s) within the population segment to address the differences. The recovery plan addresses each threat generally and then assesses their importance, by ranking them, relative to each of the five MU’s.

The goal of the recovery program is to control or reduce threats to the southwest Alaska northern sea otter so that it can be delisted. According to the FWS Recovery Plan, to achieve this goal, three objectives are identified: “achieve and maintain a self-sustaining population of sea otters in each MU, maintain enough sea otters to ensure that they are playing a functional role in their near shore ecosystem, and mitigate threats sufficiently to ensure persistence of sea otters” (FWS Recovery Plan). Research and management action costs for this recovery plan total 2.665 million to 3.650 million over the first 5 years- greatest challenges will be to secure funding.[6]

See for yourself how cute sea otters are! Click here

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[1] http://marinebio.org/species.asp?id=157

[2] http://www.fws.gov/alaska/fisheries/endangered/pdf/Nseaotter_factsheet_v2.pdf

[3]  http://ecos.fws.gov/docs/recovery_plan/Recovery%20Plan%20SW%20AK%20DPS%20Sea%20Otter%20Aug13.pdf

[4] http://marinebio.org/species.asp?id=157

[5] http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A0HK#recovery

[6] http://ecos.fws.gov/docs/recovery_plan/Recovery%20Plan%20SW%20AK%20DPS%20Sea%20Otter%20Aug13.pdf

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