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Adult sea otters typically weigh between 14 and 45&nbsp;kg, making them the heaviest members of the [[mustelid|weasel family]], but one of the smallest marine mammal species. Unlike most marine mammals, the sea otter has an exceptionally thick coat of [[fur]], the densest of all [[mammals]] with up to 400,000 hairs per cm<SUP>2</SUP>. It inhabits shallow coastlines, where it preys mostly upon invertebrates such as [[sea urchin]]s, shellfish, and [[octopus]]es, and on fish.
Adult sea otters typically weigh between 14 and 45&nbsp;kg, making them the heaviest members of the [[mustelid|weasel family]], but one of the smallest marine mammal species. Unlike most marine mammals, the sea otter has an exceptionally thick coat of [[fur]], the densest of all [[mammals]] with up to 400,000 hairs per cm<SUP>2</SUP>. It inhabits shallow coastlines, where it preys mostly upon invertebrates such as [[sea urchin]]s, shellfish, and [[octopus]]es, and on fish.

⚫
Sea otters typically live in coastal waters 15 to 23&nbsp;meters (50 to 75&nbsp;ft) deep,<ref name=silverstein17>Silverstein, p. 17</ref> and usually stay within 1 km of the shore.<ref>Nickerson, p. 49</ref> They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick [[kelp forest]]s, and [[barrier reefs]].<ref>Silverstein, p. 19</ref> The sea otter's historic range is a wide arc across the [[North Pacific]], from northern [[Japan]] and the [[Kuril Islands]] north to the [[Commander Islands]] of Russia, and down the coast of North America to the [[Baja Peninsula]] of Mexico.<ref name=silverstein17>Silverstein p. 17</ref> They are currently found in significant numbers in about two thirds of their original range. Reported sightings of sea otters in the [[San Juan Islands]] and [[Puget Sound]] invariably turn out to be [[northern river otter]]s, which are commonly seen along the seashore.<ref name=haley/>


The sea otter is a classic example of a [[keystone species]]. It is an important predator of sea urchins, which would otherwise inflict extensive damage to [[kelp forest]]s. Kelp forests provide crucial habitat and food for other marine animals, and prevent coastal erosion.
The sea otter is a classic example of a [[keystone species]]. It is an important predator of sea urchins, which would otherwise inflict extensive damage to [[kelp forest]]s. Kelp forests provide crucial habitat and food for other marine animals, and prevent coastal erosion.
Line 100: Line 102:


==Ecology==
==Ecology==
⚫
[[Image:Kelp-forest-Monterey.jpg|thumb|Sea otters keep [[kelp forest]]s healthy by eating animals that graze on kelp.]]
===Distribution and habitat===
⚫
Sea otters typically live in coastal waters 15 to 23&nbsp;meters (50 to 75&nbsp;ft) deep,<ref name=silverstein17>Silverstein, p. 17</ref> and usually stay within 1 km of the shore.<ref>Nickerson, p. 49</ref> They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick [[kelp forest]]s, and [[barrier reefs]].<ref>Silverstein, p. 19</ref> The sea otter's historic range is a wide arc across the [[North Pacific]], from northern [[Japan]] and the [[Kuril Islands]] north to the [[Commander Islands]] of Russia, and down the coast of North America to the [[Baja Peninsula]] of Mexico.<ref name=silverstein17>Silverstein p. 17</ref> They are currently found in significant numbers in about two thirds of their original range.

Reported sightings of sea otters in the [[San Juan Islands]] and [[Puget Sound]] invariably turn out to be [[northern river otter]]s, which are commonly seen along the seashore.<ref name=haley/>
⚫
[[Image:Kelp-forest-Monterey.jpg|thumb|left|Sea otters keep [[kelp forest]]s healthy by eating animals that graze on kelp.]]

===Ecological role===
===Ecological role===
Sea otters are a [[keystone species]]; their presence affects the ecosystem more profoundly than their size and numbers would suggest. Sea otters keep the population of certain invertebrates, particularly the [[sea urchin]], in check. Sea urchins graze on the lower stems of [[kelp]], causing the kelp to drift away and die. Loss of the habitat and nutrients provided by [[kelp forest]]s leads to profound [[Cascade effect (ecology)|cascade effects]] on the marine ecosystem. North Pacific areas that do not have sea otters often turn into [[urchin barren]]s, with abundant sea urchins and no kelp forest.<ref name=adw/>
Sea otters are a [[keystone species]]; their presence affects the ecosystem more profoundly than their size and numbers would suggest. Sea otters keep the population of certain invertebrates, particularly the [[sea urchin]], in check. Sea urchins graze on the lower stems of [[kelp]], causing the kelp to drift away and die. Loss of the habitat and nutrients provided by [[kelp forest]]s leads to profound [[Cascade effect (ecology)|cascade effects]] on the marine ecosystem. North Pacific areas that do not have sea otters often turn into [[urchin barren]]s, with abundant sea urchins and no kelp forest.<ref name=adw/>

Revision as of 21:36, 16 January 2008

For other uses, see Sea otter (disambiguation).

Sea Otter
A sea otter wraps itself in kelp in Morro Bay, California
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Vertebrata
Class:
Mammalia
Order:
Carnivora
Family:
Mustelidae
Subfamily:
Lutrinae
Genus:
Enhydra

Fleming, 1828
Species:
E. lutris
Binomial name
Enhydra lutris
(Linnaeus, 1758)
Modern and historical range

The sea otter (Enhydra lutris) is a marine mammal native to the coasts of the North Pacific, from northern Japan and Kamchatka east across the Aleutian Islands and south to California.

Adult sea otters typically weigh between 14 and 45 kg, making them the heaviest members of the weasel family, but one of the smallest marine mammal species. Unlike most marine mammals, the sea otter has an exceptionally thick coat of fur, the densest of all mammals with up to 400,000 hairs per cm2. It inhabits shallow coastlines, where it preys mostly upon invertebrates such as sea urchins, shellfish, and octopuses, and on fish.

Sea otters typically live in coastal waters 15 to 23 meters (50 to 75 ft) deep,[1] and usually stay within 1 km of the shore.[2] They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick kelp forests, and barrier reefs.[3] The sea otter's historic range is a wide arc across the North Pacific, from northern Japan and the Kuril Islands north to the Commander Islands of Russia, and down the coast of North America to the Baja Peninsula of Mexico.[1] They are currently found in significant numbers in about two thirds of their original range. Reported sightings of sea otters in the San Juan Islands and Puget Sound invariably turn out to be northern river otters, which are commonly seen along the seashore.[4]

The sea otter is a classic example of a keystone species. It is an important predator of sea urchins, which would otherwise inflict extensive damage to kelp forests. Kelp forests provide crucial habitat and food for other marine animals, and prevent coastal erosion.

Between 1741 and 1911, sea otters were hunted extensively for their fur, reducing the world population to 1,000 – 2,000 individuals in a fraction of their historic range. In about two-thirds of its former range, the species has rebounded after an international ban on hunting, conservation efforts, and re-introduction into previously populated areas. The recovery of the sea otter is considered one of the greatest successes in marine conservation. However, it is an endangered species and is particularly vulnerable to oil spills. Populations in the Aleutian Islands and California have either declined or failed to increase in recent years, for reasons that remain unclear.

Taxonomy

The sea otter is the heaviest member of the weasel (Mustelidae) family.[5][6] It is a member of the otter (Lutrinae) subfamily, and the only member of the genus Enhydra. Genetic analysis indicates that the sea otter's closest relatives are the Eurasian otter, spotted-necked otter, cape clawless otter and small-clawed otter.[7] Unlike all other otter species which must come ashore to breed, sea otters can live their entire lives without leaving the water, although they may haul out to land to rest.[8]

There are three recognized subspecies:[5][9]

  • The northern sea otter, Enhydra lutris kenyoni (Wilson, 1991), is native to the Aleutian Islands, and southern Alaska. It has been re-introduced to various locations between Alaska and Oregon.[5] It is also known as the Alaskan sea otter.
  • The southern sea otter, Enhydra lutris nereis (Merriam, 1904), is found off the coast of central California.[5] It is also known as the Californian sea otter.
  • The common sea otter, Enhydra lutris lutris (Linnaeus, 1758), ranges from the Kuril Islands to the Commander Islands in the western Pacific Ocean.[5] It is also known as the Asian sea otter.

The sea otter was formerly sometimes referred to as the "sea beaver,"[10] although it is only distantly related to beavers. The sea otter is not to be confused with the marine otter, a rare otter species native to the west coast of South America.

Biology and behavior

Physical characteristics

A sea otter's thick fur makes its body appear much plumper on land than in the water.
File:Kalan's skeleton.jpg
Skeleton of a sea otter. The hind flippers are larger than the mitten-like front paws.

The sea otter is one of the smallest marine mammal species.[8] Male sea otters weigh 22 to 45 kg (nearly 100 lb) and are 1.2 to 1.5 m (nearly 5 ft) in length. Females are smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length.[11]

The species has exceptionally thick brown or reddish-brown fur with densities of 100,000 to 400,000 hairs/cm2. The head, throat, and chest are lighter in color than the rest of the body. The fur consists of long guard hairs and a layer of dense underfur. When clean, the guard hairs are fully waterproof, allowing the underfur to retain air and remain dry and keeping cold water completely away from the skin.[11] As only the tips get wet, fur can take on a spiky appearance.[12] Unlike other marine mamals, the sea otter has no blubber and it relies on its fur to keep warm.[13] The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct molting season.[14] It can reach and groom the fur on any part of its body, as it has loose skin and an unusually supple skeleton.[15]

The sea otter displays numerous adaptations to its marine environment. The ears and nostrils can close.[16] The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully webbed.[17] The fifth digit on each hind foot is the longest, which facilitates swimming while the animal is on is back but makes walking difficult.[18] The tail is fairly short, thick, slightly flattened, and muscular. The sea otter swims underwater by moving the rear end of its body, including its tail and hind feet, up and down.[17] When at the surface, it lies on its back and moves by sculling its feet and tail from side to side.[19] The front paws are short with retractable claws, with tough pads on the palms that enable gripping slippery prey.[20] On land, the sea otter moves with a lumbering gait.

The sea otter's body is highly buoyant because of its large lung capacity and the air trapped in its fur. Its lung capacity is 2.5 times greater than that of similarly-sized land mammals.[21] The teeth, particularly the molars, are flattened and rounded, designed to crush rather than cut food.[22] The sea otter is the only carnivore with two pairs of lower incisor teeth rather than three.[4] Unlike all other mustelids, the sea otter has no functional anal scent glands.[23] The sea otter's long whiskers and front paws are sensitive and help the otter to find prey by touch.[8]

Hunting and diet

Sensitive whiskers and forepaws enable sea otters to find prey using their sense of touch.

Sea otters have been found to consume over 100 different prey species, including sea urchins, crabs, clams, and octopuses.[24] The individuals within a particular area often differ in their foraging methods and their preferred prey, and tend to follow the same patterns as their mothers.[25]

The sea otter hunts in short dives, often to the sea floor. Dives typically last about one minute and no more than four minutes,[11] although the sea otter can hold its breath for up to five minutes. It is the only marine animal capable of lifting and turning over boulders, which it often does with its front paws when searching for prey.[26] The sea otter may also pluck snails and other organisms from kelp and dig deep into underwater mud for clams.[26] It is the only marine mammal that catches fish with its forepaws rather than with its teeth.[13]

Under each foreleg, the sea otter has a loose pouch of skin that extends across the chest. In this pouch (apparently always the left one), the animal stores collected food to bring to the surface.[4] There, the sea otter eats while floating on its back, using its forepaws as "hands" to tear food apart and bring it to its mouth. It can chew and swallow small mussels with their shells, whereas large mussel shells may be twisted apart.[27] It uses its lower incisor teeth to access the meat in shellfish.[28] To eat large sea urchins, which are mostly covered with spines, the sea otter bites through the underside where the spines are shortest, and licks the soft contents out of the urchin's shell.[27]

The sea otter's use of rocks when hunting and feeding makes it one of the few mammal species to use tools.[29] To open hard shells, it may pound its prey with both paws against a rock on its chest. To pry an abalone off its rock, the sea otter has been observed to hammer the abalone shell using a large stone, at a rate of 45 blows in 15 seconds.[11] Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, can require several dives.[11]

The sea otter has a metabolic rate two or three times that of comparatively sized terrestrial mammals, and must eat an estimated 25% to 38% of its own body weight in food each day.[30][31] It loses heat easily to the cold water environment, and must burn calories to stay warm. It also has the lowest assimilation efficiency of carnivores (82%). Food is digested and passed in as little as three hours.[13]

The sea otter obtains most of its water from food. Unlike most other marine mammals it also drinks sea water, and has relatively large kidneys that enable it to derive fresh water from sea water and excrete wastes as a concentrated urine.[32]

To keep from drifting out to sea, sea otters may sleep holding paws.

Social behavior

Although each adult and independent juvenile forages alone, sea otters tend to rest together in single-sex groups, called rafts. Male rafts are larger than female rafts. The largest raft ever seen contained over 2000 sea otters, although most contain between 10 and 100.[33]

Conflicting data regarding home range and migration of sea otters suggests their movements are dependent on availability of resources. Home ranges may be as large as 5.4 square kilometers, with most animals traveling found within 1 or 2 kilometers of the previous day's location.

The sea otter is diurnal. It has a period of foraging and eating in the morning, starting about an hour before sunrise, then rests or sleeps in mid-day.[34] Foraging resumes for few hours in the afternoon and subsides before sunset.[34] There may be a third foraging period around midnight; females with pups appear to be more inclined to feed at night.[35] Observations of the amount of time a sea otter must spend each day foraging range from 24% to 60%, apparently depending on the availability of food in the area.[36] To keep from drifting out to sea when resting and eating, sea otters may wrap themselves in kelp.[37]

Sea otters also spend much of their time grooming. Grooming consists of cleaning the fur, untangling knots, removing loose fur, rubbing the fur to squeeze out water and introduce air, and blowing air into the fur. To an observer it looks like the animal is scratching, however sea otters are not known to have lice or other parasites in the fur.[38] When eating, the sea otter rolls in the water frequently, apparently to wash food scraps from its fur.[26]

The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a seagull.[39] Females coo when they are apparently content; males may grunt instead.[40] Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream.[39]

Much has been written about the level of devotion of sea otter mothers for their pups. A mother gives her infant almost constant attention, cradling it on her chest away from the cold water and attentively grooming its fur. When searching for food, she leaves her pup floating on the water, sometimes wrapped in kelp to keep it from floating away.[41] If the pup is not sleeping, it cries loudly until she returns.[42] Mothers have been known to carry their pup for days after the pup's death.[43] Occasionally, females have been observed caring for orphaned pups.[44] Males do not help to feed or raise pups.[45]

Reproduction and lifecycle

A mother floats with her pup on her chest. Georg Steller wrote, "They embrace their young with an affection that is scarcely credible."[43]

Sea otters are polygynous: that is, males have multiple female partners. Females in captivity are seen to be polyestrous, coming into estrus in late winter/spring and then again in late summer/autumn. Bonding does occur between the sexes during the female's estrus, which lasts three to five days. During these periods males defend their territories; there is very rarely actual fighting involved, with most disputes being settled by raucous posturing.

A courting pair swims and dives together, with the male twisting and doing corkscrews in the water to let the female know he is interested. The male may swim facedown and swim more quickly than usual. Mating takes place in the water and can be rough, the male biting the female on the side of the face or on the muzzle and sometimes holding her head under water. Females often have characteristic scars on the nose from this.[5][46]

Births occur year-round, with peaks between May and June in northern populations and between January and March in southern populations.[47] Gestation appears to vary from four to twelve months, as the species is capable of delayed implantation followed by four months of pregnancy.[47] In California, sea otters usually breed every year, about twice as often as sea otters in Alaska.[48]

Birth, which usually takes place in the water, typically produces a single pup weighing 1.4 – 2.3 kg.[49] Twins occur in two percent of births, however usually only one of them survives.[5] At birth, the eyes are open and the pup has a thick coat of baby fur. Mothers have been observed to lick and fluff a newborn for hours, and after grooming the pup's fur retains so much air that it floats like a cork and cannot dive. The fluffy baby fur is replaced by adult fur after about three months.

During mating, the male bites the nose of the female, often scarring it. This sea otter also appears to have worn or missing lower teeth, probably caused by crushing hard shellfish.[50]

Nursing lasts six to eight months in California populations, and four to twelve months in Alaska.[51] The milk from a sea otter's two abdominal nipples is more similar in composition to other marine mammals than to other mustelids, with 23% fat, 13% protein, and only 1% lactose. The mother begins to offer bits of prey after one to two months.[52] A pup, with guidance from its mother, practices swimming and diving for several weeks before it is able to reach the sea floor. Initially the objects it retrieves are of little food value, such as brightly colored starfish and pebbles.[4] Pups stay with their mothers for between five and fifteen months, with six months being average. A pup may nurse until it is almost adult size.[49] A mother may be forced to abandon a large pup if she cannot find enough food for it.[53] Pup mortality is high, particularly during an individual's first winter – by one estimate, only 25% of pups survive their first year.[53] Experienced mothers are most successful.[54]

Male sea otters reach sexual maturity around five years of age, but often do not successfully breed until a few years later.[55]. A captive male sired offspring at age 19.[49] Females become sexually mature at around three or four years of age.[55] In the wild, sea otters live to a maximum age of 23 years, and about 10 to 11 years on average.[11] Several captive individuals have lived past 20 years, and a female at the Seattle Aquarium died at the age of 28 years.[56] Sea otters in the wild often develop worn teeth, which may account for their apparently shorter lifespans.[57]

Ecology

Sea otters keep kelp forests healthy by eating animals that graze on kelp.

Ecological role

Sea otters are a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. Sea otters keep the population of certain invertebrates, particularly the sea urchin, in check. Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens, with abundant sea urchins and no kelp forest.[5]

Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems,[58] and similar changes have been observed in the Aleutian and Commander Islands, and the Big Sur coast of California as sea otter populations recovered.[59] However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors.[59] The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries.[59]

Predators of sea otters include orcas and sea lions.[31] Dead sea otters have been found with injuries from shark bites, although there is no evidence that sharks actually eat them.[60] Bald eagles are known to prey on sea otter pups, snatching them from the water surface.[29]

In some areas, the sea otter competes with humans for food, particularly some species of abalone, clams, and crabs. There have been reports of commercial fishermen and others illegally killing sea otters in Alaska and California.[61]

Fur trade

Archaeological evidence indicates that for thousands of years, indigenous peoples have hunted sea otters for food and fur.[10] They took sea otters in moderation; large-scale hunting began in the 1700s when hunters and traders began to arrive from all over the world to meet foreign demand for otter pelts, which were one of the world's most valuable types of fur.[10] The sea otter population is thought to have once been 150,000 to 300,000. It is estimated that approximately one million sea otters were killed between 1741 and 1911.[10]

In the early 1700s, Russians began to hunt sea otters in the Kuril Islands and sold them to China.[10] Russia was also exploring the far northern Pacific at this time, and sent Vitus Bering to map the Arctic coast and find routes from Siberia to North America.[62] In 1741, on his second North Pacific voyage, Bering was shipwrecked off Bering Island in the Commander Islands, where Bering and many of his crew died.[62] The surviving crew members, which included naturalist Georg Steller, discovered sea otters on the beaches of the island and spent the winter hunting sea otters and gambling with otter pelts.[62] They returned to Siberia having killed nearly 1000 sea otters, and were able to command high prices for the pelts.[62] Thus began what is now called The Great Hunt, which would continue for another hundred years.

Aleut men in Unalaska in 1896. The waterproof kayak gear and garments were used to hunt sea otters.

Russian fur-hunting expeditions soon depleted the sea otter populations in the Commander Islands. By 1745, the Russians began to move on to the Aleutian Islands, which were inhabited by the Aleuts.[63] The Russians initially traded with the Aleuts for otter pelts, but later enslaved the Aleuts, taking women and children hostage and torturing and killing Aleut men to force them to hunt. Many Aleuts were either murdered by the Russians or died from diseases that the hunters had introduced.[63] The Aleut population was reduced, by the Russians' own estimate, from 20,000 to 2,000.[64] By the 1760s, the Russians had reached Alaska.

Other nations joined in the hunt in the south. Along the coasts of what is now Mexico and California, Spanish explorers bought sea otter pelts from Native Americans and sold them in Asia.[63] In 1778, British explorer Captain James Cook reached Vancouver Island and bought sea otter furs from the First Nations people.[65] When Cook's ship later stopped at a Chinese port, the pelts rapidly sold at high prices, and were soon known as "soft gold". As word spread, people from all over Europe and North America began to arrive in the Pacific Northwest to trade for sea otter furs.[65] A pelt could be worth as much as $1,125.[5]

Russian hunting expanded to the south, in what is now Washington, Oregon, and California, and the Russians founded what is now the Fort Ross settlement in northern California as their southern headquarters.[65] In the next 29 years, they would kill 50,000 California sea otters.[65]

Eventually, sea otter populations became so depleted that commercial hunting was no longer viable. In the Aleutian Islands, commercial hunting had stopped by 1808.[66] When Russia sold Alaska to the United States in 1867, the Alaska population had recovered to over 100,000, but Americans resumed hunting and quickly extirpated the sea otter again.[66] In 1911, Russia, Japan, Great Britain (for Canada) and the United States signed the Treaty for the Preservation and Protection of Fur Seals, imposing a moratorium on the harvesting of sea otters.[67] So few remained, perhaps only 1,000 – 2,000 individuals in the wild, that many believed the species would become extinct.

Recovery and conservation

In 1938, the population in California was only about 50 animals. It has since rebounded to approximately 3,000.

During the 20th century, sea otter populations rebounded in about two-thirds of their historic range. The remarkable recovery of the species is considered one of the greatest successes in marine conservation.[68] However, in recent years, recovery has been slow or negative in some areas. The IUCN lists sea otter as an endangered species, and describes the significant threats to sea otters as oil pollution, predation by orcas, poaching, and conflicts with fisheries. There have been reports that sea otters have been poached in Russia. Sea otters can drown if entangled in fishing gear.[69]

The most significant threat to sea otters is oil spills.[29] Sea otters are particularly vulnerable, as they rely on their fur to keep warm. When their fur is soaked with oil, it loses its ability to retain air, and the animal quickly dies from hypothermia.[29] The liver, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming.[29]

Prevention of oil spills, and preparation for rescue of otters in the event of a spill, is a major focus of conservation efforts. The small geographic ranges of the sea otter populations in California, Washington, and British Columbia mean that a single major spill could be catastrophic for that state or province.[26][31][70]

Russia

Before the 19th century there were around 20,000 to 25,000 sea otters in the Kuril Islands, with more on Kamchatka and the Commander Islands. After the years of the Great Hunt, the population in these areas, currently part of Russia, was only 750.[71] As of 2004, sea otters have repopulated all of their former habitat in these areas, with an estimated total population of about 27,000. Of these, about 19,000 are in the Kurils, 2000 to 3500 on Kamchatka and another 5000 to 5500 on the Commander Islands.[71] Growth has slowed slightly, suggesting that the numbers are reaching carrying capacity.[71] The success of the sea otter's recovery in Russia has been credited to large-scale and long-term protection, enlargement of the species's range, and human emigration from the islands.[71]

Alaska

In the 1930s, sea otter colonies were discovered in Alaska's Aleutian Islands and Prince William Sound. A sanctuary was created in Amchitka Island, whose sea otter population grew to outstrip its supply of prey.[72] By the mid-1960s, Amchitka Island was being used a site for nuclear testing, which eventually killed many sea otters in the area. In advance of a major test in 1968, the U.S. Atomic Energy Commission agreed to move hundreds of the animals to other parts of the coast. Seven hundred sea otters were transplanted in the 1960s and 1970s, with survival rates improving as scientists became more knowledgeable about how to safely transport the animals.[73] In 1973, the sea otter population in Alaska was estimated at between 100,000 and 125,000 animals.[74]

Recent declines

In recent decades, however, the sea otter population the Aleutian Islands of western Alaska has plummeted. In the 1980s, the area was home to an estimated 55,000 to 100,000 sea otters, but the population fell to around 6,000 animals by 2000.[75] One controversial hypothesis is that orcas have been eating the otters. The evidence in support of this explanation is circumstantial: It is unlikely that the otters have been dying from disease or starvation, as few bodies of sick or emaciated otters have been recovered.[75] Also, populations have declined in areas of open water frequented by orcas, but not in nearby lagoons where orcas are absent.[76]

File:OilSheenFromValdezSpill.jpeg
In the wake of the Exxon Valdez oil spill, heavy sheens of oil covered large areas of Prince William Sound.

Some Alaska orcas specialize in preying on marine mammals and others on fish. The orcas that prefer marine mammal prey usually attack seals, sea lions, and small cetaceans, and have occasionally been seen preying on grey whale calves. The small, furry sea otter offers little nutrition for an orca, however orcas may have started eating otters due to shortages of their usual, much larger, prey. The region's population of large whales was decimated by commercial whaling in the 1960s. Then stocks of harbor seals and Steller sea lions experienced massive declines in the 1970s and 1980s, respectively, which may have forced orcas to seek smaller prey.[77] The theory that orca predation has been responsible for this cascade of declines remains controversial, and so far there has been no direct evidence that orcas prey on sea otters to any significant extent.[76]

The 1989 Exxon Valdez oil spill devastated the sea otter population in Prince William Sound. Over 1,000 oiled sea otter carcasses were recovered,[78] with the actual number of deaths estimated to be several times that number.[26][79] Approximately 350 oiled sea otters were rescued, and over the next five months given intensive rehabilitation.[80] Each otter was tranquilized and thoroughly washed and dried. Those which had swallowed a lot of oil were treated with activated charcoal. The effort saved about 200 of the 350 rescued sea otters, although many later died after being released.[80] A 2006 report from the Exxon Valdez Oil Spill Trustee Council named the sea otter as one of several species still being affected by the lingering oil in the area.[81]

Current status

As of 2006, there are an estimated 73,000 sea otters in Alaska. In August 2005, the "southwest Alaska Distinct Population Segment" of the sea otter was listed as "threatened" under the Endangered Species Act.[82] A little over a year later, the Arizona-based Center for Biological Diversity filed a lawsuit arguing that the U.S. Fish and Wildlife Service had failed to designate critical habitat for the species, as required by the Endangered Species Act. [83]

British Columbia, Washington, and Oregon

Between 1969 and 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island, British Columbia. They established a healthy population, estimated to be over 3,000 as of 2004, and their range is now from Tofino to Cape Scott.[84] However, the First Nations people in the area had not been consulted before the relocations took place. Although the transplanted sea otters improved the general health of the ecosystem, they depleted shellfish that local indigenous communities had relied upon, and many came to regret the return of the otters.[85]

In 1989, a separate colony was discovered in the central B.C. coast. It is not known if this colony, which had a size of about 300 animals in 2004, was founded by transplanted otters or by survivors of the fur trade.[84] In Canada, the sea otter is considered a threatened species and is protected under the federal Species at Risk Act.[58]

In 1969 and 1970, 59 sea otters were transplanted from Amchitka Island to Washington State. Between 2000 and 2004, annual surveys have counted between 504 and 743 sea otters.[70] The state has listed the sea otter as an endangered species since 1981.[70]

Attempts were made to transplant 93 sea otters to the Oregon coast in the 1970s, however none have been seen since the early 1980s.[73] It is not known if they died or moved away.[73]

California

The pre-fur trade population in California is believed to have been 16,000.[86] In 1938, biologists discovered a group of about 50 southern sea otters in a remote part of the coast south of Carmel, California. With conservation efforts, this group has since grown and expanded its range.[78] However, recovery has been fairly slow. Its average growth rate between 1914 and 1984 was only 5%, and fluctuated or declined in the late 1990s.[87] The southern sea otter was listed under the Endangered Species Act as an threatened subspecies in 1977. A survey taken in the spring of 2007 counted over 3,000 sea otters in California.[86]

A raft of sea otters at Moss Landing, California

The causes of the recent difficulties for California's sea otters are not well understood. Unusually high mortality rates amongst adult and young adult otters, particularly females, have been reported, with disease a possible but not certain cause.[86] Parasites and infectious diseases cause 40% of sea otter deaths in California.[78] In recent years, pathogens from urban cats may have been responsible for sea otter deaths. According to a 2002 study in California, otters near heavy freshwater flows — storm drains and river mouths — are three times more likely to have been infected by the often-fatal Toxoplasma gondii parasite than otters from areas where runoff is light.[88]

In a survey of 233 live and dead otters from Santa Barbara to Half Moon Bay, California, 76 percent of sea otters near heavy freshwater outflows had antibodies to Toxoplasma gondii. In the general sea otter population, 42 percent of live otters surveyed had antibodies to the parasite, an almost certain sign of infection. Domestic and wild cats are the only animals known to shed the parasite's eggs in their droppings.[88] The droppings can then be washed into streams and storm drains by rain, or after being flushed down the toilet. Cat owners are encouraged to dispose of droppings in the trash rather than flushing them.[89]

Notes

  1. ^ a b Silverstein, p. 17 Cite error: The named reference "silverstein17" was defined multiple times with different content (see the help page).
  2. ^ Nickerson, p. 49
  3. ^ Silverstein, p. 19
  4. ^ a b c d Haley, Delphine, ed. (1986). "Sea Otter". Marine Mammals of Eastern North Pacific and Arctic Waters (2nd edition ed.). Seattle, Washington: Pacific Search Press. ISBN 0-931397-14-6. {{cite book}}: |edition= has extra text (help)
  5. ^ a b c d e f g h i "Enhydra Lutis". Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved 2007-11-24.
  6. ^ The giant otter is longer, but significantly slimmer.
  7. ^ Koepfli, K.-P (1998). "Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome b sequences". Journal of Zoology. 246 (4): 401–416. Retrieved 2007-12-29. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  8. ^ a b c VanBlaricom, p. 11
  9. ^ "Enhydra lutris". Integrated Taxonomic Information System. 18 March. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  10. ^ a b c d e Silverstein, p. 34
  11. ^ a b c d e f "Sea Otter, Enhydra lutris at MarineBio.org". Retrieved 2007-11-23.
  12. ^ Kenyon, p. 7
  13. ^ a b c Nickerson, p. 21
  14. ^ Kenyon, p. 37-39
  15. ^ Love, p. 21 and 28
  16. ^ Silverstein, p. 13
  17. ^ a b Love, p. 21
  18. ^ Kenyon, p. 70
  19. ^ Love, p. 22
  20. ^ Silverstein, p. 11
  21. ^ http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=A0A7
  22. ^ Kenyon, p. 43
  23. ^ Kenyon, p. 4
  24. ^ VanBlaricom, pp. 18-22
  25. ^ VanBlaricom, p. 29
  26. ^ a b c d e Reitherman, Bruce (Producer and photographer). Waddlers and Paddlers: A Sea Otter Story - Warm Hearts & Cold Water (Documentary). U.S.A.: PBS. {{cite AV media}}: Cite has empty unknown parameters: |accessmonth=, |accessyear=, |month2=, and |date2= (help); Unknown parameter |year2= ignored (help)
  27. ^ a b VanBlaricom, p. 22
  28. ^ "Sea otter". BBC. Retrieved 2007-12-31.
  29. ^ a b c d e "Sea otter AquaFact file". Vancouver Aquarium Marine Science Centre. Retrieved 2007-12-05.
  30. ^ VanBlaricom, p. 17
  31. ^ a b c "Sea Otter" (PDF). British Columbia Ministry of Environment, Lands and Parks. October 1993. Retrieved 2007-12-13.
  32. ^ Ortiz, Rudy M. (2001). "Osmoregulation in Marine Mammals". Journal of Experimental Biology. 204: 1831–1844. Retrieved 2007-12-23. {{cite journal}}: Cite has empty unknown parameters: |coauthors= and |month= (help)
  33. ^ Love, p. 49
  34. ^ a b Love, p. 69
  35. ^ Love, p. 70
  36. ^ Love, p. 70 - 71
  37. ^ VanBlaricom, p. 45
  38. ^ Kenyon, p. 76
  39. ^ a b Kenyon, p. 77
  40. ^ Kenyon, p, 78 - 79
  41. ^ Silverstein, p. 31
  42. ^ Silverstein, p. 28
  43. ^ a b Love, p. 58
  44. ^ Love, p. 59
  45. ^ Silverstein, p. 27
  46. ^ At least one female is known to have died from an infected nose. (Love, p. 52)
  47. ^ a b Love, p. 54
  48. ^ Silverstein, p. 30
  49. ^ a b c Nowak, Roland M. (1991). Walker's Mammals of the World Volume II. Baltimore and London: The John Hopkins University Press. pp. 1141–1143. ISBN 0-8018-3970-X. {{cite book}}: Unknown parameter |Edition= ignored (|edition= suggested) (help)
  50. ^ Love, p. 74
  51. ^ Silverstein, p. 31
  52. ^ Silverstein, p. 32
  53. ^ a b Love, p. 63 Cite error: The named reference "love63" was defined multiple times with different content (see the help page).
  54. ^ Love, p. 62
  55. ^ a b Love, p. 53
  56. ^ VanBlaricom, p. 40-41
  57. ^ VanBlaricom, p. 41
  58. ^ a b "Aquatic Species at Risk - Species Profile - Sea Otter". Fisheries and Oceans Canada. Retrieved 2007-11-29.
  59. ^ a b c VanBlaricom, p. 33
  60. ^ Nickerson, p. 21
  61. ^ Nickerson, p. 47-48
  62. ^ a b c d Silverstein, p. 35
  63. ^ a b c Silverstein, p. 37
  64. ^ Gedney, Larry. "The Aleut and the Otter".
  65. ^ a b c d Silverstein, p. 38
  66. ^ a b Silverstein, p. 40
  67. ^ VanBlaricom, p. 50
  68. ^ VanBlaricom, p. 53
  69. ^ Template:IUCN2006
  70. ^ a b c "Final Washington State Sea Otter Recovery Plan". Washington Department of Fish and Wildlife. Retrieved 2007-11-29.
  71. ^ a b c d Kornev S.I., Korneva S.M. (2004) Population dynamics and present status of sea otters (Enhydra lutris) of the Kuril Islands and southern Kamchatka. Marine Mammals of the Holarctic, Proceedings of 2004 conference. p. 273-278.
  72. ^ Silverstein, p. 43
  73. ^ a b c Silverstein, p. 44 Cite error: The named reference "silverstein44" was defined multiple times with different content (see the help page).
  74. ^ Nickerson, p. 46
  75. ^ a b "Aleutian Sea Otter population falls 70% in eight years". CNN. July 6, 2000. Retrieved 2007-12-04.
  76. ^ a b Schrope, Mark (15 February 2007). "Food chains: Killer in the kelp". Nature. 445: 703–705.
  77. ^ Chanut, Françoise (May 9, 2005). "Lacking a decent meal, killer whales reach for the popcorn". Currents online. University of California at Santa Cruz. {{cite web}}: Unknown parameter |acessdate= ignored (|access-date= suggested) (help)
  78. ^ a b c "Sea Otters at Risk". Monterey Bay Aquarium. Retrieved 2007-12-05.
  79. ^ Estimates vary from 2,000 to 6,000 sea otters
  80. ^ a b Silverstein, p. 55
  81. ^ "Damage of Exxon Valdez endures". Associated Press. Jan 31, 2007. Retrieved 2001-12-25.
  82. ^ "Sea Otters – Southwest Alaska Sea Otter Recovery Team (SWAKSORT)". U.S. Fish and Wildlife Service – Alaska. Retrieved 2008-01-15.
  83. ^ Pemberton, Mary (Tuesday, December 19, 2006; 10:27 PM). "Lawsuit Seeks to Sheild Alaska Sea Otter". The Washington Post. Retrieved 2008-01-05. {{cite news}}: Check date values in: |date= (help); Cite has empty unknown parameter: |coauthors= (help)
  84. ^ a b Barrett-Lennard, Lance (October 20, 2004). "British Columbia: Sea Otter Research Expedition". Vancouver Aquarium. Retrieved 2007-12-11.
  85. ^ Okerlund, Lana (October 4, 2007). "Too Many Sea Otters?". Retrieved 2007-01-15.
  86. ^ a b c Leff, Lisa (June 15, 2007). "California otters rebound, but remain at risk". Associated Press. Retrieved 2007-12-25.
  87. ^ "Sea Otters: Species Description". Alaska SeaLife Center. Retrieved 2007-01-15.
  88. ^ a b "Parasite in cats killing sea otters". NOAA magazine. National Oceanographic and Atmospheric Administration. January 21, 2003. Retrieved 2007-11-24.
  89. ^ "Monterey Bay's sea otter sleuth". Via Magazine. Retrieved 2007-12-05.

Bibliography

  • Kenyon, Karl W. (1969). The Sea Otter in the Eastern Pacific Ocean. Washington, D.C.: U.S. Bureau of Sport Fisheries and Wildlife.
  • Love, John A. (1992). Sea Otters. Golden, Colorado: Fulcrum Publishing. ISBN 1-55591-123-4. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  • Nickerson, Roy (1989). Sea Otters, a Natural History and Guide. San Francisco, CA: Chronicle Books. ISBN 0-87701-567-8.
  • Silverstein, Alvin (1995). The Sea Otter. Brookfield, Connecticut: The Millbrook Press, Inc. ISBN 1-56294-418-5. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • VanBlaricom, Glenn R. (2001). Sea Otters. Stillwater, MN: Voyageur Press Inc. ISBN 0-89658-562-X.
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