Sea otter
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Clayoquot
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/* External links */ rm Defenders of Wildlife link again; hasn't improved since the last time we removed it
{{otheruses}}
{{Taxobox
| name = Sea Otter
| status = EN
| trend = down
| status_system = iucn2.3
| image = sea otter cropped.jpg
|image_caption = A sea otter wraps itself in [[kelp]] in [[Morro Bay, California]].
| image_width = 250px
| regnum = [[Animal]]ia
| phylum = [[Chordata]]
| subphylum = [[Vertebrate|Vertebrata]]
| classis = [[Mammal]]ia
| ordo = [[Carnivora]]
| familia = [[Mustelidae]]
| subfamilia = [[Lutrinae]]
| genus = '''''Enhydra'''''
| genus_authority = [[John Fleming (naturalist)|Fleming]], 1828
| species = '''''E. lutris'''''
| binomial = ''Enhydra lutris''
| binomial_authority= ([[Carl Linnaeus|Linnaeus]], 1758)
| range_map = Sea-otter-map.jpg
| range_map_width = 250px
| range_map_caption = Modern and historical range
}}
The '''sea otter''' (''Enhydra lutris'') is a [[marine mammal]] native to the coasts of the northern and eastern [[Pacific Ocean|North Pacific Ocean]]. Adult sea otters typically weigh between 14 and 45 [[Kilogram|kg]] (30 to 100 [[Pound (mass)|lb]]), making them the heaviest members of the [[Mustelidae|weasel family]], but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of [[fur]], the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.
The sea otter inhabits nearshore environments where it can quickly dive to the sea floor to forage. It preys mostly upon marine invertebrates such as [[sea urchin]]s, various [[mollusk]]s and [[crustacean]]s, and some species of [[fish]]. Its foraging and eating habits are noteworthy in several respects. First, its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. In most of its range, it is a [[keystone species]], controlling sea urchin populations which would otherwise inflict extensive damage to [[kelp forest]] ecosystems. Finally, its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries.
Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 1741 and 1911, and the world population fell to 1,000–2,000 individuals in a fraction of their historic range. A subsequent international ban on hunting, conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species now occupies about two-thirds of its former range. The recovery of the sea otter is considered an important success in [[marine conservation]], although populations in the [[Aleutian Islands]] and [[California]] have recently declined or have plateaued at depressed levels. For these reasons (as well as its particular vulnerability to [[oil spill]]s) the sea otter remains classified as an [[endangered species]].
==Taxonomy==
The first scientific description of the sea otter is contained in the field notes of [[Georg Steller]] from 1751, and the species was described by [[Carl Linnaeus|Linnaeus]] in his ''[[Systema Naturae]]'' of 1758.<ref name=wdfw/> Originally named ''Lutra marina'', it underwent numerous name changes before being accepted as ''Enhydra lutris'' in 1922.<ref name=love9/> The generic name ''Enhydra'', derives from the [[Ancient Greek]] ''en''/εν "in" and ''hydra''/ύδρα "water",<ref name="Liddell 1980">{{cite book | author = [[Henry Liddell|Liddell, Henry George]] and [[Robert Scott (philologist)|Robert Scott]] | year = 1980 | title = [[A Greek-English Lexicon]] (Abridged Edition) | publisher = [[Oxford University Press]] | location = United Kingdom | id = ISBN 0-19-910207-4}}</ref> meaning "in the water", and the [[Latin]] word ''lutris'', meaning "otter".<ref>Nickerson, p. 19</ref> It was formerly sometimes referred to as the "sea beaver",<ref name=silverstein34>Silverstein, p. 34</ref> although it is only distantly related to [[beaver]]s. It is not to be confused with the [[marine otter]], a rare otter species native to the southern west coast of [[South America]]. A number of other otter species, while predominantly living in fresh water, are commonly found in marine coastal habitats as well.
===Evolution===
[[Image:Four sea otters.JPG|thumb|right|230px|Although it is a relatively new marine mammal lineage, the sea otter can live in the ocean at all stages of life.]]
The sea otter is the heaviest member of the family [[Mustelidae]],<ref name=adw/><ref>The [[giant otter]] is longer, but significantly slimmer.</ref> a diverse group that includes the thirteen [[otter]] species and terrestrial animals such as [[weasel]]s, [[badger]]s, and [[mink]]s. It is unique among the mustelids in not making [[lair|den]]s or [[burrow]]s, in having no functional [[anal scent glands]],<ref>Kenyon, p. 4</ref> and in being able to live its entire life without leaving the water.<ref name=vanblaricom11>VanBlaricom, p. 11</ref> The only member of the genus ''Enhydra'', the sea otter is so different from other mustelid species that as recently as 1982, some scientists believed it was more closely related to the [[earless seal]]s.<ref name=koepfli>{{cite journal |last= Koepfli|first=K.-P |authorlink= |coauthors= Wayne, R.K.|year= 1998|month=December |title=Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome b sequences |journal=Journal of Zoology |volume= 246|issue=4 |pages=401–416 |id= |doi= 10.1111/j.1469-7998.1998.tb00172.x|accessdate=2007-12-29}}</ref> [[Molecular phylogeny|Genetic]] analysis indicates that the sea otter and its closest [[Extant taxon|extant]] relatives, which include the African [[speckle-throated otter]], [[Eurasian otter]], [[African Clawless Otter|African clawless otter]] and [[oriental small-clawed otter]], shared an ancestor approximately 5 million years ago (mya).<ref name=koepfli2008>{{cite journal |author= Koepfli, Klaus-Peter et al. |title=Multigene phylogeny of the Mustelidae: resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation |doi= 10.1186/1741-7007-6-10 | journal=BMC Biology |year= 2008 |month= February |day=14 |volume=6 |issue=10 |pages=10 }}</ref>
Fossil evidence indicates that the ''Enhydra'' lineage became isolated in the North Pacific approximately 2 mya, giving rise to the now-extinct ''Enhydra macrodonta'' and the modern sea otter, ''Enhydra lutris''.<ref name=love9>Love, p. 9</ref> The sea otter evolved initially in northern [[Hokkaidō]] and Russia, then spread east to the [[Aleutian Islands]], mainland [[Alaska]], and down the North American coast.<ref>Love, pp. 15–16</ref> In comparison to [[cetacea]]ns, [[sirenian]]s, and [[pinniped]]s, which entered the water approximately 50 mya, 40 mya, and 20 mya, respectively, the sea otter is a relative newcomer to a marine existence.<ref>Love, pp. 4–6</ref> In some respects, however, the sea otter is more fully aquatically adapted than pinnipeds, which must haul out on land or ice to give birth.<ref>Love, p. 6</ref>
===Subspecies===
There are three recognized subspecies, which vary in body size and in some skull and dental characteristics:<ref name=adw>{{cite web |url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html|title=Enhydra Lutis|accessdate=2007-11-24 |format= |work= Animal Diversity Web|publisher=University of Michigan Museum of Zoology}}</ref><ref>{{ITIS|ID=180547|taxon=Enhydra lutris|year=2006|date=18 March}}</ref>
* The '''common sea otter, ''E. l. lutris''''' (Linnaeus, 1758), ranges from the [[Kuril Islands]] to the [[Commander Islands]] in the western Pacific Ocean.<ref name=adw/> Also known as the Asian sea otter, it is the largest subspecies with a wide skull and short nasal bones.<ref name=Wilson>{{cite journal|title=Geographic Variation in Sea Otters, Enhydra lutris|author=Wilson, Don. E. et al|
journal=Journal of Mammalogy|volume=72|issue = 1 |year= 1991|month= February|pages= 22–36|url=http://links.jstor.org/sici?sici=0022-2372%28199102%2972%3A1%3C22%3AGVISOE%3E2.0.CO%3B2-M&size=LARGE&origin=JSTOR-enlargePage|doi=10.2307/1381977
}}</ref>
* The '''southern sea otter, ''E. l. nereis''''' (Merriam, 1904), is found off the coast of central [[California]].<ref name=adw/> Also known as the Californian sea otter, it has a narrower skull with a long [[rostrum (anatomy)|rostrum]] and small teeth.<ref name=Wilson/>
* The '''northern sea otter, ''E. l. kenyoni'''''<ref>Sea otter researcher Karl W. Kenyon, after whom the subspecies is named, was never convinced that ''E. l. kenyoni'' was a distinct subspecies.{{cite web|url=http://www.starrsites.com/acsmb/Soundings/archives/Soundings0706.pdf|title=Soundings: The Newsletter of the Monterey Bay Chapter of ACS|publisher=American Cetacean Society Monterey Bay Chapter|date= June 2007|accessdate=2008-01-22}}</ref> (Wilson, 1991), also known as the Alaskan sea otter, is native to the Aleutian Islands and mainland Alaska,<ref name=Wilson/> but has since been re-introduced to various locations from Alaska to [[Oregon]].<ref name=adw/> While intermediate between the other subspecies in most characteristics, it has longer [[mandible]] bones.
==Physical characteristics==
[[Image:Seaotterrocks.jpg|thumb|right|250px|A sea otter's thick fur makes its body appear much plumper on land than in the water.]]
The sea otter is one of the smallest [[marine mammal]] species.<ref name=vanblaricom11>VanBlaricom, p. 11</ref> Male sea otters weigh 22 to 45 kg (49 to 99 lb) and are 1.2 to 1.5 [[m]] (4 to 5 ft) in length. Females are smaller, weighing 14 to 33 kg (30 to 73 lb) and measuring 1.0 to 1.4 m (3 [[Foot (unit)|ft]] 3 [[Inch|in]] to 4 ft 7 in) in length.<ref name=marinebio/>
Unlike other marine mammals, the sea otter has no [[blubber]] and relies on its exceptionally thick fur to keep warm.<ref name=nickerson21>Nickerson, p. 21</ref> With up to 150 thousand strands of hair per square centimeter (nearly one million per sq in), its [[fur]] is the most dense of any animal.<ref>Silverstein, p. 14</ref> The fur consists of long waterproof guard hairs and short underfur; the guard hairs keep the dense underfur layer dry. Cold water is thus kept completely away from the skin and heat loss is limited.<ref name=marinebio>{{cite web |url=http://marinebio.org/species.asp?id=157 |title= Sea Otter, Enhydra lutris at MarineBio.org|accessdate=2007-11-23 |format= |work= }}</ref> The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct [[molt]]ing season.<ref>Kenyon, pp. 37–39</ref> As the ability of the guard hairs to repel water depends on utmost cleanliness, the sea otter has the ability to reach and groom the fur on any part of its body, taking advantage of its loose skin and an unusually supple [[skeleton]].<ref>Love, p. 21 and 28</ref> The coloration of the [[pelage]] is usually deep brown with sliver-gray speckles, however it can range from yellowish or grayish brown to almost black.<ref name = love27>Love, p. 27</ref> In adults, the head, throat, and chest are lighter in color than the rest of the body.<ref name = love27/>
The sea otter displays numerous adaptations to its marine environment. The nostrils and small ears can close.<ref name = "Silverstein_p13">Silverstein, p. 13</ref> The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully webbed.<ref name=love21>Love, p. 21</ref> The fifth digit on each hind foot is longest, facilitating swimming while on its back, but making walking difficult.<ref name = "Kenyon_p70">Kenyon, p. 70</ref> The tail is fairly short, thick, slightly flattened, and muscular. The front paws are short with retractable claws, with tough pads on the palms that enable gripping slippery prey.<ref>Silverstein, p. 11</ref>
[[Image:Kalan's skeleton.jpg|thumb|left|250px|Skeleton of a sea otter. The hind flippers are larger than the mitten-like front paws.]]
The sea otter propels itself underwater by moving the rear end of its body, including its tail and hind feet, up and down,<ref name=love21>Love, p. 21</ref> and is capable of speeds of up to 9 [[km]]/h (5.6 [[Miles per hour|mph]]).<ref name=adw/> When underwater, its body is long and streamlined, with the short forelimbs pressed closely against the chest.<ref>Kenyon, p. 62</ref> When at the surface, it usually floats on its back and moves by sculling its feet and tail from side to side.<ref>Love, p. 22 </ref> At rest, all four limbs can be folded onto the torso to conserve heat, whereas on particularly hot days the hind feet may be held underwater for cooling.<ref>VanBlaricom, p. 64</ref> The sea otter's body is highly [[buoyant]] because of its large [[lung capacity]] – about 2.5 times greater than that of similarly-sized land mammals<ref>{{cite web|url=http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=A0A7 |title=USFWS Species Profile: Southern sea otter (''Enhydra lutris nereis'')|accessdate=2008-02-23}}</ref> – and the air trapped in its fur. The sea otter walks with a clumsy rolling gait on land, and can run in a bounding motion.<ref name = "Kenyon_p70"/>
Long, highly sensitive [[vibrissa|whiskers]] and front paws help the sea otter find prey by [[touch]] when waters are dark or murky.<ref name=vanblaricom11>VanBlaricom, p. 11 and 21</ref> Researchers have noted that when they approach in plain view, sea otters react more rapidly when the wind is blowing towards the animals, indicating that the sense of [[Olfaction|smell]] is more important than [[Visual perception|sight]] as a warning sense.<ref>Kenyon, p. 55</ref> Other observations indicate that the sea otter's sense of sight is useful above and below the water, although not as good as that of seals.<ref>Love, p. 23</ref> Its [[hearing (sense)|hearing]] is neither particularly acute nor poor.<ref>Kenyon, p. 56</ref>
An adult's 32 [[teeth]], particularly the [[Molar (tooth)|molars]], are flattened and rounded, designed to crush rather than cut food.<ref>Kenyon, p. 43</ref> [[Pinniped|Seal]]s and sea otters are the only [[carnivore]]s with two pairs of lower [[incisor]] teeth rather than three;<ref>Love, p. 74</ref> the adult [[dentition|dental formula]] is:<ref>Kenyon, p. 47</ref> {{dentition2|3.1.3.1|2.1.3.2}}
The sea otter has a [[metabolic rate]] two or three times that of comparatively sized [[Terrestrial animal|terrestrial]] mammals. It must eat an estimated 25 to 38% of its own body weight in food each day in order to burn the calories necessary to counteract the loss of heat due to the cold water environment.<ref>VanBlaricom, p. 17</ref><ref name=wlap>{{cite web|url=http://wlapwww.gov.bc.ca/wld/documents/otter.pdf|title=Sea Otter|publisher=British Columbia Ministry of Environment, Lands and Parks|date=October 1993|accessdate=2007-12-13}}</ref> Its digestive efficiency is estimated at 80 to 85%,<ref>Love, p.24</ref> and food is digested and passed in as little as three hours.<ref name=nickerson21>Nickerson, p. 21</ref> Most of its need for water is met through food, although, in contrast to most other marine mammals, it also drinks seawater. Its relatively large [[kidney]]s enable it to derive fresh water from sea water and excrete concentrated urine.<ref>{{cite journal|title=Osmoregulation in Marine Mammals|url=http://jeb.biologists.org/cgi/content/full/204/11/1831|last= Ortiz|first=Rudy M. |authorlink= |coauthors= |year= 2001|month= |journal= Journal of Experimental Biology|volume= 204|issue= |pages=1831–1844 |accessdate= 2007-12-23|pmid=11441026}}</ref>
==Behavior==
[[Image:sea otter with sea urchin.jpg|thumb|right|Sensitive [[Vibrissa|whiskers]] and forepaws enable sea otters to find prey using their sense of [[touch]].]]
The sea otter is [[Diurnality|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.<ref name=love69>Love, pp. 69–70</ref> Foraging resumes for a few hours in the afternoon and subsides before sunset, and there may be a third foraging period around midnight.<ref name=love69/> Females with pups appear to be more inclined to feed at night.<ref name=love69/> 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.<ref>Love, pp. 70–71</ref>
The sea otter spends much of its time grooming, which 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 appears as if the animal is scratching, however sea otters are not known to have [[lice]] or other parasites in the fur.<ref>Kenyon, p. 76</ref> When eating, the sea otter rolls in the water frequently, apparently to wash food scraps from its fur.<ref name=wp/>
===Foraging===
The sea otter hunts in short dives, often to the [[sea floor]]. Although it can hold its breath for up to five minutes,<ref name = "Silverstein_p13"/> dives typically last about one minute and no more than four.<ref name=marinebio/> 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.<ref name=wp>{{cite video |people=Reitherman, Bruce (Producer and photographer) |date2= |month2= |year2= 1993 |title=Waddlers and Paddlers: A Sea Otter Story–Warm Hearts & Cold Water |url= |format= |medium= Documentary |publisher= [[Public Broadcasting Service|PBS]]|location= U.S.A.|accessdate= |accessmonth= |accessyear= |time= |quote= }}</ref> The sea otter may also pluck [[snail]]s and other organisms from kelp and dig deep into underwater mud for [[clam]]s.<ref name=wp/> It is the only marine mammal that catches [[fish]] with its forepaws rather than with its teeth.<ref name=nickerson21>Nickerson, p. 21</ref>
Under each foreleg, the sea otter has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left one), the animal stores collected food to bring to the surface.<ref name=haley>{{cite book|editor=Haley, Delphine|title=Marine Mammals of Eastern North Pacific and Arctic Waters|edition=2nd edition|chapter=Sea Otter|date=1986|location=Seattle, Washington|publisher=Pacific Search Press|ISBN=0-931397-14-6}}</ref> There, the sea otter eats while floating on its back, using its forepaws to tear food apart and bring it to its mouth. It can chew and swallow small [[mussel]]s with their shells, whereas large mussel shells may be twisted apart.<ref name=vanblaricom22>VanBlaricom, p. 22</ref> It uses its lower [[incisor]] teeth to access the meat in shellfish.<ref name=bbc>{{cite web|title=Sea otter|url=http://www.bbc.co.uk/nature/wildfacts/factfiles/600.shtml|publisher=[[BBC]]|accessdate=2007-12-31}}</ref>
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.<ref name=vanblaricom22>VanBlaricom, p. 22</ref>
The sea otter's use of rocks when hunting and feeding makes it one of the few [[mammal]] species to use tools.<ref name=vanaqua/> 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, it hammers the abalone shell using a large stone, with observed rates of 45 blows in 15 seconds.<ref name=marinebio/> Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, requires multiple dives.<ref name=marinebio/>
[[Image:Sea otters holding hands.jpg|thumb|left|To keep from drifting apart, sea otters may sleep holding paws.<ref name=tyee1/> Note the high buoyancy of the animals' bodies.]]
===Social structure===
Although each adult and independent juvenile forages alone, sea otters tend to rest together in single-sex groups called ''rafts''. A raft typically contains 10 to 100 animals, with male rafts being larger than female ones.<ref name=love49>Love, p. 49</ref> The largest raft ever seen contained over 2000 sea otters. To keep from drifting out to sea when resting and eating, sea otters may wrap themselves in [[kelp]].<ref>VanBlaricom, p. 45</ref>
A male sea otter is most likely to mate if he maintains a breeding territory in an area that is also favored by females.<ref name= vb4245>VanBlaricom, pp. 42–45</ref> As autumn is the peak breeding season in most areas, males typically defend their territory only from spring to autumn.<ref name= vb4245/> During this time, males patrol the boundaries of their territories to exclude other males,<ref name= vb4245/> although actual fighting is rare.<ref name=love49/> Adult females move freely between male territories, where they outnumber adult males by an average of five to one.<ref name= vb4245/> Males who do not have territories tend to congregate in large male-only groups,<ref name= vb4245/> and swim through female areas when searching for a mate.<ref>Love, p. 50</ref>
The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a [[seagull]].<ref name=kenyon77>Kenyon, p. 77</ref> Females coo when they are apparently content; males may grunt instead.<ref>Kenyon, pp. 78–79</ref> Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream.<ref name=kenyon77>Kenyon, p. 77</ref>
Although sea otters can be playful and sociable, they are not considered to be truly [[social animal]]s.<ref name=Silverstein61>Silverstein, p. 61</ref> They spend much time alone, and each adult can meet its own needs in terms of hunting, grooming, and defense.<ref name=Silverstein61/>
===Reproduction and lifecycle===
[[Image:Sea otter with injured nose.JPG|thumb|right|During mating, the male bites the nose of the female, often bloodying and scarring it.]]
Sea otters are [[polygynous]]: males have multiple female partners. However, temporary pair-bonding occurs for a few days between a female in [[estrus]] and her mate.<ref name=wp/> Mating takes place in the water and can be rough, the male biting the female on the muzzle – which often leaves scars on the nose – and sometimes holding her head under water.<ref name=adw/><ref>At least one female is known to have died from an infected nose. (Love, p. 52)</ref>
Births occur year-round, with peaks between May and June in northern populations and between January and March in southern populations.<ref name=love54>Love, p. 54</ref> [[Gestation]] appears to vary from four to twelve months, as the species is capable of [[delayed implantation]] followed by four months of pregnancy.<ref name=love54>Love, p. 54</ref> In California, sea otters usually breed every year, about twice as often as sea otters in Alaska.<ref>Silverstein, p. 30</ref>
Birth usually takes place in the water and typically produces a single pup weighing 1.4 to 2.3 kg (3 to 5 lb).<ref name = Nowak/> Twins occur in 2% of births; however, usually only one pup survives.<ref name=adw/> At birth, the eyes are open, ten teeth are visible, and the pup has a thick coat of baby fur.<ref>Kenyon, p.44</ref> Mothers have been observed to lick and fluff a newborn for hours; after grooming, the pup's fur retains so much air that the pup floats like a cork and cannot dive.<ref>Love, pp. 56–61</ref> The fluffy baby fur is replaced by adult fur after about thirteen weeks.<ref name=wdfw/>
[[Image:Sea-otter-bay 11.jpg|thumb|left|250px|A mother floats with her pup on her chest. [[Georg Steller]] wrote, "They embrace their young with an affection that is scarcely credible."<ref name=love58>Love, p. 58</ref>]]
[[Lactation|Nursing]] lasts six to eight months in California populations and four to twelve months in Alaska, with the mother beginning to offer bits of prey at one to two months.<ref>Silverstein, pp. 31–32</ref> The milk from a sea otter's two abdominal [[nipple]]s is rich in fat and more similar to the milk of other marine mammals than to that of other [[mustelid]]s.<ref>Love, p. 61</ref> 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.<ref name=haley/> Juveniles are typically independent at six to eight months, however a mother may be forced to abandon a pup if she cannot find enough food for it<ref name=love63>Love, p. 63</ref> and at the other extreme, a pup may nurse until it is almost adult size.<ref name=Nowak/> Pup mortality is high, particularly during an individual's first winter – by one estimate, only 25% of pups survive their first year.<ref name=love63>Love, p.63</ref> Pups born to experienced mothers have the highest survival rates.<ref>Love, p. 62</ref>
Females perform all tasks of feeding and raising offspring, and have occasionally been observed caring for orphaned pups.<ref>Love, p. 59</ref> 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.<ref>Kenyon, p. 89</ref> When foraging, she leaves her pup floating on the water, sometimes wrapped in kelp to keep it from floating away;<ref>Silverstein, p. 31</ref> if the pup is not sleeping, it cries loudly until she returns.<ref>Silverstein, p. 28</ref> Mothers have been known to carry their pup for days after the pup's death.<ref name=love58>Love, p. 58</ref>
Females become sexually mature at around three or four years of age and males at around five; however, males often do not successfully breed until a few years later.<ref name=love53>Love, p. 53</ref> A captive male sired offspring at age 19.<ref name=Nowak>{{cite book|title=Walker's Mammals of the World Volume II|Edition=Fifth|author=Nowak, Roland M. |publisher=The John Hopkins University Press|location=Baltimore and London|year=1991|isbn=0-8018-3970-X|pages=1141–1143}}</ref> In the wild, sea otters live to a maximum age of 23 years,<ref name=marinebio/> with average lifespans of 10–15 years for males and 15–20 years for females.<ref>VanBlaricom, p. 71</ref> Several captive individuals have lived past 20 years, and a female at the [[Seattle Aquarium]] died at the age of 28 years.<ref>VanBlaricom, pp. 40–41</ref> Sea otters in the wild often develop worn [[teeth]], which may account for their apparently shorter lifespans.<ref>VanBlaricom, p. 41</ref>
==Population and distribution==
{{seealso|Sea otter conservation}}
[[Image:Sea otters at moss landing.jpg|thumb|right|220px|A raft of sea otters in [[Moss Landing, California]].]]
Sea otters live in coastal waters 15 to 23 meters (50 to 75 ft) deep,<ref name=silverstein17>Silverstein, p. 17</ref> and usually stay within a kilometer (⅔ mi) 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> Although they are most strongly associated with rocky [[substrate (marine biology)|substrate]]s, sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt.<ref>VanBlaricom, p. 14</ref> Their northern range is limited by ice, as sea otters can survive amidst [[drift ice]] but not [[land-fast ice]].<ref>Kenyon, p. 133</ref> Individuals generally occupy a home range a few kilometers long, and remain there year-round.<ref name=love6769>Love, pp. 67–69</ref>
The sea otter population is thought to have once been 150,000 to 300,000,<ref name=silverstein34>Silverstein, p. 34</ref> stretching in an arc across the North Pacific from northern Japan to the central [[Baja Peninsula]] in Mexico. The fur trade that began in the 1740s reduced the sea otter's numbers to an estimated 1,000 to 2,000 members in thirteen colonies. In about two-thirds of its former range, the species is at varying levels of recovery, with high population densities in some areas and [[threatened species|threatened]] populations in others. Sea otters currently have stable populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, and there have been reports of recolonizations in Mexico and Japan.<ref>VanBlaricom, p. 54</ref> Population estimates made between 2004 and 2007 give a worldwide total of approximately 107,000 sea otters.<ref name=Kornev/><ref name=alaskafws/><ref name=bc/><ref name=wdfw/><ref name=Leff/>
===Russia===
Currently, the most stable and secure part of the sea otter's range is [[Russia]].<ref name=vb62/> 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.<ref name=Kornev/> 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.<ref name=Kornev/> Growth has slowed slightly, suggesting that the numbers are reaching [[carrying capacity]].<ref name=Kornev>Kornev S.I., Korneva S.M. (2004) [http://2mn.org/downloads/bookshelf/mm3_book/254-307.pdf 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.</ref>
===Alaska===
[[Alaska]] is the heartland of the sea otter's range. In 1973, the sea otter population in Alaska was estimated at between 100,000 and 125,000 animals.<ref>Nickerson, p. 46</ref> By 2006, however, the Alaska population had fallen to an estimated 73,000 animals.<ref name=alaskafws>
{{cite web|url=http://alaska.fws.gov/fisheries/mmm/seaotters/recovery.htm|title=Sea Otters – Southwest Alaska Sea Otter Recovery Team (SWAKSORT)|publisher=U.S. Fish and Wildlife Service – Alaska|accessdate=2008-01-15}}</ref> A massive decline in sea otter populations in the [[Aleutian Islands]] accounts for most of the change; the cause of this decline is not known, although [[orca]] predation is suspected.<ref name=Schrope/> The sea otter population in [[Prince William Sound]] was also hit hard by the [[Exxon Valdez oil spill]], which killed thousands of sea otters in 1989.<ref name=wp/>
===British Columbia and Washington===
Along the North American coast south of Alaska, the sea otter's range is discontinuous. 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 Provincial Park|Cape Scott]].<ref name=bc/> In 1989, a separate colony was discovered in the central British Columbia 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.<ref name=bc>{{cite web|url=http://www.vanaqua.org/aquanew/fullnews.php?id=1692|title=British Columbia: Sea Otter Research Expedition|publisher=Vancouver Aquarium|author=Barrett-Lennard, Lance|date=20 October 2004|accessdate=2007-12-11}}</ref>
In 1969 and 1970, 59 sea otters were translocated from Amchitka Island to [[Washington State]]. Annual surveys between 2000 and 2004 have recorded between 504 and 743 individuals, and their range is in the [[Olympic Peninsula]] from just south of Destruction Island to Pillar Point.<ref name=wdfw>{{cite web|url=http://wdfw.wa.gov/wlm/diversty/soc/recovery/seaotter/index.htm|title=
Final Washington State Sea Otter Recovery Plan|publisher=Washington Department of Fish and Wildlife|accessdate=2007-11-29}}</ref>
[[Image:Sea-otter-with-pup-morro-rock.jpg|thumb|left|California has over 3,000 sea otters, descendants of approximately 50 individuals discovered in 1938.]]
In British Columbia and Washington, sea otters are found almost exclusively on the outer coasts. Reported sightings of sea otters in the [[San Juan Islands]] and [[Puget Sound]] almost always turn out to be [[northern river otter]]s which are commonly seen along the seashore. However, biologists have confirmed isolated sightings of sea otters in these areas since the mid-1990s.<ref name=wdfw/>
===California===
The spring 2007 sea otter survey counted 3,026 sea otters in the central California coast, down from an estimated pre-fur trade population of 16,000.<ref name=Leff>{{cite news|title=California otters rebound, but remain at risk|url=http://www.mailtribune.com/apps/pbcs.dll/article?AID=/20070615/LIFE/706150317|date=15 June 2007|author=Leff, Lisa|publisher=Associated Press|accessdate=2007-12-25}}</ref><ref name=ca07>{{cite web |url=http://www.werc.usgs.gov/otters/ca-surveyspr2007.htm|title=Spring 2007 Mainland California Sea Otter Survey Results|publisher=U.S. Geological Survey|date= 30 May 2007|accessdate=2008-02-23}}</ref> California's sea otters are the descendants of a single colony of about 50 southern sea otters discovered near [[Big Sur]] in 1938;<ref>Silverstein, p. 41</ref> their principal range is now from just south of [[San Francisco]] to [[Santa Barbara County]].<ref name=ca07/> In the late 1980s, the [[U.S. Fish and Wildlife Service]] relocated about 140 California sea otters to [[San Nicolas Island]] in southern California, in the hope of establishing a reserve population should the mainland be struck by an oil spill. To the surprise of biologists, the San Nicholas population initially shrank as the animals migrated back to the mainland,<ref name=santacruz/> As of 2005, only 30 sea otters remained at San Nicholas,<ref name=fws/> thriving on the abundant prey around the island.<ref name=santacruz/> The plan that authorized the translocation program had predicted that carrying capacity would be reached within 5 to 10 years.
When the Fish and Wildlife Service implemented the translocation program, it also attempted to implement "zonal management" of the California population. To manage the competition between sea otters and fisheries, it declared an "otter-free zone" stretching from [[Point Conception]] to the Mexican border. In this zone, only San Nicolas Island was designated as sea otter habitat, and sea otters found elsewhere in the area were supposed to be captured and relocated. These plans were abandoned after it proved impractical to capture the hundreds of otters which ignored regulations and swam into the zone.<ref name=cnn>{{cite news|title=Balance sought in sea otter conflict|url=http://www.cnn.com/NATURE/9903/24/otters.enn/|date=March 24, 1999|accessdate=2008-01-25|publisher=CNN}}</ref> However, after engaging in a period of public commentary in 2005, the Fish and Wildlife Service has yet to release a formal decision on the issue.<ref name=fws>{{cite web|url=http://www.fws.gov/pacific/news/2005/seaotterNR.pdf|title=U.S. Fish and Wildlife Service Proposes that Southern Sea Otter Translocation Program be Terminated |publisher=U.S. Fish and Wildlife Service |date=5 October 2005|accessdate=2008-04-10}}</ref>{{-}}
==Ecology==
===Diet===
[[Image:Kelp-forest-Monterey.jpg|thumb|right|150px|Sea otters keep [[kelp forest]]s healthy by eating animals that graze on kelp.]]
Sea otters consume over 100 different prey species.<ref name=v1829/> In most of its range, the sea otter's diet consists almost exclusively of marine invertebrates, including [[sea urchin]]s, a variety of [[bivalve]]s such as [[clam]]s and [[mussel]]s, [[abalone]], other [[mollusk]]s, [[crustacean]]s, and [[snail]]s.<ref name=v1829/> Its prey ranges in size from tiny [[limpet]]s [[crab]]s to [[giant octopus]]es.<ref name=v1829>VanBlaricom pp. 18–29</ref> Where prey such as sea urchins, clams, and abalone are present in a range of sizes, sea otters tend to select larger items over smaller ones of similar type.<ref name=v1829/> In California, it has been noted that sea otters ignore [[Pismo clam]]s smaller than 3 inches (7 cm) across.<ref>Love, p. 96</ref>
In a few northern areas, fish are also eaten. In studies performed at [[Amchitka Island]] in the 1960s, where the sea otter population was at [[carrying capacity]], 50% of food found in sea otter stomachs was fish.<ref name=kenyon121>Kenyon, p. 121</ref> The fish species were usually bottom-dwelling and sedentary or sluggish forms, such as the [[red Irish lord]] and [[globefish]].<ref name=kenyon121/> However, south of Alaska on the North American coast, fish are a negligible or extremely minor part of the sea otter's diet.<ref>Love, p. 76</ref><ref name=wdfw/> Contrary to popular depictions, sea otters rarely eat [[starfish]], and any [[kelp]] that is consumed apparently passes through the sea otter's system undigested.<ref name=kenyon119>Kenyon, p. 119</ref>
The individuals within a particular area often differ in their foraging methods and their prey types, and tend to follow the same patterns as their mothers.<ref>VanBlaricom, p. 29</ref> The diet of local populations also changes over time, as sea otters can significantly deplete populations of highly preferred prey such as large sea urchins, and prey availability is also affected by other factors such as fishing by humans.<ref name=wdfw/> Sea otters can thoroughly remove abalone from an area except for specimens in deep rock crevices,<ref>VanBlaricom, p. 30</ref> however, they never completely wipe out a prey species from an area.<ref>Nickerson, p. 57</ref> A 2007 California study demonstrated that in areas where food was relatively scarce, a wider variety of prey was consumed. However, surprisingly, the diets of individuals were more specialized in these areas than in areas where food was plentiful.<ref name=santacruz>{{cite web|url=http://www.sciencedaily.com/releases/2008/01/080114173901.htm|title=Sea Otter Show Striking Variability In Diets And Feeding Strategies|author=University of California — Santa Cruz|publisher=ScienceDaily|date=18 January 2008|accessdate=2008-01-20}}</ref>
===As a keystone species===
Sea otters are a classic example of a [[keystone species]]; their presence affects the ecosystem more profoundly than their size and numbers would suggest. Sea otters keep the population of certain [[benthic]] (sea floor) herbivores, particularly [[sea urchin]]s, 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/>
[[Image:CalifCentralCoast.jpg|thumb|left|Remote areas of coastline, such as this area in California, sheltered the few remaining colonies of sea otters that survived the fur trade.]]
Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems,<ref name=dfo>{{cite web|url=http://www.dfo-mpo.gc.ca/species-especes/species/species_seaOtter_e.asp|title=Aquatic Species at Risk – Species Profile – Sea Otter|publisher=[[Fisheries and Oceans Canada]]|accessdate=2007-11-29}}</ref> and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the [[Big Sur]] coast of California<ref name=vanblaricom33>VanBlaricom, p. 33</ref> However, some kelp forest [[ecosystem]]s in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors.<ref name=vanblaricom33>VanBlaricom, p. 33</ref> 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]].<ref name=vanblaricom33>VanBlaricom, p. 33</ref>
In addition to promoting growth of kelp forests, sea otters can also have a profound effect in rocky areas that tend to be dominated by [[mussel]] beds. They remove mussels from rocks, liberating space for competitive species and thereby increasing the diversity of species in the area.<ref>VanBlaricom, p. 33</ref>
===Predators===
Predators of sea otters include [[orca]]s and [[sea lion]]s; [[bald eagle]]s also prey on pups by snatching them from the water surface.<ref name=vanaqua/>
In California, bites from [[shark]]s, particularly [[great white shark]]s, have been estimated to cause 10% of sea otter deaths and are one of the reasons the population has not expanded further north.<ref name = Nickerson65/> Dead sea otters have been found with injuries from shark bites, although there is no evidence that sharks actually eat them.<ref name = Nickerson65>Nickerson, p. 65</ref>
==Relationship with humans==
===Fur trade===
[[Image:Sea otter hunters 1896.jpg|thumb|right|200px|[[Aleut]] men in [[Unalaska]] in 1896. The waterproof [[kayak]] gear and garments were used to hunt sea otters.]]
Archaeological evidence indicates that for thousands of years, [[indigenous peoples]] have hunted sea otters in moderation for food and fur.<ref name=silverstein34>Silverstein, p. 34</ref> Large-scale hunting, which would eventually kill approximately one million sea otters, 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.<ref name=silverstein34>Silverstein, p. 34</ref>
In the early 1700s, Russians began to hunt sea otters in the [[Kuril Islands]] and sold them to [[China]].<ref name=silverstein34>Silverstein, p. 34</ref> 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.<ref name=silverstein35>Silverstein, p. 35</ref> 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.<ref name=silverstein35>Silverstein, p. 35</ref> 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.<ref name=silverstein35>Silverstein, p. 35</ref> They returned to Siberia having killed nearly 1000 sea otters, and were able to command high prices for the pelts.<ref name=silverstein35>Silverstein, p. 35</ref> Thus began what is sometimes called the "Great Hunt", which would continue for another hundred years.
[[Image:London Sea Otter pelt sales 1871-1910.svg|thumb|left|Pelt sales (in thousands) in the London fur market. The drop beginning in the 1880s reflects dwindling sea otter populations.<ref name=Brass>Brass E. (1911) ''Aus dem Reiche der Pelze, Bd III'', Berlin</ref>]]
Russian fur-hunting expeditions soon depleted the sea otter populations in the Commander Islands, and by 1745 they began to move on to the [[Aleutian Islands]]. The Russians initially traded with the [[Aleut]]s inhabitants of these islands 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.<ref name=silverstein37>Silverstein, p. 37</ref> The Aleut population was reduced, by the Russians' own estimate, from 20,000 to 2,000.<ref name=Gedney>{{cite web|url=http://www.gi.alaska.edu/ScienceForum/ASF6/605.html|title=The Aleut and the Otter|author=Gedney, Larry|date=6 May 1983|accessdate=2008-02-23}}</ref> 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]], [[Spain|Spanish]] explorers bought sea otter pelts from [[Indigenous peoples of the Americas|Native Americans]] and sold them in Asia.<ref name=silverstein37>Silverstein, p. 37</ref> In 1778, British explorer [[Captain James Cook]] reached [[Vancouver Island]] and bought sea otter furs from the First Nations people.<ref name=silverstein38>Silverstein, p. 38</ref> When Cook's ship later stopped at a [[China|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.<ref name=silverstein38>Silverstein, p. 38</ref>
Russian hunting expanded to the south, in what is now Washington, Oregon, and California, and the Russians founded what is now the [[Fort Ross, California|Fort Ross]] settlement in northern California as their southern headquarters.<ref name=silverstein38>Silverstein, p. 38</ref> In the next 29 years, they would kill 50,000 California sea otters.<ref name=silverstein38>Silverstein, p. 38</ref>
Eventually, sea otter populations became so depleted that commercial hunting was no longer viable. In the Aleutian Islands, commercial hunting had stopped by 1808.<ref name=silverstein40>Silverstein, p. 40</ref> When Russia [[Alaska purchase|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.<ref name=silverstein40>Silverstein, p. 40</ref> Prices rose as the species became rare: During the 1880s, a pelt brought $105 to $165 in the London market, however by 1903 a pelt could be worth as much as $1,125.<ref name=Nowak/> 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.<ref>VanBlaricom, p. 50</ref> So few remained, perhaps only 1,000–2,000 individuals in the wild, that many believed the species would become [[extinction|extinct]].<ref name=wdfw/>
===Recovery and conservation===
{{Main|Sea otter conservation}}
[[Image:OilSheenFromValdezSpill.jpeg|thumb|right|In the wake of the [[Exxon Valdez oil spill]], heavy sheens of oil covered large areas of [[Prince William Sound]].]]
During the 20th century, sea otter numbers rebounded in about two-thirds of their historic range, a recovery that is considered one of the greatest successes in marine conservation.<ref>VanBlaricom, p. 53</ref> However, the [[IUCN]] lists the sea otter as an [[endangered species]], and describes the significant threats to sea otters as [[oil pollution]], predation by [[orca]]s, [[poaching]], and conflicts with fisheries – sea otters can drown if entangled in fishing gear.<ref name=IUCN>{{IUCN2006|assessors=Estes|year=2000|id=7750|title=Enhydra lutris|downloaded=11 May 2006}}</ref> The hunting of sea otters is no longer legal except for limited harvests by [[indigenous peoples]] in the United States.<ref>VanBlaricom, p. 65</ref> Poaching was a serious concern in the Russian Far East immediately after the [[History of the Soviet Union (1985–1991)|collapse of the Soviet Union]] in 1991, however it has declined significantly with stricter law enforcement and better economic conditions.<ref name=vb62>VanBlaricom, p. 62</ref>
The most significant threat to sea otters is [[oil spill]]s.<ref name=vanaqua>{{cite web|title=Sea otter AquaFact file|url=http://www.vanaqua.org/education/aquafacts/seaotters.html|publisher = [[Vancouver Aquarium Marine Science Centre]]|accessdate=2007-12-05}}</ref> 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]].<ref name=vanaqua/> The [[liver]], [[kidney]]s, and [[lung]]s of sea otters also become damaged after they inhale oil or ingest it when grooming.<ref name=vanaqua/> The [[Exxon Valdez oil spill]] of 24 March 1989 killed thousands of sea otters in [[Prince William Sound]], and as of 2006 the lingering oil in the area continues to affect the population.<ref>{{cite news|url=http://www.usatoday.com/news/nation/2007-01-31-exxon-alaska_x.htm|title=Damage of Exxon Valdez endures|publisher=Associated Press|date=31 January 2007|accessdate=2001-12-25}}</ref> Describing the public sympathy for sea otters that developed from media coverage of the event, a U.S. Fish and Wildlife Service spokesperson wrote:
{{quote|As a playful, photogenic, innocent bystander, the sea otter epitomized the role of victim ... cute and frolicsome sea otters suddenly in distress, oiled, frightened, and dying, in a losing battle with the oil.<ref name=wdfw/>
}}
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.<ref name=wp/><ref name=wlap/><ref name=wdfw/> Prevention of oil spills and preparation for the rescue of otters in the event of one are major areas of focus for conservation efforts. Increasing the size and the range of sea otter populations would also reduce the risk of an oil spill wiping out a population.<ref name=wdfw/> However, because of the species' reputation for depleting shellfish resources, advocates for commercial, recreational, and subsistence shellfish harvesting have often opposed allowing the sea otter's range to increase, and there have even been instances of fishermen and others illegally killing them.<ref>Nickerson, pp. 47–48</ref>
[[Image:Sea otter pair2.jpg|thumb|left|200px|Sea otters in the [[Olympic Coast National Marine Sanctuary]]. Note the unusual shape of the hind feet, in which the outer toes are longest.]]
In the Aleutian Islands, a massive and unexpected disappearance of sea otters has occurred in recent decades. 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.<ref name=cnn>{{cite web|url=http://archives.cnn.com/2000/NATURE/07/06/otter.survey.enn/index.html|title=Aleutian Sea Otter population falls 70% in eight years|date=6 July 2000|accessdate=2007-12-04|publisher=CNN}}</ref> The most widely-accepted, but still controversial, hypothesis is that [[orcas]] have been eating the otters. The pattern of sea otter disappearances is consistent with a rise in orca predation, however there has been no direct evidence that orcas prey on sea otters to any significant extent.<ref name=Schrope>{{cite journal|url=http://naturereprints.com/nature/journal/v445/n7129/full/445703a.html|title=Food chains: Killer in the kelp|journal=Nature|author=Schrope, Mark|volume=445|pages= 703–705 |date=15 February 2007|doi=10.1038/445703a}}</ref>
Another area of concern is California, where recovery began to fluctuate or decline in the late 1990s.<ref name=ASLC>{{cite web|title=Sea Otters: Species Description|publisher=Alaska SeaLife Center|url=http://www.alaskasealife.org/New/research/index.php?page=seaotter_research.php|accessdate=2007-01-15}}</ref> Unusually high mortality rates amongst adult and sub-adult otters, particularly females, have been reported.<ref name=Leff>{{cite news|title=California otters rebound, but remain at risk|url=http://www.mailtribune.com/apps/pbcs.dll/article?AID=/20070615/LIFE/706150317|date=15 June 2007|author=Leff, Lisa|publisher=Associated Press|accessdate=2007-12-25}}</ref> [[Necropsies]] of dead sea otters indicate that diseases, particularly ''[[Toxoplasma gondii]]'' infection and [[acanthocephala]]n parasite infection, are a major cause of sea otter mortality in California.<ref name=kreuder>{{cite journal |journal=Journal of Wildlife Diseases|volume= 39|number=3|year=2003|pages= 495–509|title=Patterns of Mortality in Southern Sea Otters (Enhydra Lutris Nereis) from 1998 - 2001|author=Kreuder, C. et al}}</ref> The ''Toxoplasma gondii'' parasite, which is often fatal to sea otters, is carried by wild and domestic cats and by [[opossum]]s, and may be transmitted by domestic cat droppings flushed into the ocean via the sewage system.<ref name=kreuder/><ref name=mag72>{{cite news|url=http://www.magazine.noaa.gov/stories/mag72.htm|title=Parasite in cats killing sea otters|publisher=[[National Oceanic and Atmospheric Administration]]|date=21 January 2003|work=NOAA magazine|accessdate=2007-11-24}}</ref> Although it is clear that disease has contributed to the deaths of many of California's sea otters, it is not known why the California population is apparently more affected by disease than populations in other areas.<ref name=kreuder/>
Sea otter habitat is preserved through several [[Marine protected area|protected areas]] in the [[Protected areas of the United States|United States]], [[Protected areas in Russia|Russia]] and [[Protected areas of Canada|Canada]]. In marine protected areas, polluting activities such as dumping of waste and oil drilling are typically prohibited.<ref>{{cite web |title=National Marine Sanctuaries Regulations| publisher = [[NOAA]] |url=http://sanctuaries.noaa.gov/protect/regulations/welcome.html|accessdate=2008-03-19}}</ref> There are estimated to be more than 1,200 sea otters within the [[Monterey Bay National Marine Sanctuary]], and more than 500 within the [[Olympic Coast National Marine Sanctuary]].<ref>{{cite web |title=Monterey Bay National Marine Sanctuary |publisher = City of Monterey|url=http://www.monterey.org/harbor/mbnms.html|accessdate=2008-03-19}}</ref> <ref>{{cite web |title=Olympic Coast National Marine Sanctuary History|publisher=[[NOAA]] |url=http://olympiccoast.noaa.gov/living/history_and_culture/history/welcome.html|accessdate=2008-03-19}}</ref>
===Economic impact===
[[Image:Sea Otteruses a rock to break a shell open 2.jpg|A sea otter using a rock to break open a shell|thumb|right]]
Some of the sea otter's preferred prey species, particularly [[abalone]], [[clam]]s, and [[crab]]s, are also food sources for humans. In some areas, massive declines in [[shellfish]] harvests have been blamed on the sea otter, and intense public debate has taken place over how to manage the competition between sea otters and humans for seafood.<ref name=vb34/>
The debate is complicated by the fact that sea otters have sometimes been held responsible for declines of shellfish stocks that were more likely caused by [[overfishing]] by humans, disease, pollution, and [[seismic]] activity.<ref name=Love9398>Love, pp. 93–98</ref><ref name=wp/> Shellfish declines have also occurred in many parts of the North American Pacific coast that do not have sea otters, and conservationists sometimes note that the existence of large concentrations of shellfish on the coast is a recent development resulting from the fur trade's near-[[extirpation]] of the sea otter.<ref name=Love9398/> Although many factors affect shellfish stocks, sea otter predation can deplete a fishery to the point that it is no longer commercially viable.<ref name=vb34/> There is a consensus among scientists that sea otters and abalone fisheries cannot co-exist in the same area,<ref name=vb34>VanBlaricom, p. 34</ref> and the same is likely true for certain other types of shellfish as well.<ref name=cnn/>
There are many facets to the interaction between sea otters and the human economy that are not as immediately felt. Sea otters have been credited with contributing to the [[kelp]] harvesting industry via their well-known role in controlling sea urchin populations; kelp is used in the production of diverse food and pharmaceutical products.<ref name = Silverstein49>Silverstein, p. 49</ref> Although human divers harvest [[red sea urchin]]s both for food and to protect the kelp, sea otters hunt more sea urchin species and are more consistently effective in controlling these populations.<ref>Nickerson, p. 70</ref> The health of the kelp forest ecosystem is significant in nurturing populations of fish, including commercially important fish species.<ref name=Silverstein49/> In some areas, sea otters are a popular [[tourism|tourist]] attraction, bringing visitors to local hotels, restaurants, and sea otter-watching expeditions.<ref name=Silverstein49/>
===Role in human cultures===
{|class="graytable" style="text-align:left"
<span class="subcaption"> </span>
|width="20%"|[[Image:AleutKalan1.jpg|center|60px]]
|width="80%"|[[Image:AleutKalan2.jpg|center|600px|Aleut carving of a sea otter hunt]]
<small> '''Left''': [[Aleut]] sea otter [[amulet]] in the form of a mother with pup. '''Above''': Aleut carving of a sea otter hunt on a whalebone spear. Both items are on display at the [[St. Petersburg]] [[Peter the Great Museum of Anthropology and Ethnography|Museum of Anthropology and Ethnography]]. Articles depicting sea otters were considered to have magical properties.<ref name="Lyapunova1963">''Lyapunova R.G.'' (1963) Museum materials on the Aleuts. Catalog of the Museum of anthropology and ethnography. Academy of Sciences, USSR, vol. XXI.</ref> </small>
|}
For many maritime indigenous cultures throughout the North Pacific, especially the [[Ainu people|Ainu]] in the Kuril Islands, the [[Koryaks]] and [[Itelmen]] of Kamchatka, the [[Aleut]] in the Aleutian Islands and a host of [[Indigenous peoples of the Pacific Northwest Coast|tribes on the Pacific coast of North America]], the sea otter has played an important role as a cultural as well as material resource. In these cultures, many of which have strongly [[animist]] traditions full of legends and stories in which many aspects of the natural world are associated with spirits, the sea otter was considered particularly kin to humans. The [[Nuu-chah-nulth]], [[Haida]], and other [[First Nations]] of coastal British Columbia used the warm and luxurious pelts as chiefs' regalia. Sea otter pelts were given in [[potlatch]]es to mark coming-of-age ceremonies, weddings, and funerals.<ref name=tyee1>{{cite web|url=http://thetyee.ca/News/2007/10/04/SeaOtter1/|title=Too Many Sea Otters?|author= Okerlund, Lana|date=4 October 2007|accessdate=2007-01-15}}</ref> The Aleuts carved sea otter bones for use as ornaments and in games, and used powdered sea otter [[baculum]] as a medicine for fever.<ref name=Love3435>Love, pp 34–35</ref>
[[Image:Sea otters Lisbon.JPG|thumb|220px|right|Sea otters at the [[Lisbon Oceanarium]] show their flexibility when grooming.]]
Among the Ainu, the otter is portrayed as an occasional messenger between humans and the creator.<ref name=Basil>{{ Citation | last=Chamberlain | first=B. | title=Aino Folk Tales | publisher=The folk-lore society, private printing | place=London, | year=1888 | url = http://www.sacred-texts.com/shi/aft/aft.htm#vi }} </ref> Versions of a widespread Aleut legend tell of lovers or despairing women who plunge into the sea and become otters.<ref> F. A. Golder. (1905) Aleutian Stories. ''The Journal of American Folklore'', Vol. 18, No. 70. (July–September), pp. 215–222.</ref> These links have been associated with the many human-like behavioral features of the sea otter, including apparent playfulness, strong mother-pup bonds and tool use, yielding to ready [[anthropomorphism]].<ref name="Barabash1947">''N. I. Barabash-Nikiforov'' (1947) Калан (''Enhydra lutris L.'') его биология и вопросы хозяйства (The sea otter (''Engydra lutris L''): biology and management), Published by: Natural Preservation Ministry of the RSFSR, Moscow.</ref> The beginning of commercial exploitation had a great impact on the human as well as animal populations – the Ainu and Aleuts have been displaced or their numbers are dwindling, while the coastal tribes of North America, where the otter is in any case greatly depleted, no longer rely as intimately on sea mammals for survival.<ref>Hatch, David R. (2002) Elakha: Sea Otters, Native People, and European Colonization in the North Pacific. In ''Changing Landscapes: Proceedings of the 5th and 6th Annual Coquille Cultural Preservation Conferences.'' Donald B. Ivy and R. Scott Byram, eds. Pp. 79–88. North Bend, OR: Coquille Indian Tribe.</ref>
Since the mid-1970s, the beauty and charisma of the species have gained wide appreciation, and the sea otter has become an icon of environmental conservation.<ref name=ASLC>{{cite web|title=Sea Otters: Species Description|publisher=Alaska SeaLife Center|url=http://www.alaskasealife.org/New/research/index.php?page=seaotter_research.php|accessdate=2007-01-15}}</ref> The round, expressive face and soft furry body of the sea otter are depicted in a wide variety of souvenirs, postcards, clothing, and stuffed toys.<ref name=love97>Love, p. 97</ref>
===Aquariums and zoos===
Sea otters can do well in [[Captivity (animal)|captivity]], and are featured in over 40 public [[aquarium]]s and [[zoo]]s.<ref>VanBlaricom p. 69</ref> The [[Seattle Aquarium]] became the first institution to raise sea otters from conception to adulthood with the birth of Tichuk in 1979, followed by three more pups in the early 1980s.<ref>{{cite news
|title=Seattle Aquarium's Youngest Sea Otter Lootas Becomes a Mom
|date=April 19 2000
|publisher= Business Wire
|accessdate=2007-03-09
|url=http://www.allbusiness.com/transportation/marine-transportation-marine-accidents/6425408-1.html}}</ref> In 2007, a [[YouTube]] video of two sea otters holding paws drew 1.5 million viewers in two weeks, and currently has over 10.5 million views.<ref>{{cite web
|title=Otters holding hands
|url=http://www.youtube.com/watch?v=epUk3T2Kfno
|author=cynthiaholmes
|date=2007-03-19
|publisher=YouTube
|accessdate=2008-03-24}}</ref> Filmed five years previously at the [[Vancouver Aquarium]], it was YouTube's most popular animal video at the time, although it has since been surpassed. The lighter-colored otter in the video is Nyac, a survivor of the 1989 [[Exxon Valdez oil spill|''Exxon Valdez'' oil spill]].<ref name=Nyac>{{cite web
|title= Vancouver sea otters a hit on YouTube
|date=3 April 2007
|publisher= CBC News
|accessdate=2007-01-15
|url=http://www.cbc.ca/canada/british-columbia/story/2007/04/03/bc-youtube.html}}</ref>
==Notes==
{{reflist|2}}
==References==
<!-- An alphabetical listing of inline citations (previous section) should be listed here. -->
* {{cite book | title=The Sea Otter in the Eastern Pacific Ocean | last=Kenyon |first=Karl W.|
year=1969|publisher=U.S. Bureau of Sport Fisheries and Wildlife|location=Washington, D.C.}}
* {{cite book |title= Sea Otters|last= Love|first=John A. |authorlink= |coauthors= |year= 1992|publisher=Fulcrum Publishing|location=Golden, Colorado |isbn=1-55591-123-4}}
* {{cite book | title= Sea Otters, a Natural History and Guide | last=Nickerson |first=Roy|
year=1989|publisher=Chronicle Books|location=San Francisco, CA|isbn=0-87701-567-8}}
* {{cite book |title= The Sea Otter|last= Silverstein |first= Alvin|authorlink= |coauthors= Silverstein, Virginia and Robert|year= 1995|publisher= The Millbrook Press, Inc. |location= Brookfield, Connecticut|isbn=1-56294-418-5}}
* {{cite book | title=Sea Otters|year=2001|last=VanBlaricom|first=Glenn R.|publisher=Voyageur Press Inc.|location=Stillwater, MN|isbn=0-89658-562-X}}
==External links==
{{Portal|Marine life|Yellow.tang.arp.jpg}}
{{Portal|Mammals|Dwarf_mongoose_Korkeasaari_zoo.jpg}}
{{Commons|Enhydra lutris}}
{{Wikispecies|Enhydra lutris}}
* [http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1019&context=libraryscience Field notes by Georg Wilhelm Steller, 1742] (PDF)
* [http://www.montereybayaquarium.org/efc/efc_otter/otter_cam.asp Live sea otter webcam – Monterey Bay Aquarium]
* [http://www.vanaqua.org/ottercam/ Live sea otter webcam – Vancouver Aquarium]
* [http://www.youtube.com/watch?v=epUk3T2Kfno Otters holding hands] – The popular YouTube video
* [http://online.wr.usgs.gov/outreach/otter/ Precipice of Survival: The Southern Sea Otter] (video)
* [http://www.otterproject.org The Otter Project] – Organization for protecting the California sea otter
* [http://seaotters.org Friends of the Sea Otter]
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