Enhydra lutris

The Sea Otter is the largest member of family Mustelidae, and the smallest marine mammal. Sea Otters are more aquatic even than seals and sea lions, because they mate and give birth in the water. They are tool users, using rocks to pound open hard-shelled prey, such as abalone. Once hunted almost to extinction for their fur, but now protected, they have made a comeback. This has stirred controversy where their predation on abalone, crabs, clams, and sea urchins affects shellfisheries. Ecologists are beginning to understand the larger, long-term role they play in shaping the marine environment, by eating creatures such as sea urchins. Sea urchins feed on and if unchecked, can destroy kelp. Vast underwater kelp forests are at the base of the coastal food web and also provide shelter for countless organisms.

Adaptation: In the sea otter (Enhydra lutris), adaptations to crushing marine invertebrates mark the skull through its powerful chewing muscles, which leave muscles scars in the form of raised ridges of bone and a rough surface texture. Note also the large, flat cheek teeth.

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Highly aquatic, the sea otter rarely comes ashore, both resting and feeding in coastal waters. Alaskan sea otters are more at home out of the water than their Californian relatives, often hauling out on sandbars and ice (8). Otters have a high metabolic rate (9) and these resourceful, opportunistic predators need to consume 25 percent of their body weight a day (6). Diving to depths of up to 75 metres they retrieve invertebrates such as mussels, snails, crabs and urchins from the seabed (6). Pouches of skin at the armpit of each forelimb can be used to store food whilst it is carried to the surface (6). Otters float on their backs, using their chest as a table whilst they attempt to prize open the shells. Sometimes rocks are used to smash open the hard shells and sea otters are one of the only mammals (apart from primates) to have developed tool use (6). Sea otters are considered a 'keystone species' in some parts of their range, as they appear to be vital in the maintenance of kelp forest ecosystems by suppressing the number of sea urchins that would otherwise overgraze the forests (4). These gregarious creatures can be found in large same-sex groups known as 'rafts'. Rafts in California rarely exceed 50 individuals but in Alaska, where the population density is higher, up to 2,000 otters can gather (2). Sea otters probably spend more time and energy grooming their fur that any other mammal; an important activity required to maintain the insulation of their fur, as it cleans and replenishes air to the under fur (4). Grooming involves rubbing, rolling and blowing air into the fur (4). Trapped air in the under fur is heated by the body to provide insulation and gives otters a silvery appearance underwater (5). Sea otters are polygynous, with adult males generally defending territories that encompass the ranges of several females (2) (4). While mating, the male will grip the female's nose with his teeth and she is often left with a bloody souvenir of their encounter (4). Females usually give birth to a single pup and carry them on their chest, nursing them and grooming them meticulously to ensure the fur remains buoyant and insulated (9). Young pups are left on the surface whilst their mother dives for food, but as they mature they follow her, learning to forage by watching her technique (5). Pups will stay with their mother for around three to six moths (6).

The sea otter, the smallest marine mammal in the world, is well adapted for its predominately aquatic lifestyle, possessing a strong, rudder-like tail and large hind-feet that act as flippers (2). Unlike other marine mammals, sea otters do not have blubber and instead rely on their fur to keep warm in the water (4); their reddish-brown coat is the densest of any mammal, consisting of around 100,000 hairs per cm² (2). The natural oils produced by the fur provide a waterproof quality (5).

Historically, Sea Otters occurred across the North Pacific Rim, ranging from Hokkaido, Japan, through the Kuril Islands, the Kamchatka Peninsula, the Commander Islands, the Aleutian Islands, peninsular and south coastal Alaska and south to Baja California, Mexico (Kenyon 1969). In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). Although it appears that harvests periodically led to local reductions of Sea Otters (Simenstad et al. 1978), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969). Remnant populations were located in the Kuril Islands, Kamchatka and in the Commander Islands Russia; five in Southwestern Alaska (the Aleutian Islands, Alaska Peninsula, and Kodiak Island), and one remnant population in each of the following regions; Southcentral Alaska (Prince William Sound), Canada (Queen Charlotte Islands), central California, and Mexico (San Benito Islands) (Estes 1980). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations have presumably died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

In north America, the Sea Ottes range is fairly continuous from the Aleutian Islands to Prince William Sound with population gaps along the Gulf of Alaska until Yakutat (which was a translocated population) with another gap in the population’s distribution until the outer islands of Southeast Alaska (also a translocated population form the Aleutian Islands and Prince William Sound). The next gap in the Sea Otter population distribution is between Southeast Alaska and British Columbia, Canada. Translocation efforts were successful in Washington State but not in Oregon thus there is a large population gap between the small Sea Otter population in Washington and that of central California.

Past distribution of the sea otter included Hokkaido Island of Japan north through the Kuril Islands and eastern coast of Kamchatka, east through the Commander Islands and Aleutian archipelago, the southern coast of Alaska, and the west coast of North America to Baja, Mexico. Sea ice limits their northern range to below 57 degrees N lattitude, and the distribution of kelp forests limits the southern range to about 22 degrees N lattitude. Hunting during the 18th and 19th centuries greatly reduced the distribution fo the sea otter. Three subspecies of Enhydra lutris are recognized today. E.l. lutris ranges from the Kuril Islands north to the commander islands in the western pacific. E.l. nereis is found off the coast of central California. E.l. kenyoni is distributed throughout the Aleutian Islands and southern Alaska, and has been reintroduced to various locations from south of Prince William Sound, Alaska to Oregon.

(Wilson et.al. 1991; Estes 1980; Nowak 1999)

Biogeographic Regions: pacific ocean (Native )

Alaska, Aleutian Islands, California, Commander Islands, Kamchatka, Kurile Islands, North Pacific

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) 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.

Historically, the sea otter was found in coastal areas throughout the North Pacific (6). Sea otters can still be found in much of this former range although numbers are greatly reduced and populations fragmented (6). Three subspecies are currently recognised: the southern, or California sea otter (Enhydra lutris nereis), occurs from California to Mexico; the northern, or Alaskan sea otter (E. l. kenyoni), is found along the northwest coast of North America and into Alaska; and the Russian sea otter (E. l. lutris) occurs in the western north Pacific (7). Alaska plays host to possibly as much as 90 percent of the world population of this species (6).

Sea otters are the largest member of the family Mustelidae. Males weigh 22 to 45 kg and are 1.2 to 1.5 m in length. Females are slightly smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length. The tail comprises less than a third of the body length. The pelage is brown or reddish brown. Sea otter fur is the densest of all mammals, with about 100,000 hairs per square centimeter. Since sea otters do not have any insulating fat, the fur is responsible for maintaining warmth. The hind legs are long and the paws are broad, flat, and webbed. The forelimbs are short and have retractable claws. Sea otters are the only carnivorans with just 4 lower incisors. Females have two mammae.

(Estes 1980; Nowak 1999)

Range mass: 14 to 45 kg.

Range length: 1 to 1.5 m.

Other Physical Features: endothermic ; bilateral symmetry

Average basal metabolic rate: 98.479 W.

Length: 150 cm

Weight: 35000 grams

Length:
Range: 1,260-1,450 mm males; 1,070-1,400 mm females

Weight:
Range: 18-45 kg males; 11-33 kg females

Differs from pinnipeds in longer tail and much smaller forelimbs that are not flipperlike. Differs from the river otter in shorter tail and flipperlike hind feet. This is the only carnivore with 2 pairs of lower incisors (all others have 3 pairs).

Habitat and Ecology

Systems

• Terrestrial
• Marine

Sea otters are marine mammals. They inhabit temperate coastal waters with rocky or soft sediment ocean bottoms less than 1 km from shore. Kelp forest ecosystems are characteristic of otter habitats.

(Estes 1980; Nowak 1999)

Average elevation: 0 m.

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: coastal

Other Habitat Features: intertidal or littoral

shallow, nearshore waters

Depth range based on 2071 specimens in 2 taxa.
Water temperature and chemistry ranges based on 78 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 3.977 - 13.353
  Nitrate (umol/L): 3.951 - 6.975
  Salinity (PPS): 31.536 - 33.310
  Oxygen (ml/l): 6.095 - 7.514
  Phosphate (umol/l): 0.674 - 1.024
  Silicate (umol/l): 5.723 - 20.291

Graphical representation

Temperature range (°C): 3.977 - 13.353

Nitrate (umol/L): 3.951 - 6.975

Salinity (PPS): 31.536 - 33.310

Oxygen (ml/l): 6.095 - 7.514

Phosphate (umol/l): 0.674 - 1.024

Silicate (umol/l): 5.723 - 20.291
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Habitat Type: Marine

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.

Sea otters inhabit near-shore rocky or soft-bottom coastal waters, and in California are particularly associated with dense kelp forests (4).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Seasonal movements occur among some age-sex classes in certain areas (Riedman and Estes 1990).

Sea otters are carnivorous. They will eat nearly any seafood they can find in their kelp forest foraging grounds. Their diet consists of marine invertebrate herbivores and filter feeders such as mussels, sea urchins (Strongylocentrotus sp.), snails, and abalone. Otters also are known to eat crabs, octopus, squid, sea stars, and fish. Individuals tend to be specialized in their choice of prey: one otter may consume only urchins and crabs while another will eat mostly fish, all depending on the abilities of the individual otter and what is available in the area. Otters need to consume 20-25% of their body weight each day. They obtain most of their water from prey but will drink seawater to satisfy thirst also.

(Limbaugh 1961; Estes 1980; Estes et.al. 1986; Cohn 1998; Nowak 1999)

Animal Foods: fish; mollusks; aquatic crustaceans; echinoderms; other marine invertebrates

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

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).

Sea otters are a keystone species. They play a major role in the community by controling of herbivorous invertebrates, mainly the sea urchin (Strongylocentrotus sp.), inhabiting kelp forests. Sea urchins graze on kelp. In coastal areas where otters are absent, sea urchins are abundant and the area is devoid of kelp forests. Where sea otters are present, the urchins are limited by otter predation and kelp forests are abundant. Kelp forests are dependent on sea otters for protection from grazers. The diversity of the sea otter diet reduces competition between benthic grazers and supports greater diversity in those species. The presence of sea otters is believed to be important in the evolution of kelp forest ecosystems.

(Estes and Palmisano 1974; Estes et.al. 1978; Estes 1980; Cohn 1998; Estes and Duggins 1995)

Ecosystem Impact: keystone species

Predation by killer whales is thought to be responsible for recent population declines. Vigilance and avoidance protects otters from predators other than humans.

(Limbaugh 1961; Estes 1980; McShane et.al. 1995; Estes 1998)

Known Predators:

• great white sharks (Carcharodon carcharias)
• killer whales (Orcinus orca)
• California sea lions (Zalophus californianus)
• bald eagles (Haliaeetus leucocephalus)
• humans (Homo sapiens)

Enhydra lutris is prey of:
Homo sapiens
Carcharodon carcharias
Haliaeetus leucocephalus
Orcinus orca
Zalophus californianus

Based on studies in:
USA: Alaska, Aleutian Islands (Coastal)

This list may not be complete but is based on published studies.

Enhydra lutris preys on:
Echinoidea
Decapoda
Actinopterygii
Tivela stultorum
Polinices
non-insect arthropods
marine invertebrates
Mollusca
Echinodermata
Crustacea
Castor canadensis

Based on studies in:
USA: Alaska, Aleutian Islands (Coastal)
USA: California (Coastal)

This list may not be complete but is based on published studies.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

10,000 to >1,000,000 individuals

Comments: Estimates from the mid- to late 1980s suggested populations of 6000-7000 in the Kuril Islands, 2000-2500 in the Commander Islands, and 2500-3000 off Kamchatka, giving a total western Pacific population of 10,500-12,500 (Riedman and Estes 1990, Reeves et al. 1992). In the 1980s, the total population from Prince William Sound to the Kuril Islands was about 150,000 (Riedman 1990). For the Aleutian Islands, the minimal population estimate was 8,742 sea otters in 2000 (Doroff et al. 2003).

Alaska had 100,000-150,000 in the mid- to late 1980s (Reeves et al. 1992), and the current population probably also is in this range (USFWS 1995 stock assessment). Prince William Sound population in late 1980s was about 14,000, of which an estimated 2800 were killed as a result of the Exxon Valdez oil spill (Raloff 1993). From an original 402 individuals translocated in the 1960s, the population in southeastern Alaska increased to more than 3500 in five populations by 1987 (Reeves et al. 1992); 1988 estimate was 4520 (See Riedman and Estes 1990).

In 1984, the population off west coast of Vancouver Island, British Columbia, was 345 (descended from 89 that were translocated from Alaska, 1969-1972) (MacAskie 1986); 1987 count was 380 (see Riedman and Estes 1990). In 1995, the minimum number along the coast of British Columbia was 1522, including 135 near Goose Island (Watson et al. 1997).

Otters were transplanted from Alaska to Washington in 1969 and 1970; population increased from 36 to 94 between 1981 and 1987 (Matthews and Moseley 1990); 211 were counted in Washington in July 1989 (Jameson, in Riedman and Estes 1990, Reeves et al. 1992).

See also record for subspecies nereis of California (about 2,505 individuals in 2003).

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).

Comments: Foraging occurs throughout the day and night, with periodic resting in between feeding bouts.

The maximum estimated lifespan of sea otters is 23 years in the wild.

(Nowak 1999)

Range lifespan
Status: wild: 23 (high) years.

Average lifespan
Status: wild: 30.0 years.

Average lifespan
Sex: male
Status: captivity: 19.0 years.

Average lifespan
Sex: female
Status: wild: 23.0 years.

Maximum longevity: 27 years (captivity) Observations: There is a delayed implantation and the total gestation time varies from 4 to 12 months. The actual embryonic development takes about 4-5.5 months (Ronald Nowak 2003). It has been suggested that longevity in the wild may be as high as 30 years (Bernhard Grzimek 1990), which is dubious. One wild born female was about 27 years old when she died in captivity (Richard Weigl 2005).

Sea otters have a polygynous mating system. Many males activly defend territories. Disputes are usually settled with splashing and vocal displays, fighting is rare. Males will mate with females that inhabit their territory or seek out estrus females if no territory is established. Males and females bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior.

(McShane et. al. 1995; Estes 1980; Nowak 1999)

Mating System: polygynous

Sea otters can reproduce year round. There are peaks of birth in May-June in the Aleutian Islands and in January-March in the California population. Delayed implantation produces varied gestation times. Pregnancy has been reported to be 4-12 months. Females usually give birth about once a year. Orientation of the fetus may be either caudal or cephalic, although cephalic orientation is more common near birth. A single pup is born weighing 1.4-2.3 kg. Twins occur in 2% of births but only one pup can be raised successfully. Pups typically remain with their mother for 5 to 6 months after birth. Females that lose a pup will go into estrus sooner than if their pup had survived. Females reach sexual maturity at 4 years. Males reach sexual maturity at 5 to 6 years, but may not mate until much later.

(Estes 1980; McShane et. al. 1995; Nowak 1999; Riedman et.al. 1994)

Breeding season: Breeding occurs year round.

Range number of offspring: 2 (high) .

Average number of offspring: 1.

Range gestation period: 4 to 12 months.

Average gestation period: 6 months.

Range weaning age: 2 to 11 months.

Average weaning age: 6 months.

Range age at sexual or reproductive maturity (female): 4 to 6 years.

Range age at sexual or reproductive maturity (male): 4 to 6 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; delayed implantation

Average birth mass: 1868 g.

Average number of offspring: 1.

Females provide all of the parental care for the young. Pups will nurse until weaned, but start to eat solid foods shortly after birth. While the mother is foraging, young will remain on the surface. Pups start diving after two months. Pups learn from their mothers how to forage and what prey items to look for as well as swimming and grooming behaviors. The pup remains dependent on the mother for about 6 to 8 months, but there is considerable variation here also.

(McShane et. al. 1995; Estes 1980; Nowak 1999)

Parental Investment: precocial ; female parental care

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.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 3 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 3
Species With Barcodes: 1

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N4 - Apparently Secure

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2008
  Endangered
  (IUCN 2008)
• 2000
  Endangered
• 1996
  Lower Risk/least concern
  (Baillie and Groombridge 1996)

The fur trade depleted sea otters to about 1000-2000 individuals worldwide by 1911 when the International Fur Seal Treaty between the U.S., Russia, Japan, and Great Britain was established. The U.S. Marine Mammal Protection Act in 1972 provided more support for sea otters. Reintroduction along the west coast of North America and protection from hunting has brought the world population up to 100,000-150,000. The population of California sea otters (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act and will remain so until a population of 2650 is recorded for three consecutive years. The current population is about 2200. There are concerns that a single oil spill could wipe out the California sea otter. In 1989, the Exxon Valdez flooded Prince William Sound, Alaska with oil. An estimated 5,000 sea otters were killed as a result. E.l. nereis is listed in appendix 1 of CITES, the other subspecies are in appendix 2. The IUCN lists Enhydra lutris as endangered.

(Cohn 1998; Nowak 1999; Hilton-Taylor 2000)

US Federal List: threatened

CITES: appendix i

IUCN Red List of Threatened Species: endangered

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Large range in North Pacific; total population has increased to more than 100,000 (430 in Washington); subject to intensive management; vulnerable to oil spills and conflicts with commercial fisheries.

Endangered.

Classified as Endangered (EN) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).

Population

Population Trend

Global Short Term Trend: Increase of 10 to >25%

Comments: Washington population started with 59 individuals translocated from Alaska in 1969-1970; increasing--spring 1996 survey yielded 430 individuals (USFWS 1997 draft revised stock assessment).

Major Threats

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: In various parts of the range, conflicts with commercial fisheries (gill and trammel nets, crab traps) and activities associated with oil and gas exploration, development, and transportation may be the greatest threats. Commercial fisheries are not a threat in Alaska (USFWS 1995 stock assessment). Brody et al. (1996) determined that an oil spill of Exxon Valdez size, occurring at the Monterey Peninsula, California, would kill at least 50% of the total California sea otter population.

In the Aleutian Islands in recent decades, the population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. These data are in general agreement with the hypothesis of increased predation on sea otters (Doroff et al. 2003). Killer whales presumably shifted their diet to include sea otters after populations of their preferred prey, harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), declined.

Since the 1700s, prior to the commercial fur trade, native peoples throughout the otter's range harvested sea otters for their pelts (2). An intensive commercial fur trade, from 1740 until about 1900, resulted in the sea otter being harvested almost to extinction, and by 1900, the sea otter was so rare that commercial harvesting was forced to cease (6). Sea otters were protected by an international treaty in 1911. Since then, numbers have recovered to an extent, but human activities, especially coastal development and marine pollution, now pose a threat to the sea otter (6). In 1989, hundreds, and possibly thousands, of sea otters were killed as a direct result of the Exxon Valdez oil spill in Prince William Sound in Alaska (4). The possibility of another major oil spill poses a continual threat to the sea otter, and could have devastating consequences. Additional threats include entanglement in fishing gear, particularly gill nets, and competition with commercial fisheries for food (6). In the central Aleutian Islands, Alaska, sea otters have declined by as much as 90 percent (4). Evidence indicates that this drastic decline is the result of increased predation by killer whales, which have switched to consuming more sea otters following the collapse of Steller's sea lion and harbour seal populations in the region (4).

Conservation Actions

Restoration Potential: Recovery potential is high if environmental conditions are favorable. In Alaska, otters at the leading edge of an expanding population in an area with abundant food resources and protected water exhibited high adult survival rate, high reproductive rate, and high preweaning survival (Monson and DeGange 1995). Human harvest was the primary source of known mortality of adults.

Management Requirements: See the 1996 Endangered Species Update 13(12) for 20 articles dealing with sea otter conservation and management.

Brody et al. (1996) reviewed the EXXON VALDEZ oil spill and concluded that efforts to rehabilitate otters should be discontinued 20-30 days after a spill.

Draft revised recovery plan for California populations was available in February 2000 (contact U.S. Fish and Wildlife Service, Ventura, California).

Needs: See the 1996 Endangered Species Update 13(12) for 20 articles dealing with sea otter conservation and management.

The sea otter is legally protected in the United States under the Marine Mammal Protection Act and in Canada sea otters are protected under the Species at Risk Act (10). Despite protection and various conservation measures, the Californian population has been slow to recover; a new Recovery Plan by the U.S. Fish and Wildlife Service was currently being developed with the aim of managing damaging human activities to enable the population to recover to a point where it can be removed from the List of Endangered and Threatened Wildlife (11). There have been several successful reintroduction attempts along the west coast of North America, restoring this highly appealing animal to much of its former range (2).

Sea otters compete with commercial fisheries for shellfish and crab.

(Nowak 1999)

The fur of sea otters was of great importance in the fur trade from the mid 1700s to 1911. Pelts would bring as much as $1,125 each.

(Nowak 1999)

Comments: Negatively impacts shellfisheries, though the degree of impact is controversial.

Stewardship Overview: See 1995 draft recovery plan for the California population.