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{{Short description|Species of marine mammal (Enhydra lutris)}}
{{Hatnote group|{{Distinguish|text=the [[marine otter]] or [[Eurasian otter]]}}{{other uses}}}}
{{Featured article}}
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{{Use dmy dates|date=August 2022}}
{{Speciesbox
 | name              = Sea otter
 | status            = EN
 | status_system     = IUCN3.1
 | status_ref        =<ref name="iucn status 23 May 2025">{{cite iucn |author=Doroff, A. |author2=Burdin, A. |date=2020 |title=''Enhydra lutris'' |volume=2021 |page=e.T7750A219377647 |doi=10.2305/IUCN.UK.2021-3.RLTS.T7750A219377647.en |access-date=23 May 2025}}</ref>
 | status2 = CITES_A2 
 | status2_system = CITES 
 | status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>{{NoteTag|''Enhydra lutris nereis'' is included in Appendix I}}
 | image             = Sea Otter (Enhydra lutris) (25169790524) crop.jpg
 | image_caption     = In [[Morro Bay, California]]
 | genus             = Enhydra
 | species           = lutris
 | authority         = ([[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]])
| subdivision_ranks = Subspecies
| subdivision = :''E. l. lutris''
:''E. l. kenyoni''
:''E. l. nereis''
 | display_parents   = 2
 | range_map         = Sea otter distribution.svg
 | range_map_caption = Sea otter range
 | synonyms          = *''Mustela lutris'' <small>Linnaeus,&nbsp;1758</small>
}}                         

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 [[otter]]s typically weigh between {{convert|14|and|45|kg|abbr=on|sigfig=1}}, making them the heaviest members of the [[Mustelidae|weasel family]], but among<ref>{{Cite web |title=The secret life of otters |url=https://www.montereybayaquarium.org/animals/animals-a-to-z/sea-otter |access-date=2023-10-02 |website=www.montereybayaquarium.org}}</ref> 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 dives to the sea floor to [[Foraging|forage]]. It preys mostly on marine [[Invertebrate|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. Its [[Tool use by sea otters|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]] [[ecosystem]]s.<ref name="Womble-2016">{{Cite web|last=Womble|first=Jamie|date=2016-07-29|title=A Keystone Species, the Sea Otter, Colonizes Glacier Bay|url=https://www.nps.gov/glba/blogs/a-keystone-species-the-sea-otter-colonizes-glacier-bay.htm |access-date=2021-11-23|website=National Park Service |language=en}}</ref> 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 living in a fraction of their historic range.<ref name= Riedman>{{cite report |title=The sea otter (''Enhydra lutris''): behavior, ecology, and natural history |author1=Riedman, M.L. |author2=Estes, James A. |author-link2=James A. Estes |journal=U.S. Fish and Wildlife Service Biological Report |year=1990 |page=126 |location=Washington, D.C. |url=http://www.fort.usgs.gov/Products/Publications/pub_abstract.asp?PubID=2183 |access-date=27 September 2010 }}</ref> A subsequent international ban on hunting, [[sea otter conservation]] efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species 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]],  in [[California]], and in [[Russia]] have recently declined or have plateaued at depressed levels. The population in [[Japan]] likewise remains small and precarious. For these reasons, the sea otter remains classified as an [[endangered species]].

== Evolution ==
The sea otter is the heaviest (the [[giant otter]] is longer, but significantly slimmer) member of the family [[Mustelidae]],<ref name=adw>{{cite web |url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Enhydra_lutris.html|title=''Enhydra lutris''|access-date=24 November 2007 |work= Animal Diversity Web|publisher=University of Michigan Museum of Zoology}}</ref> a diverse group that includes the 13 [[otter]] species and terrestrial animals such as [[weasel]]s, [[badger]]s, and [[mink]]s. It is unique among the mustelids in not making [[:Category:Shelters built or used by animals|dens]] or [[burrow]]s, in having no functional [[anal scent glands]],<ref>[[#Kenyon|Kenyon]], p. 4</ref> and in being able to live its entire life without leaving the water.<ref name = vanblaricom11/> The only living 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 |date=December 1998 |title=Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome b sequences |journal=Journal of Zoology |volume= 246|issue=4 |pages=401–416 |doi= 10.1111/j.1469-7998.1998.tb00172.x|last1=Koepfli |first1=K.-P. |last2=Wayne |first2=R. K. }}</ref> [[Molecular phylogeny|Genetic]] analysis indicates the sea otter and its closest [[Extant taxon|extant]] relatives, which include the African [[speckle-throated otter]], [[Eurasian otter]], [[African clawless otter]] and [[Asian small-clawed otter]], shared an ancestor approximately 5&nbsp;million years ago.<ref name=koepfli2008>{{cite journal |author=Koepfli KP |title=Multigene phylogeny of the Mustelidae: resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation |journal=BMC Biology |volume=6 |page=10 |year=2008 |pmid=18275614 |pmc=2276185 |doi=10.1186/1741-7007-6-10 |author2=Deere KA |author3=Slater GJ |display-authors=3 |last4=Begg |first4=Colleen |last5=Begg |first5=Keith |last6=Grassman |first6=Lon |last7=Lucherini |first7=Mauro |last8=Veron |first8=Geraldine |last9=Wayne |first9=Robert K |doi-access=free }}</ref>

[[Fossil]] evidence indicates the ''Enhydra'' lineage became isolated in the North Pacific approximately 2&nbsp;million years ago, giving rise to the now-extinct ''[[Enhydra macrodonta]]'' and the modern sea otter, ''Enhydra lutris''.<ref name=love9>[[#Love|Love]], p. 9</ref> One related species has been described, ''[[Enhydra reevei]]'', from the [[Pleistocene]] of [[East Anglia]].<ref name=Willemsen1992>{{cite journal|author=Willemsen GF|year=1992 |title=A revision of the Pliocene and Quaternary Lutrinae from Europe|journal=Scripta Geologica |volume=101 |pages=1–115|citeseerx=10.1.1.738.4492 }}</ref><!-- If an article is created Enhydra reevei, this information would be relevant there: The [[holotype]], a lower carnassial, was in the [[Norwich Castle Museum]] but seems to be lost. Only one more specimen, an extremely worn lower carnassial, is known.--> The modern sea otter evolved initially in northern [[Hokkaidō]] and Russia, and then spread east to the [[Aleutian Islands]], mainland [[Alaska]], and down the North American coast.<ref>[[#Love|Love]], pp. 15–16</ref> In comparison to [[cetacea]]ns, [[sirenian]]s, and [[pinniped]]s, which entered the water approximately 50, 40, and 20&nbsp;million years ago, respectively, the sea otter is a relative newcomer to a marine existence.<ref>[[#Love|Love]], pp. 4–6</ref> In some respects, though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth.<ref>[[#Love|Love]], p. 6</ref> The full genome of the northern sea otter (''Enhydra lutris kenyoni'') was [[DNA sequencing|sequenced]] in 2017 and may allow for examination of the sea otter's [[Speciation|evolutionary divergence]] from terrestrial mustelids.<ref name="Jones2017">{{Cite journal |last1=Jones |first1=Samantha J |last2=Haulena |first2=Martin |last3=Taylor |first3=Gregory A |last4=Chan |first4=Simon |last5=Bilobram |first5=Steven |last6=Warren |first6=René L |last7=Hammond |first7=Austin |last8=Mungall |first8=Karen L |last9=Choo |first9=Caleb |display-authors=9 |last10=Kirk |first10=Heather |last11=Pawan |first11=Pandoh |last12=Ally |first12=Adrian |last13=Dhalla |first13=Noreen |last14=Tam |first14=Angela KY |last15=Troussard |first15=Armelle |last16=Paulino |first16=Daniel |date=11 December 2017 |title=The Genome of the Northern Sea Otter (''Enhydra lutris kenyoni'') |journal=Genes |volume=8 |issue=12 |page=379 |doi=10.3390/genes8120379|pmid=29232880 |pmc=5748697 |doi-access=free }}</ref>
Following their divergence from their most common ancestor five million years ago, sea otters have developed traits dependent on polygenic selection, or the evolution of numerous traits to create hallmark features like thick and oily [[fur]] and large bones, compared to their freshwater sister species.<ref name="Beichman-2019">{{Cite journal |last1=Beichman |first1=Annabel C |last2=Koepfli |first2=Klaus-Peter |last3=Li |first3=Gang |last4=Murphy |first4=William |last5=Dobrynin |first5=Pasha |last6=Kliver |first6=Sergei |last7=Tinker |first7=Martin T |last8=Murray |first8=Michael J |last9=Johnson |first9=Jeremy |last10=Lindblad-Toh |first10=Kerstin |last11=Karlsson |first11=Elinor K |last12=Lohmueller |first12=Kirk E |last13=Wayne |first13=Robert K |date=December 2019 |title=Aquatic Adaptation and Depleted Diversity: A Deep Dive into the Genomes of the Sea Otter and Giant Otter |journal=Molecular Biology and Evolution |volume=36 |issue=12 |pages=2631–2655 |doi=10.1093/molbev/msz101 |issn=0737-4038 |pmc=7967881 |pmid=31212313}}</ref> Sea otters require these traits to survive the cold waters of the northern [[Pacific Ocean]], in which they spend their entire lives despite occasionally coming out of the water as pups. Sea otters have the thickest fur of any animal (~1,000,000 hairs per square inch), as they do not have a [[blubber]] layer, while their [[Sebaceous gland|oil glands]] help matt down their fur and keep it from holding air.<ref name="Larson-2012">{{Cite journal |last1=Larson |first1=Shawn |last2=Jameson |first2=Ron |last3=Etnier |first3=Michael |last4=Jones |first4=Terry |last5=Hall |first5=Roberta |date=2012-03-05 |title=Genetic Diversity and Population Parameters of Sea Otters, Enhydra lutris, before Fur Trade Extirpation from 1741–1911 |journal=PLOS ONE |volume=7 |issue=3 |pages=e32205 |doi=10.1371/journal.pone.0032205 |doi-access=free |issn=1932-6203 |pmc=3293891 |pmid=22403635|bibcode=2012PLoSO...732205L }}</ref> Thick [[Bone|bones]] also prove crucial in increasing buoyancy, as sea otters spend long hours floating atop the ocean. In a study, southern and northern Sea Otter populations were compared against the [[African clawless otter]], and it was determined that aquatic traits like loss of smell and hair thickness independently evolved, evidencing a complex genome of [[Quantitative trait locus|polygenic traits]] resulting in complex systems.<ref name="Beichman-2019" /> This study was only able to take place after sequencing of Sea Otter nuclear genomes and through phylogeny to find a close ancestor with which to compare genomes. 

Previously, it was suspected that sea otters came from the same evolutionary branch as [[Earless seal|earless seals]], such as [[Harbor seal|harbor]] and [[Monk seal|monk seals]]. Sea Otters have experienced numerous population bottlenecks throughout their history, with significant numbers being wiped out 9,000-10,000 generations ago and 300–700 generations ago, long before the fur trade.<ref name="Beichman-2019" /> These previous genetic bottlenecks are responsible for already low genetic diversity amongst species members, making the secondary bottleneck caused by the fur trade more significant. These primary bottlenecks were most likely caused by disease, a common cause for genetic bottlenecks. Estimates place these bottlenecks at leaving around ten to forty animals for about eight to forty-four years.<ref name="Beichman-2019" /> This led to [[genetic drift]], as the populations of northern and southern sea otters were cut off from one another by thousands of miles, leading to significant [[Genomics|genomic]] differences. However, the modern population bottleneck caused by the fur trade of the eighteenth and early twentieth centuries presents the most significant concern to scientists and conservationists attempting to recover population numbers and genetic diversity. Each bottleneck has lowered genomic diversity and thus increased the chance of deleterious [[genetic drift]].

=== Taxonomy ===

{{cladogram
|caption=[[Cladogram]] showing relationships between sea otters and other otters<ref name=Koepfli2008>{{Cite journal |vauthors=Koepfli KP, Deere KA, Slater GJ, etal |title=Multigene phylogeny of the Mustelidae: Resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation |journal=BMC Biol. |volume=6 |pages=4–5 |year=2008 |pmid=18275614 |doi=10.1186/1741-7007-6-10 |pmc=2276185 |doi-access=free }}</ref><ref>{{Cite journal|vauthors=Bininda-Emonds OR, Gittleman JL, Purvis A |title=Building large trees by combining phylogenetic information: a complete phylogeny of the extant Carnivora (Mammalia) |journal=Biol Rev Camb Philos Soc |volume=74 |issue=2 |pages=143–75 |year=1999 |pmid=10396181 |doi=10.1111/j.1469-185X.1999.tb00184.x |url=http://www.molekularesystematik.uni-oldenburg.de/download/Publications/CarnivoreST.pdf |citeseerx=10.1.1.328.7194 }}</ref>
|clades={{clade |style=font-size:93%;line-height:110%
    |label1=[[Lutrinae]]
    |1={{clade
        |1=''[[Pteronura]]'' <small>(giant otter)</small>
        |2={{clade
            |1={{clade
                |1=''[[Lontra]]'' <small>(4 species)</small>
            }}
        |2={{clade
            |1='''''Enhydra''''' <small>(sea otter)</small>
            |2=''[[Hydrictis]]''<br /><small>(spotted-necked otter)</small>
            |3={{clade
                |1={{clade
                    |1=''[[Lutra]]'' <small>(2 species)</small>
                }}
                |2={{clade
                    |1={{clade
                        |1=[[African clawless otter|''Aonyx'']]<br /><small>(African clawless)</small>
                    }}
                    |2={{clade
                        |1=''[[Amblonyx]]''<br /><small>(Asian small-clawed)</small>
                        |2=[[Smooth-coated otter|''Lutrogale'']]<br /><small>(smooth-coated)</small>
                    }}
                }}
            }}
        }}
    }}
}} }}
}}

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]] in his landmark 1758 [[10th edition of Systema Naturae|10th edition of ''Systema Naturae'']].<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 | publisher = [[Oxford University Press]] | location = United Kingdom | isbn = 978-0-19-910207-5 | oclc = 17396377| title-link = A Greek-English Lexicon | edition = Abridged}}</ref> meaning "in the water", and the [[Latin]] word ''lutris'', meaning "otter".<ref>[[#Nickerson|Nickerson]], p. 19</ref> It was formerly sometimes referred to as the "sea [[beaver]]".<ref name = silverstein34/>

=== Subspecies ===
Three subspecies of the sea otter are recognized with distinct geographical distributions. ''Enhydra lutris lutris'' ([[Nominate subspecies|nominate]]), the '''Asian sea otter''', ranges across Russia's [[Kuril Islands]] northeast of Japan, and the [[Commander Islands]] in the northwestern Pacific Ocean. In the eastern Pacific Ocean, ''E. l. kenyoni'', the '''northern sea otter''', is found from Alaska's [[Aleutian Islands]] to Oregon and ''E. l. nereis'', the '''southern sea otter''', is native to central and southern California.<ref>{{Cite journal |last1=Campbell |first1=Kristin M. |last2=Santana |first2=Sharlene E. |s2cid=91055290 |date=3 October 2017 |title=Do differences in skull morphology and bite performance explain dietary specialization in sea otters? |url=http://faculty.washington.edu/ssantana/wordpress/wp-content/uploads/2013/02/Campbell-Santana_2017_Sea-otters_Small-file.pdf |journal=Journal of Mammalogy |volume=98 |page=1408 |doi=10.1093/jmammal/gyx091 |via=Oxford University Press|doi-access=free }}</ref> The Asian sea otter is the largest subspecies and has a slightly wider skull and shorter nasal bones than both other subspecies. Northern sea otters possess longer [[Jaw#Mammals|mandibles]] (lower jaws) while southern sea otters have longer [[Rostrum (anatomy)|rostrums]] and smaller teeth.<ref name="Wilson">{{Cite journal |last1=Wilson |first1=Don E. |last2=Bogan |first2=Michael A. |last3=Brownell |first3=Robert L. |last4=Burdin |first4=A. M. |last5=Maminov |first5=M. K. |date=13 February 1991 |title=Geographic Variation in Sea Otters, ''Enhydra lutris'' |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?&article=1090&context=usdeptcommercepub |journal=Journal of Mammalogy |volume=72 |issue=1 |pages=22–36 |doi=10.2307/1381977 |jstor=1381977 |via=University of Nebraska – Lincoln|url-access=subscription }}</ref><ref>{{Cite journal |last1=Timm-Davis |first1=Lori L. |last2=DeWitt |first2=Thomas J. |last3=Marshall |first3=Christopher D. |date=9 December 2015 |title=Divergent Skull Morphology Supports Two Trophic Specializations in Otters (Lutrinae) |journal=PLOS ONE|volume=10 |issue=12 |page=7 |doi=10.1371/journal.pone.0143236 |pmid=26649575 |pmc=4674116 |bibcode=2015PLoSO..1043236T |doi-access=free }}</ref>

== Description ==

[[File:Seaotterrocks.jpg|thumb|right|A sea otter's thick fur makes its body appear plumper on land than in the water.]]
[[File:Enhydra lutris skull - MUSE.JPG|thumb|Skull of a sea otter]]

The sea otter is one of the smallest [[marine mammal]] species, but it is the heaviest mustelid.<ref name=vanblaricom11>[[#VanBlaricom|VanBlaricom]], p. 11</ref> Male sea otters usually weigh {{convert|22|to|45|kg|abbr=on}} and are {{convert|1.2|to|1.5|m|abbr=on}} in length, though specimens up to {{convert|54|kg|abbr=on}} have been recorded.<ref>''The Wildlife Year''. The Reader's Digest Association, Inc. (1991). {{ISBN|0-276-42012-8}}</ref> Females are smaller, weighing {{convert|14|to|33|kg|abbr=on}} and measuring {{convert|1.0|to|1.4|m|abbr=on}} in length.<ref name=marinebio/> The average weight for adult sea otters that are in more densely populated areas, at {{convert|28.3|kg|lb|abbr=on}} in males and {{convert|21.1|kg|lb|abbr=on}} in females, was considerably lighter than the average weight of otters in more sparse populations, at {{convert|39.3|kg|lb|abbr=on}} in males and {{convert|25.2|kg|lb|abbr=on}} in females<ref name= Riedman/> Presumably less populous otters are more able to monopolize food sources,<ref name= Riedman/> For its size, the male otter's [[baculum]] is very large, massive and bent upwards, measuring {{convert|150|mm|abbr=on|frac=16}} in length and {{convert|15|mm|abbr=on|frac=16}} at the base.<ref name="h1342"/>

Unlike most other marine mammals, the sea otter has no [[blubber]] and relies on its exceptionally thick [[fur]] to keep warm.<ref name = nickerson21/> With up to {{convert|150000|/cm2||adj=pre| strands of hair}}, its fur is the densest of any animal.<ref>[[#Silverstein|Silverstein]], p. 14</ref> The fur consists of long, waterproof [[guard hairs]] and short underfur; the guard hairs keep the dense underfur layer dry.<ref name="marinebio" /> There is an air compartment between the thick fur and the skin where air is trapped and heated by the body.<ref name="Yeates-2007">{{Cite journal|last=Yeates|first=Laura|date=2007|title=Diving and foraging energetics of the smallest marine mammal, the sea otter (''Enhydra lutris'')|url=https://journals.biologists.com/jeb/article/210/11/1960/16829/Diving-and-foraging-energetics-of-the-smallest|journal=Journal of Experimental Biology|volume=210|issue=Pt 11|pages=1960–1970|doi=10.1242/jeb.02767|pmid=17515421|bibcode=2007JExpB.210.1960Y |s2cid=21944946|url-access=subscription}}</ref> Cold water is kept completely away from the skin and heat loss is limited.<ref name=marinebio>{{cite web |url=https://marinebio.org/species/sea-otters/enhydra-lutris/ |title= Sea Otters, ''Enhydra lutris''|website=MarineBio.org|date= 18 May 2017|access-date=30 August 2020 }}</ref> However, a potential disadvantage of this form of insulation is compression of the air layer as the otter dives, thereby reducing the insulating quality of fur at depth when the animal forages.<ref name="Yeates-2007" /> The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct [[molt]]ing season.<ref>[[#Kenyon|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|Love]], p. 21 and 28</ref> The coloration of the [[pelage]] is usually deep brown with silver-gray speckles, but it can range from yellowish or grayish brown to almost black.<ref name = love27>[[#Love|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|Silverstein]], p. 13</ref> The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully [[webbed foot|webbed]].<ref name = love21/> The fifth digit on each hind foot is longest, facilitating swimming while on its back, but making walking difficult.<ref name = "Kenyon_p70">[[#Kenyon|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|Silverstein]], p. 11</ref> The bones show [[osteosclerosis]], increasing their density to reduce buoyancy.<ref>{{cite journal|pmc=3615000|year=2013|last1=Hayashi|first1=S.|last2=Houssaye|first2=A.|last3=Nakajima|first3=Y.|last4=Chiba|first4=K.|last5=Ando|first5=T.|last6=Sawamura|first6=H.|last7=Inuzuka|first7=N.|last8=Kaneko|first8=N.|last9=Osaki|first9=T.|title=Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)|journal=PLOS ONE|volume=8|issue=4|pages=e59146|doi=10.1371/journal.pone.0059146|pmid=23565143|bibcode=2013PLoSO...859146H|doi-access=free}}</ref>

The sea otter presents an insight into the evolutionary process of the mammalian invasion of the [[Aquatic ecosystem|aquatic environment]], which has occurred numerous times over the course of mammalian evolution.<ref>{{Cite journal |last1=Yuan |first1=Yuan |last2=Zhang |first2=Yaolei |last3=Zhang |first3=Peijun |last4=Liu |first4=Chang |last5=Wang |first5=Jiahao |last6=Gao |first6=Haiyu |last7=Hoelzel |first7=A. Rus |last8=Seim |first8=Inge |last9=Lv |first9=Meiqi |last10=Lin |first10=Mingli |last11=Dong |first11=Lijun |last12=Gao |first12=Haoyang |last13=Yang |first13=Zixin |last14=Caruso |first14=Francesco |last15=Lin |first15=Wenzhi |date=2021-09-14 |title=Comparative genomics provides insights into the aquatic adaptations of mammals |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=37 |pages=e2106080118 |doi=10.1073/pnas.2106080118 |issn=0027-8424 |pmc=8449357 |pmid=34503999|bibcode=2021PNAS..11806080Y |doi-access=free }}</ref> Having only returned to the sea about 3 million years ago,<ref>{{Cite journal |last=Liwanag |first=Heather |date=December 2012 |title=Morphological and thermal properties of mammalian insulation: the evolutionary transition to blubber in pinnipeds |journal=Biological Journal of the Linnean Society |volume=107 |issue=4 |pages=774–787|doi=10.1111/j.1095-8312.2012.01992.x |doi-access=free }}</ref> sea otters represent a snapshot at the earliest point of the transition from fur to blubber. In sea otters, fur is still advantageous, given their small nature and division of lifetime between the aquatic and terrestrial environments.<ref name="Mostman Liwanag-2008">{{Cite thesis |last=Mostman Liwanag |first=Heather Elizabeth |date=2008 |title=Fur versus Blubber: A comparative look at marine mammal insulation and its metabolic and behavioral consequences |type=PhD dissertation |publisher=University of California, Santa Cruz |url=https://www.researchgate.net/publication/234015183 |isbn=978-0-549-93125-6 |id={{ProQuest|304663143}} }}</ref> However, as sea otters evolve and adapt to spending more and more of their lifetimes in the sea, the [[convergent evolution]] of blubber suggests that the reliance on fur for insulation would be replaced by a dependency on blubber. This is particularly true due to the diving nature of the sea otter; as dives become lengthier and deeper, the air layer's ability to retain heat or [[buoyancy]] decreases,<ref name="Yeates-2007" /> while blubber remains efficient at both of those functions.<ref name="Mostman Liwanag-2008" /> Blubber can also additionally serve as an energy source for deep dives,<ref>{{Cite journal |last=Koopman |first=Heather N. |date=2018-03-07 |title=Function and evolution of specialized endogenous lipids in toothed whales |journal=The Journal of Experimental Biology |volume=221 |issue=Pt Suppl 1 |pages=jeb161471 |doi=10.1242/jeb.161471 |issn=1477-9145 |pmid=29514890|s2cid=3789040 |doi-access=free |bibcode=2018JExpB.221B1471K }}</ref> which would most likely prove advantageous over fur in the evolutionary future of sea otters.  

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|Love]], p. 21</ref> and is capable of speeds of up to {{convert|9|km/h}}.<ref name=adw/> When underwater, its body is long and streamlined, with the short forelimbs pressed closely against the chest.<ref>[[#Kenyon|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|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|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 similar-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'')|access-date=23 February 2008|archive-url=https://web.archive.org/web/20081208185746/http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=A0A7|archive-date=8 December 2008}}</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=vanblaricom1121>[[#VanBlaricom|VanBlaricom]], p. 11 and 21</ref> Researchers have noted when they approach in plain view, sea otters react more rapidly when the wind is blowing towards the animals, indicating the sense of [[Olfaction|smell]] is more important than [[Visual perception|sight]] as a warning sense.<ref>[[#Kenyon|Kenyon]], p. 55</ref> Other observations indicate the sea otter's sense of sight is useful above and below the water, although not as good as that of seals.<ref>[[#Love|Love]], p. 23</ref> Its [[hearing (sense)|hearing]] is neither particularly acute nor poor.<ref>[[#Kenyon|Kenyon]], p. 56</ref>

An adult's 32 [[teeth]], particularly the [[Molar (tooth)|molars]], are flattened and rounded for crushing rather than cutting food.<ref>[[#Kenyon|Kenyon]], p. 43</ref> [[Pinniped|Seals]] and sea otters are the only [[carnivore]]s with two pairs of lower [[incisor]] teeth rather than three;<ref>[[#Love|Love]], p. 74</ref> the adult [[dentition|dental formula]] is {{DentalFormula|upper=3.1.3.1|lower=2.1.3.2}}.<ref>[[#Kenyon|Kenyon]], p. 47</ref> The teeth and bones are sometimes stained purple as a result of ingesting sea urchins.<ref>{{Cite journal|last1=Winer|first1=J.N.|last2=Liong|first2=S.M.|last3=Verstraete|first3=F.J.M.|date=2013|title=The Dental Pathology of Southern Sea Otters (''Enhydra lutris nereis'')|journal=Journal of Comparative Pathology|language=en|volume=149|issue=2–3|pages=346–355|doi=10.1016/j.jcpa.2012.11.243|pmid=23348015}}</ref>
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 to burn the calories necessary to counteract the loss of heat due to the cold water environment.<ref>[[#VanBlaricom|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|access-date=13 December 2007|archive-url = https://web.archive.org/web/20080216083821/http://wlapwww.gov.bc.ca/wld/documents/otter.pdf |archive-date = 16 February 2008}}</ref> Its digestive efficiency is estimated at 80 to 85%,<ref>[[#Love|Love]], p.24</ref> and food is digested and passed in as little as three hours.<ref name = nickerson21/> Most of its need for water is met through food, although, in contrast to most other marine mammals, it also drinks seawater. Its relatively [[Reniculate kidney|large kidneys]] enable it to derive fresh water from sea water and excrete concentrated urine.<ref>{{cite journal |author=Ortiz RM |title=Osmoregulation in marine mammals |journal=The Journal of Experimental Biology |volume=204 |issue=11 |pages=1831–44 |date=June 2001 |doi=10.1242/jeb.204.11.1831 |pmid=11441026 |url=http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=11441026|doi-access=free |bibcode=2001JExpB.204.1831O }}</ref>

== Behavior ==
[[File:sea otter with sea urchin.jpg|thumb|right|Sensitive [[vibrissa]]e and forepaws enable sea otters to find prey (like this [[Strongylocentrotus purpuratus|purple sea urchin]]) 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|Love]], pp. 69–70</ref> Foraging resumes for a few hours in the afternoon and subsides before sunset, and a third foraging period may occur 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|Love]], pp. 70–71</ref>

Sea otters spend much of their 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 casual observers, it appears as if the animals are scratching, but they are not known to have [[lice]] or other parasites in the fur.<ref>[[#Kenyon|Kenyon]], p. 76</ref> When eating, sea otters roll in the water frequently, apparently to wash food scraps from their fur.<ref name=wp/>
[[File:Sea otter cleaning.jpg|left|thumb|A sea otter grooming itself by rubbing its dense coat.]]

=== Foraging ===
{{see also|Physiology of underwater diving}}
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"/> its dives typically last about one minute and not more than four minutes.<ref name=marinebio/> It is the only marine animal capable of lifting and turning over rocks, which it often does with its front paws when searching for prey.<ref name=wp>{{cite video |people=Reitherman, Bruce |date= 1993 |title=Waddlers and Paddlers: A Sea Otter Story–Warm Hearts & Cold Water |medium= Documentary |publisher= [[Public Broadcasting Service|PBS]]|location= U.S.A.}}</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|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, and sometimes a rock that is used to break open shellfish and clams.<ref name=haley>{{cite book|title=Marine Mammals of Eastern North Pacific and Arctic Waters|edition=2nd|chapter=Sea Otter|year=1986|location=Seattle, Washington|publisher=Pacific Search Press|isbn=978-0-931397-14-1|editor=Haley, D.|oclc=13760343}}</ref> At the surface, 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/> 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|access-date=31 December 2007}}</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|VanBlaricom]], p. 22</ref>

The sea otter's [[Tool use by sea otters|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/>

=== Social structure ===
[[File:Sea otters holding hands, cropped.jpg|thumb|left|Sleeping sea otters holding paws are kept afloat by their naturally high buoyancy.]]

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|Love]], p. 49</ref> The largest raft ever seen contained over 2000 sea otters. To keep themselves from drifting out to sea when resting and eating, sea otters may wrap themselves in [[kelp]].<ref>[[#VanBlaricom|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|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 that 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|Love]], p. 50</ref>

The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a [[gull]].<ref name = kenyon77/> Females coo when they are apparently content; males may grunt instead.<ref>[[#Kenyon|Kenyon]], pp. 78–79</ref> Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream.<ref name=kenyon77>[[#Kenyon|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|Silverstein]], p. 61</ref> They spend much time alone, and each adult can meet its own hunting, grooming, and defense needs.<ref name=Silverstein61/>

=== Reproduction and life cycle ===
[[File:Sea otter with injured nose.JPG|thumb|right|While mating the male bites the nose of the female, often bloodying and scarring it.]]

Sea otters are [[Polygyny in animals|polygynous]]: males have multiple female partners, typically those that inhabit their territory. If no territory is established, they seek out females in estrus. When a male sea otter finds a receptive female, the two engage in playful and sometimes aggressive behavior. They bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior.<ref name=adw/><ref>At least one female is known to have died from an infected nose. ([[#Love|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/> [[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|Love]], p. 54</ref> In California, sea otters usually breed every year, about twice as often as those in Alaska.<ref>[[#Silverstein|Silverstein]], p. 30</ref>

Birth usually takes place in the water and typically produces a single pup weighing {{convert|1.4 to 2.3|kg|lboz}}.<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|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, the pup floats like a cork and cannot dive.<ref>[[#Love|Love]], pp. 56–61</ref> The fluffy baby fur is replaced by adult fur after about 13 weeks.<ref name=wdfw/>
[[File:Sea otter nursing02.jpg|thumb|left|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/>]]
[[Lactation|Nursing]] lasts six to eight months in Californian populations and four to twelve months in Alaska, with the mother beginning to offer bits of prey at one to two months.<ref>[[#Silverstein|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|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, but a mother may be forced to abandon a pup if she cannot find enough food for it;<ref name=love63>[[#Love|Love]], p. 63</ref> at the other extreme, a pup may be nursed until it is almost adult size.<ref name=Nowak/> Pup mortality is high, particularly during an individual's first winter&nbsp;– by one estimate, only 25% of pups survive their first year.<ref name="love63" /> Pups born to experienced mothers have the highest survival rates.<ref>[[#Love|Love]], p. 62</ref>

Females perform all tasks of feeding and raising offspring, and have occasionally been observed caring for orphaned pups.<ref>[[#Love|Love]], p. 59</ref> Much has been written about the level of devotion of sea otter mothers for their pups&nbsp;– 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|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|Silverstein]], p. 31</ref> if the pup is not sleeping, it cries loudly until she returns.<ref>[[#Silverstein|Silverstein]], p. 28</ref> Mothers have been known to carry their pups for days after the pups' deaths.<ref name=love58>[[#Love|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|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 Johns Hopkins University Press|location=Baltimore and London|year=1991|isbn=978-0-8018-3970-2|pages=[https://archive.org/details/walkersmammalsof01nowa/page/1141 1141–1143]|url=https://archive.org/details/walkersmammalsof01nowa/page/1141}}</ref> In the wild, sea otters live to a maximum age of 23 years,<ref name=marinebio/> with lifespans ranging from 10 to 15 years for males and 15–20 years for females.<ref>[[#VanBlaricom|VanBlaricom]], p. 71</ref> Several captive individuals have lived past 20 years. The [[Seattle Aquarium]] was home to both the oldest recorded female, Etika, who lived to the age of 28, and the oldest recorded male, [[Adaa (sea otter)|Adaa]], who lived to be 22 years 8 months.<ref>[[#VanBlaricom|VanBlaricom]], pp. 40–41</ref> Sea otters in the wild often develop worn [[teeth]], which may account for their apparently shorter lifespans.<ref>[[#VanBlaricom|VanBlaricom]], p. 41</ref>

== Population and distribution ==

Sea otters live in coastal waters {{convert|15 to 23|m|0}} deep,<ref name=silverstein17>[[#Silverstein|Silverstein]], p. 17</ref> and usually stay within a kilometre ({{frac|2|3}}&nbsp;mi) of the shore.<ref>[[#Nickerson|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|Silverstein]], p. 19</ref> Although they are most strongly associated with rocky [[substrate (marine biology)|substrates]], sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt.<ref>[[#VanBlaricom|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|Kenyon]], p. 133</ref> Individuals generally occupy a home range a few kilometres long, and remain there year-round.<ref name=love6769>[[#Love|Love]], pp. 67–69</ref>

The sea otter population is thought to have once been 150,000 to 300,000,<ref name = silverstein34/> stretching in an arc across the North Pacific from northern Japan to the central [[Baja California 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 13 colonies. Hunting records researched by historian Adele Ogden place the westernmost limit of the hunting grounds off the northern Japanese island of [[Hokkaido]] and the easternmost limit off [[Punta Morro Hermosa]] about {{convert|21+1/2|mi|km}} south of [[Punta Eugenia]], [[Baja California Sur|Baja California's]] westernmost headland in [[Mexico]].<ref name=Ogden/>

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, with reports of recolonizations in Mexico and Japan.<ref>[[#VanBlaricom|VanBlaricom]], p. 54</ref> Population estimates made between 2004 and 2007 give a worldwide total of approximately 107,000 sea otters.<ref name=wdfw/><ref name=Kornev/><ref name=alaskafws/><ref name=bc/><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 |agency=Associated Press |access-date=25 December 2007 |archive-url=https://web.archive.org/web/20110108012300/http://www.mailtribune.com/apps/pbcs.dll/article?AID=%2F20070615%2FLIFE%2F706150317 |archive-date=8 January 2011 }}</ref> However, much more recent counts of the sea otter population in areas such as the [[Aleutian Islands]] in Alaska and the [[Sea of Okhotsk]] along the coast of Russia have shown steep declines in recent years, casting doubt on those estimates.<ref name="Popov">{{cite journal |last1=Popov |first1=Igor |last2=Iurmanov |first2=Anton |title=Recent surveys of the sea otter (Enhydra lutris) population on Kuril Islands |journal=Pacific Conservation Biology |date=October 2024 |volume=30 |issue=6 |page=24026 |doi=10.1071/PC24026 |bibcode=2024PacSB..3024026P |url=https://www.researchgate.net/publication/385182819}}</ref><ref name="Ryazanov">{{cite journal |last1=Ryazanov |first1=Sergey D. |last2=Fomin |first2=Sergey V. |title=Mercury content in the fur of sea otters (Enhydra lutris) from the Commander Islands |journal=Marine Pollution Bulletin |date=March 2023 |volume=188 |doi=10.1016/j.marpolbul.2023.114638 |pmid=36706549 |bibcode=2023MarPB.18814638R |url=https://www.sciencedirect.com/science/article/abs/pii/S0025326X23000693}}</ref> 

=== Japan ===
Adele Ogden wrote in ''The California Sea Otter Trade'' that western sea otter were hunted "from Yezo northeastward past the [[Kuril Islands|Kuril Group]] and [[Kamchatka Peninsula|Kamchatka]] to the [[Aleutian Islands|Aleutian Chain]]".<ref name=Ogden/> "Yezo" refers to the island province of [[Hokkaido]], in northern Japan, where the country's only confirmed population of western sea otter resides.<ref name="iucn status 11 November 2021">{{cite iucn |author=Doroff, A. |author2=Burdin, A. |date=2015 |title=''Enhydra lutris'' |volume=2015 |page=e.T7750A21939518 |doi=10.2305/IUCN.UK.2015-2.RLTS.T7750A21939518.en |access-date=11 November 2021}}</ref> Sightings have been documented in the waters of [[Cape Nosappu]], [[Erimo, Hokkaido|Erimo]], [[Hamanaka, Hokkaido|Hamanaka]] and [[Nemuro, Hokkaido|Nemuro]], among other locations in the region.<ref>{{cite web|url= https://www.inaturalist.org/observations?place_id=6737&subview=map&taxon_id=41860|title=Observations, iNaturalist|accessdate=14 November 2023|website=[[iNaturalist]]}}</ref> 

The last count estimated around 50 sea otters living off the coast of eastern Hokkaido. The Etopirika Foundation (エトピリカ基金), a small non-profit organization run by Yoshihiro Kataoka, monitors the local sea otter population and researches ways to protect them.<ref>{{cite news |last1=Yamamoto |first1=Tomoyuki |title=Sea otters are bouncing back in wild, but tourism posing a threat |url=https://www.asahi.com/ajw/articles/15327446 |publisher=Asahi Shimbun |date=27 July 2024}}</ref> In April 2025, Kataoka documented the first lethal case of [[avian influenza]] among sea otters.<ref>{{cite news |last1=竹中 |first1=達哉 |title=ラッコが鳥インフル感染 浜中で国内初 |url=https://www.hokkaido-np.co.jp/article/1154540/ |access-date=28 May 2025 |publisher=Hokkaido Shimbun |date=30 April 2025}}</ref>

=== Russia ===
Most of the western sea otter's population is found along the [[Russian Far East]] coastline, in the northwestern Pacific waters off of the country (namely [[Kamchatka]] and [[Sakhalin Island]]), occasionally being seen in and around the [[Sea of Okhotsk]].<ref name=vb62/> Before the 19th century, around 20,000 to 25,000 sea otters lived near the [[Kuril Islands]], with more near 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/> Circa 2004, sea otters had repopulated all of their former habitat in these areas, with an estimated total population at the time of about 27,000; of these, about 19,000 were at the Kurils, 2,000 to 3,500 were at Kamchatka and another 5,000 to 5,500 were at the Commander Islands.<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''. pp. 273–278.{{dead link|date=May 2025}}</ref> 

However, much more recent surveys from the years 2019-2024 showed steep declines in all of these populations. The latest numbers put the number of sea otters around the Kuril Islands at a mere 3,000, and at 1,673 and 1,565 sea otters around the Commander Islands and Kamchatka peninsula, respectively.<ref name="Popov" /><ref name="Ryazanov" /> Continued illegal poaching in Russia is believed to contribute to these declines.<ref name="Popov" /><ref>{{cite journal |last1=Popov |first1=Igor |last2=Scopin |first2=Alexey |title=The historical and contemporary status of the sea otter Enhydra lutris population on Urup Island, southern Kuril Islands |journal=Oryx |date=July 2021 |volume=55 |issue=4 |pages=529–534 |doi=10.1017/S0030605320000812 |url=https://www.cambridge.org/core/journals/oryx/article/historical-and-contemporary-status-of-the-sea-otter-enhydra-lutris-population-on-urup-island-southern-kuril-islands/BA07C0C0EA0D63ABF859B04DA2184040}}</ref> Russian NGOs such as the Nature and People Foundation have increased their efforts to bring attention to the plight of Russia's sea otter population.<ref>{{cite web |title=Сохраняем удивительных каланов |url=https://naturepeople.ru/projects/kalan |website=Природа и люди}}</ref> 

=== British Columbia ===
Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with the last sea otter taken near [[Kyuquot, British Columbia|Kyuquot]] in 1929. From 1969 to 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island. This population increased to over 5,600 in 2013 with an estimated annual growth rate of 7.2%, and their range on the island's west coast extended north to [[Cape Scott Provincial Park|Cape Scott]] and across the Queen Charlotte Strait to the [[Broughton Archipelago]] and south to [[Clayoquot Sound]] and [[Tofino]].<ref name="2013 Survey">{{cite web |title=Trends in the Abundance and Distribution of Sea Otters (''Enhydra lutris'') in British Columbia Updated with 2013 Survey Results|publisher=Department of Fisheries and Oceans, Canada |url=https://waves-vagues.dfo-mpo.gc.ca/Library/365073.pdf |date=July 2015|access-date=10 July 2018}}</ref><ref>{{cite web |title=Sea Otter Recovery on Vancouver Island's West Coast |publisher=Bamfield Marine Sciences Centre Public Education Programme |url=http://www.oceanlink.info/seaotterstewardship/history1.html |access-date=22 August 2011 }}</ref> In 1989, a separate colony was discovered in the central British Columbia coast. It is not known if this colony, which numbered about 300 animals in 2004, was founded by transplanted otters or was a remnant population that had gone undetected.<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 |access-date=11 December 2007 |archive-url=https://web.archive.org/web/20060917054125/http://www.vanaqua.org/aquanew/fullnews.php?id=1692 |archive-date=17 September 2006 }}</ref> By 2013, this population exceeded 1,100 individuals, was increasing at an estimated 12.6% annual rate, and its range included [[Aristazabal Island]], and [[Milbanke Sound]] south to [[Calvert Island (British Columbia)|Calvert Island]].<ref name="2013 Survey"/> In 2008, Canada determined the status of sea otters to be "special concern".<ref>[http://www.sararegistry.gc.ca/species/speciesDetails_e.cfm?sid=149 Sea Otter], Species at Risk Public Registry</ref><ref>[http://www.dfo-mpo.gc.ca/science/publications/article/2010/11-25-10-eng.html Sea Otters], Fisheries and Oceans Canada</ref>

===United States===

==== Alaska ====
[[Alaska]] is the central area of the sea otter's range. In 1973, the population in Alaska was estimated at between 100,000 and 125,000 animals.<ref>[[#Nickerson|Nickerson]], p. 46</ref> By 2006, though, 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&nbsp;– Southwest Alaska Sea Otter Recovery Team (SWAKSORT)|publisher=U.S. Fish and Wildlife Service&nbsp;– Alaska|access-date=15 January 2008|archive-url=https://web.archive.org/web/20080206201842/http://alaska.fws.gov/fisheries/mmm/seaotters/recovery.htm|archive-date=6 February 2008}}</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 as one factor.<ref name=Schrope/> The population in [[Prince William Sound]] was also severely affected by the [[Exxon Valdez oil spill|''Exxon Valdez'' oil spill]], which killed thousands of sea otters in 1989.<ref name=wp/>

==== Washington ====
In 1969 and 1970, 59 sea otters were translocated from [[Amchitka Island]] to [[Washington (state)|Washington]], and released near [[La Push]] and [[Point Grenville]]. The translocated population is estimated to have declined to between 10 and 43 individuals before increasing, reaching 208 individuals in 1989. As of 2017, the population was estimated at over 2,000 individuals, and their range extends from Point Grenville in the south to [[Cape Flattery]] in the north and east to Pillar Point along the [[Strait of Juan de Fuca]].<ref name=wdfw>{{cite web |id= (link: [http://wdfw.wa.gov/wlm/diversty/soc/recovery/seaotter/index.htm WDFW seaotter]) |title= Washington State Periodic Status Review for the Sea Otter |publisher= Washington Department of Fish and Wildlife |url= https://wdfw.wa.gov/publications/01965/wdfw01965.pdf |access-date= 10 July 2018 |archive-url= https://web.archive.org/web/20180710185113/https://wdfw.wa.gov/publications/01965/wdfw01965.pdf |archive-date = 10 July 2018}}</ref>

In Washington, sea otters are found almost exclusively on the outer coasts. They can swim as close as six feet off shore along the Olympic coast. Reported sightings of sea otters in the [[San Juan Islands]] and [[Puget Sound]] almost always turn out to be [[North American 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/>

==== Oregon ====
The last native sea otter in Oregon was probably shot and killed in 1906. In 1970 and 1971, a total of 95 sea otters were transplanted from [[Amchitka Island]], Alaska to the Southern Oregon coast. However, this translocation effort failed and otters soon again disappeared from the state.<ref name=Jameson>{{Cite thesis |last=Jameson |first=Ronald James |year=1975 |title=An Evaluation of Attempts to Reestablish the Sea Otter in Oregon |type=MSc |publisher=Oregon State University |url=http://ir.library.oregonstate.edu/jspui/bitstream/1957/6719/1/Jameson_Ronald_J_ocr.pdf |archive-url=https://wayback.archive-it.org/all/20170525111401/http://ir.library.oregonstate.edu/jspui/bitstream/1957/6719/1/Jameson_Ronald_J_ocr.pdf |archive-date=25 May 2017 |access-date=30 December 2009 |hdl=1957/6719 |oclc=9653603 }}</ref> In 2004, a male sea otter took up residence at Simpson Reef off of Cape Arago for six months. This male is thought to have originated from a colony in Washington, but disappeared after a coastal storm.<ref>{{cite news |title=Sea otter's stay raises scientists' hopes |url=http://www.ecotrust.org/nativeprograms/Seaottersstay.04.quinn.pdf |date=17 October 2004 |access-date=30 December 2009 |work=The Oregonian |first=Beth |last=Quinn |archive-url=https://web.archive.org/web/20101230175203/http://www.ecotrust.org/nativeprograms/Seaottersstay.04.quinn.pdf |archive-date=30 December 2010 }}</ref> On 18 February 2009, a male sea otter was spotted in [[Depoe Bay]] off the [[Oregon Coast]]. It could have traveled to the state from either California or Washington.<ref name=oregonian>{{cite news|title=Rare sea otter confirmed at Depoe Bay|url=http://blog.oregonlive.com/terryrichard/2009/02/rare_sea_otter_confirmed_at_de.html#more|date=20 February 2009|access-date=27 February 2009|work=The Oregonian}}</ref>

==== California ====
[[File:CalifCentralCoast.jpg|thumb|California's remote areas of coastline sheltered small colonies of sea otters through the fur trade. The 50 that survived in California, which were rediscovered in 1938, have since reproduced to almost 3,000.]]

The historic population of California sea otters was estimated at 16,000 before the fur trade decimated the population, leading to their assumed extinction. Today's population of California sea otters are the descendants of a single colony of about 50 sea otters located near [[Bixby Creek Bridge]] in March 1938.<ref>[[#Silverstein|Silverstein]], p. 41</ref> Their principal range has gradually expanded and extends from [[Pigeon Point Lighthouse|Pigeon Point]] in [[San Mateo County]] to [[Santa Barbara County]].<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|access-date=23 February 2008|archive-date=29 June 2010|archive-url=https://web.archive.org/web/20100629125359/http://www.werc.usgs.gov/otters/ca-surveyspr2007.htm|url-status=dead}}</ref>

Sea otters were once numerous in [[San Francisco Bay]].<ref>{{Cite web|last=Rogers|first=Paul|date=2020-12-11|title=Are sea otters taking a bite out of California's Dungeness crab season?|url=https://www.mercurynews.com/2020/12/11/are-sea-otters-taking-a-bite-out-of-californias-dungeness-crab-season |access-date=2020-12-12|website=The Mercury News|language=en-US}}</ref><ref>[http://www.nrdc.org/greengate/wildlife/otterf.asp Southern Sea Otters] {{Webarchive|url=https://web.archive.org/web/20111130140619/http://www.nrdc.org/greengate/wildlife/otterf.asp |date=30 November 2011 }}. nrdc.org</ref> Historical records revealed the [[Russian-American Company]] snuck [[Aleut people|Aleuts]] into San Francisco Bay multiple times, despite the Spanish capturing or shooting them while hunting sea otters in the estuaries of [[San Jose, California|San Jose]], [[San Mateo, California|San Mateo]], [[San Bruno, California|San Bruno]] and around [[Angel Island (California)|Angel Island]].<ref name=Ogden>{{cite book |title=The California sea otter trade, 1784–1848 |author=Ogden, Adele |year=1975 |page=54 |publisher=University of California Press |location=Berkeley, California |isbn=978-0-520-02806-7 |url=https://books.google.com/books?id=mlU37uRbvmcC&pg=PA196}}</ref> The founder of [[Fort Ross]], [[Ivan Kuskov]], finding otters scarce on his second voyage to Bodega Bay in 1812, sent a party of Aleuts to San Francisco Bay, where they met another Russian party and an American party, and caught 1,160 sea otters in three months.<ref>{{cite book |title=History of Alaska: 1730–1885 |author1=Bancroft, Hubert Howe |author2=Bates, Alfred |author3=Petroff, Ivan |author4=Nemos, William |url=https://archive.org/details/bub_gb_HQQTAAAAYAAJ|page=[https://archive.org/details/bub_gb_HQQTAAAAYAAJ/page/n521 482] |year=1887 |publisher=A. L. Bancroft & Company |location=San Francisco, California |access-date=26 September 2010 }}</ref> By 1817, sea otters in the area were practically eliminated and the Russians sought permission from the Spanish and the Mexican governments to hunt further and further south of San Francisco.<ref>{{cite report |title=Archeological Research Issues for the Point Reyes National Seashore – Golden Gate National Recreation Area |author1=Stewart, Suzanne |author2=Praetzellis, Adrian |page=335 |url=http://www.sonoma.edu/asc/projects/pointreyes/overview4.pdf |date=November 2003 |publisher=Anthropological Studies Center, Sonoma State University |access-date=26 September 2010 }}</ref> In 1833, fur trappers [[George Nidever]] and [[George Calvert Yount|George Yount]] canoed "along the Petaluma side of [the] Bay, and then proceeded to the [[San Joaquin River]]", returning with sea otter, beaver, and river otter pelts.<ref>{{cite journal |title=The Chronicles of George C. Yount: California Pioneer of 1826 |author=Charles L. Camp |author2=George C. Yount |date=April 1, 1923 |journal=California Historical Society Quarterly |volume=2 |issue=1 |pages=3–66 |doi=10.2307/25177691 |jstor=25177691 |url=https://www.jstor.org/stable/pdf/25177691.pdf |access-date=June 28, 2023}}</ref>  Remnant sea otter populations may have survived in the bay until 1840, when the [[Rancho Punta de Quentin]] was granted to Captain [[John B. R. Cooper]], a sea captain from Boston, by Mexican Governor [[Juan Bautista Alvarado]] along with a license to hunt sea otters, reportedly then prevalent at the mouth of [[Corte Madera Creek (Marin County, California)|Corte Madera Creek]].<ref name=RossHistory>{{cite book |title=Ross, California – The people, the places, the history |publisher=Ross Historical Society |date=May 2008 |url=https://www.amazon.com/Ross-California-People-Places-History/dp/B006CARGSQ|access-date=3 November 2010 |last1=Battersby |first1=Bob |last2=Maginis |first2=Preston |last3=Nielsen |first3=Susan |last4=Scales |first4=Gary |last5=Torney |first5=Richard |last6=Wynne |first6=Ed }}</ref>

In the late 1980s, the USFWS relocated about 140 southern 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 majority of the San Nicolas sea otters swam back to the mainland.<ref name=santacruz/> Another group of twenty swam {{convert|74|mi|km}} north to [[San Miguel Island]], where they were captured and removed.<ref>[[#mcLeish|mcLeish]], p. 32</ref> By 2005, only 30 sea otters remained at San Nicolas,<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|access-date=10 April 2008}}</ref> although they were slowly increasing as they thrived on the abundant prey around the island.<ref name=santacruz/> The plan that authorized the translocation program had predicted the carrying capacity would be reached within five to 10 years.<ref>{{cite news |title=Service Proposes to End Southern Sea Otter Translocation Program |publisher=USFWS Pacific Southwest Region |date=17 August 2011 |url=http://www.fws.gov/cno/press/release.cfm?rid=253 |access-date=21 December 2012 }}</ref> The spring 2016 count at San Nicolas Island was 104 sea otters, continuing a 5-year positive trend of over 12% per year.<ref name="Hatfield-2016"/> Sea otters were observed twice in Southern California in 2011, once near Laguna Beach and once at Zuniga Point Jetty, near San Diego. These are the first documented sightings of otters this far south in 30 years.<ref>{{cite news |title=Rare sighting of sea otter off Laguna Beach |publisher=KABC-TV/DT |date=7 December 2011 |url=https://abc7.com/archive/8458657/ |access-date=8 December 2011 |url-status=live |archive-url=https://web.archive.org/web/20131021013356/http://abclocal.go.com/kabc/story?section=news%2Fbizarre&id=8458657 |archive-date=21 October 2013 }}</ref>

When the USFWS implemented the translocation program, it also attempted, in 1986, to implement "zonal management" of the Californian 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 many translocated otters died and also as it proved impractical to capture the hundreds of otters which ignored regulations and swam into the zone.<ref>{{cite news|title=Balance sought in sea otter conflict|url=http://www.cnn.com/NATURE/9903/24/otters.enn/|date=24 March 1999|access-date=25 January 2008|publisher=CNN}}</ref> However, after engaging in a period of public commentary in 2005, the Fish and Wildlife Service failed to release a formal decision on the issue.<ref name=fws/> Then, in response to lawsuits filed by the Santa Barbara-based Environmental Defense Center and the Otter Project, on 19 December 2012 the USFWS declared that the "no otter zone" experiment was a failure, and will protect the otters re-colonizing the coast south of Point Conception as threatened species.<ref>{{cite news |title=U.S. will let otters roam along Southern California coastline |author=Weiss, Kenneth R. |newspaper=Los Angeles Times |date=20 December 2012 |url=http://www.latimes.com/news/local/la-me-otters-20121220,0,6969607.story |access-date=21 December 2012 }}</ref> Although abalone fisherman blamed the incursions of sea otters for the decline of abalone, commercial abalone fishing in southern California came to an end from overfishing in 1997, years before significant otter moved south of Point Conception. In addition, [[white abalone]] (''Haliotis sorenseni''), a species never overlapping with sea otter, had declined in numbers 99% by 1996, and became the first marine invertebrate to be federally listed as endangered.<ref>[[#mcLeish|mcLeish]], p. 264</ref>

Although the southern sea otter's range has continuously expanded from the remnant population of about 50 individuals in [[Big Sur]] since protection in 1911, from 2007 to 2010, the otter population and its range contracted and since 2010 has made little progress.<ref name=USGS /><ref>{{cite web |title=California Sea Otter Numbers Drop Again |author=Young Landis, Ben |author2=Tinker, Tim |author3=Hatfield, Brian |publisher=U. S. Geological Survey |date=3 August 2010 |url=https://archive.usgs.gov/archive/sites/soundwaves.usgs.gov/2010/12/index.html |access-date=23 January 2011 |archive-date=25 June 2020 |archive-url=https://web.archive.org/web/20200625020926/https://archive.usgs.gov/archive/sites/soundwaves.usgs.gov/2010/12/index.html  }}</ref> As of spring 2010, the northern boundary had moved from about [[Tunitas Creek]] to a point {{convert|2|km}} southeast of [[Pigeon Point Lighthouse|Pigeon Point]], and the southern boundary has moved along the [[Gaviota Coast]] from approximately [[Coal Oil Point]] to [[Gaviota State Park]].<ref>{{cite web |title=Spring 2010 Mainland California Sea Otter Survey Results |publisher=USGS Western Ecological Research Center |url=http://www.werc.usgs.gov/ProjectSubWebPage.aspx?SubWebPageID=16&ProjectID=91&List=SubWebPages&Web=Project_91&Title=Sea%20Otter%20Studies%20at%20WERC |archive-url=https://web.archive.org/web/20110612020558/http://www.werc.usgs.gov/ProjectSubWebPage.aspx?SubWebPageID=16&ProjectID=91&List=SubWebPages&Web=Project_91&Title=Sea%20Otter%20Studies%20at%20WERC |url-status=dead |archive-date=12 June 2011 |access-date=26 September 2010 }}</ref> A toxin called [[microcystin]], produced by a type of [[cyanobacteria]] (''[[Microcystis]]''), seems to be concentrated in the shellfish the otters eat, poisoning them. Cyanobacteria are found in stagnant water enriched with nitrogen and phosphorus from septic tank and agricultural fertilizer runoff, and may be flushed into the ocean when streamflows are high in the rainy season.<ref>{{cite news |title=Another deadly challenge for the sea otter |author=Weiss, Kenneth R. |newspaper=Los Angeles Times |date=23 September 2010 |url=http://www.latimes.com/news/local/la-me-sea-otters-20100923,0,3239917.story |access-date=10 November 2010 }}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0012576 |title=Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters  |journal=PLOS ONE|volume=5 |issue=9 |pages=e12576 |date=2010 |pmid=20844747 |pmc=2936937 |author=Miller MA |author2=Kudela RM |author3=Mekebri A |author4=Crane D |author5=Oates SC |display-authors=5 |editor1-last=Thompson |editor1-first=Ross |last6=Tinker |first6=M. Timothy |last7=Staedler |first7=Michelle |last8=Miller |first8=Woutrina A. |last9=Toy-Choutka |first9=Sharon |bibcode=2010PLoSO...512576M |doi-access=free }}</ref> A record number of sea otter carcasses were found on California's coastline in 2010, with increased shark attacks an increasing component of the mortality.<ref>{{cite news |title=Sea otter deaths jump in 2010 |author=Colliver, Victoria |work=San Francisco Chronicle |date=23 January 2011 |url=http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/01/22/BA4K1HCS7T.DTL |access-date=23 January 2011 }}</ref> [[Great white shark]]s do not consume relatively fat-poor sea otters but shark-bitten carcasses have increased from 8% in the 1980s to 15% in the 1990s and to 30% in 2010 and 2011.<ref>{{cite journal |title=Number of dead California sea otters a record high in 2011 |author=USGS |journal=Marine Pollution Bulletin |date=April 2012 |doi=10.1016/j.marpolbul.2012.03.002|volume=64|issue=4 |pages=671–674 }}</ref>
[[File:Sea otter kelp forest Chumash Heritage National Marine Sanctuary.PNG|thumb|300px|A sea otter in a [[kelp forest]] off the [[Central Coast (California)|Central Coast]] of [[California]] in the waters of the [[Chumash Heritage National Marine Sanctuary]].]]
For southern sea otters to be considered for removal from threatened species listing, the [[U.S. Fish and Wildlife Service]] (USFWS) determined that the population should exceed 3,090 for three consecutive years.<ref name=USGS>{{cite web |title=California's Sea Otter Numbers Continue Slow Climb |publisher=[[USGS]] |date=12 September 2013 |url=http://www.usgs.gov/newsroom/article.asp?ID=3687 |access-date=20 October 2013 }}</ref> In response to recovery efforts, the population climbed steadily from the mid-20th century through the early 2000s, then remained relatively flat from 2005 to 2014 at just under 3,000. There was some contraction from the northern (now [[Pigeon Point Lighthouse|Pigeon Point]]) and southern limits of the sea otter's range during the end of this period, circumstantially related to an increase in lethal shark bites, raising concerns that the population had reached a plateau.<ref name=WERC>{{cite report |title=Spring 2014 California Sea Otter Census Results |last1=Hatfield |first1=Brian |last2=Tinker |first2=Tim |date=22 September 2014 |url=http://www.werc.usgs.gov/ProjectSubWebPage.aspx?SubWebPageID=24&ProjectID=91 |access-date=6 December 2015 }}</ref> However, the population increased markedly from 2015 to 2016, with the [[United States Geological Survey]] (USGS) California sea otter survey 3-year average reaching 3,272 in 2016, the first time it exceeded the threshold for delisting from the [[Endangered Species Act]] (ESA).<ref name="Hatfield-2016">{{cite report |title=Annual California Sea Otter Census – 2016 Spring Census Summary |last1=Hatfield |first1=B.B. |last2=Tinker |first2=M.T. |website=USGS Western Ecological Research Center |date=19 September 2016 |doi=10.5066/F7FJ2DWJ |doi-access=free}}</ref> If populations continued to grow and ESA delisting occurred, southern sea otters would still be fully protected by state regulations and the [[Marine Mammal Protection Act]], which set higher thresholds for protection, at approximately 8,400 individuals.<ref>{{cite news |title=Southern Sea Otter |publisher=USFWS, Ventura Fish and Wildlife Office |url=https://www.fws.gov/ventura/endangered/species/info/sso.html |access-date=28 December 2016 |archive-date=29 December 2016 |archive-url=https://web.archive.org/web/20161229014906/https://www.fws.gov/ventura/endangered/species/info/sso.html  }}</ref> However, ESA delisting seems unlikely due to a precipitous population decline recorded in the spring 2017 USGS sea otter survey count, from the 2016 high of 3,615 individuals to 2,688, a loss of 25% of the California sea otter population.<ref>{{cite report |title=California sea otter (''Enhydra lutris nereis'') census results, spring 2017 |last1=Tinker |first1=M. T. |last2=Hatfield |first2=B. B. |chapter=California sea otter (Enhydra lutris nereis) census results, Spring 2017 |series=Data Series |publisher=U.S. Geological Survey Data Series 1067 |date=29 September 2017 |page=9 |doi=10.3133/ds1067|doi-access=free }}</ref>

=== Mexico ===
Historian Adele Ogden described sea otters as being particularly abundant in "Lower California", now the [[Baja California Peninsula]], where "seven bays...were main centers". The southernmost limit was Punta Morro Hermoso about {{convert|21+1/2|mi|km}} south of [[Punta Eugenia]], in turn a headland at the southwestern end of [[Sebastián Vizcaíno Bay]], on the west coast of the Baja Peninsula. Otter were also taken from [[San Benito Island]], [[Cedros Island]], and [[Isla Natividad]] in the Bay.<ref name=Ogden/> By the early 1900s, Baja's sea otters were extirpated by hunting. In a 1997 survey, small numbers of sea otters, including pups, were reported by local fishermen, but scientists could not confirm these accounts.<ref>{{cite journal |title=Status of Sea Otters (''Enhydra Lutris'') in Mexico |vauthors= Gallo-Reynoso JP, Rateibun GB |journal=Marine Mammal Science |volume=13 |issue=2 |pages=332–340 |year=1997 |doi=10.1111/j.1748-7692.1997.tb00639.x|bibcode= 1997MMamS..13..332G }}</ref> However, male and female otters have been confirmed by scientists off shores of the Baja Peninsula in a 2014 study, who hypothesize that otter dispersed there beginning in 2005. These sea otters may have dispersed from [[San Nicolas Island]], which is {{convert|300|km|mi}} away, as individuals have been recorded traversing distances of over {{convert|800|km|mi}}. Genetic analysis of most of these animals were consistent with California, i.e. United States, otter origins, however one otter had a haplotype not previously reported, and could represent a remnant of the original native Mexican otter population.<ref>{{cite journal |title=New evidence for the existence of southern sea otters (''Enhydra lutris nereis'') in Baja California, Mexico |vauthors=Schramm Y, Heckel G, Sáenz-Arroyo A, López-Reyes E, Baez-Flores A, Gómez-Hernández G, Lazode-la-Vega-Trinker A, Lubinsky-Jinich D, de los Angeles Milanés-Salinas M |year=2014 |journal=Marine Mammal Science |volume=30 |issue=3 |pages=1264–1271 |doi=10.1111/mms.12104|bibcode=2014MMamS..30.1264S }}</ref>

== Ecology ==

=== Diet ===
[[File:Otter with mussels & barnacles.jpg|thumb|This female otter has gathered mussels and gooseneck barnacles from a wharf piling and is in the process of eating them.]]High energetic requirements of sea otter [[metabolism]] require them to consume at least 20% of their body weight a day.<ref name="Yeates-2007" /> Surface swimming and [[foraging]] are major factors in their high energy expenditure due to drag on the surface of the water when swimming and the thermal heat loss from the body during deep dives when foraging.<ref>{{Cite journal|last=Williams|first=Terrie|date=1989|title=Swimming by sea otters: adaptations for low energetic cost locomotion|url=https://www.researchgate.net/publication/225208596|journal=Journal of Comparative Physiology A|volume=164|issue=6|pages=815–824|doi=10.1007/BF00616753|pmid=2724187|s2cid=1926452}}</ref><ref name="Yeates-2007" /> Sea otter muscles are specially adapted to generate heat without physical activity.<ref>{{cite news |last1=Wright |first1=Traver |last2=Sheffield-Moore |first2=Melinda |last3=Davis |first3=Randall |title=Sea otters demonstrate that there is more to muscle than just movement – it can also bring the heat |url=https://theconversation.com/sea-otters-demonstrate-that-there-is-more-to-muscle-than-just-movement-it-can-also-bring-the-heat-165804 |access-date=8 December 2021 |work=[[The Conversation (website)|The Conversation]] |date=2 December 2021}}</ref>

Sea otters are [[apex predators]] that consume over 100 prey species.<ref name="v1829" /><ref>{{cite journal |last1= Williams|first1= Perry J.|last2= Hooten|first2= Mevin B.|last3= Esslinger|first3= George G.|last4= Womble|first4= Jamie N.|last5= Bodkin|first5= James L.|last6= Bower|first6= Michael R.|display-authors=3|date= 2018-11-29|title= The rise of an apex predator following deglaciation|journal= Biodiversity Research|volume= 25|issue= 6|pages= 895–908|doi= 10.1111/ddi.12908|doi-access= free}}</ref> In most of its range, the sea otter's diet consists almost exclusively of marine [[Benthos|benthic]] invertebrates, including [[sea urchin]]s (such as ''[[Strongylocentrotus franciscanus]]'' and ''[[Strongylocentrotus purpuratus|S. purpuratus]]''), [[sea star]]s (''[[Pisaster ochraceus]]''), [[sea cucumber]]s, [[Urechis caupo|fat innkeeper worms]], [[crustacean]]s, a variety of [[mollusk]]s such as [[chiton]]s (such as ''[[Katharina tunicata]]''),  [[snail]]s such as [[abalone]]s and [[limpet]]s (such as ''[[Diodora aspera]]''), and [[bivalve]]s such as [[clam]]s, [[mussel]]s (such as ''[[Mytilus edulis]]''), and scallops (such as ''[[Crassadoma gigantea]]'').<ref name="v1829" /><ref>{{Cite web |date=2011-02-02 |title=Elkhorn Slough Mammals: Sea Otter |url=http://elkhornslough.org/sloughlife/mammals/sea_otter.htm |access-date=2023-04-08 |archive-date=2 February 2011 |archive-url=https://web.archive.org/web/20110202105224/http://elkhornslough.org/sloughlife/mammals/sea_otter.htm  }}</ref><ref>{{Cite web |last=Gunderson |first=Joe Allegra; Rhiannon Rath; Aren |title=Enhydra lutris (sea otter) |url=https://animaldiversity.org/accounts/Enhydra_lutris/ |access-date=2023-04-08 |website=Animal Diversity Web |language=en}}</ref><ref>{{cite journal | pmc=10154889 | date=2023 | last1=Laroche | first1=N. L. | last2=King | first2=S. L. | last3=Fergusson | first3=E. A. | last4=Eckert | first4=G. L. | last5=Pearson | first5=H. C. | title=Macronutrient composition of sea otter diet with respect to recolonization, life history, and season in southern Southeast Alaska | journal=Ecology and Evolution | volume=13 | issue=5 | pages=e10042 | doi=10.1002/ece3.10042 | pmid=37153015 | bibcode=2023EcoEv..1310042L }}</ref> Its prey ranges in size from tiny [[limpet]]s and [[crab]]s to [[giant octopus]]es.<ref name="v1829">[[#VanBlaricom|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, they have been noted to ignore [[Pismo clam]]s smaller than {{convert|3|in}} across.<ref>[[#Love|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|Kenyon]], p. 121</ref> The fish species were usually bottom-dwelling and sedentary or sluggish forms, such as ''[[Hemilepidotus hemilepidotus]]'' and family [[Tetraodontidae]].<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 name=wdfw/><ref>[[#Love|Love]], p. 76</ref> 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|Kenyon]], p. 119</ref> Sea otters will also occasionally prey on seabirds. In California, the most commonly eaten species were [[western grebe]]s, although [[cormorant]]s, [[gull]]s, [[common loon]]s, and [[surf scoter]]s were also consumed.<ref>{{cite journal |last1=Estes |first1=James A. |last2=Riedman |first2=Marianne L. |title=Predation on seabirds by sea otters |journal=Canadian Journal of Zoology |date=1988 |volume=66 |issue=6 |pages=1396–1402|doi=10.1139/z88-205 }}</ref>

The individuals within a particular area often differ in their foraging methods and prey types, and tend to follow the same patterns as their mothers.<ref>[[#VanBlaricom|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|VanBlaricom]], p. 30</ref> however, they never completely wipe out a prey species from an area.<ref>[[#Nickerson|Nickerson]], p. 57</ref> A 2007 Californian study demonstrated, in areas where food was relatively scarce, a wider variety of prey was consumed. Surprisingly, though, the diets of individuals were more specialized in these areas than in areas where food was plentiful.<ref name=santacruz>{{cite web|url=https://www.sciencedaily.com/releases/2008/01/080114173901.htm|title=Sea Otter Show Striking Variability in Diets And Feeding Strategies|author=University of California&nbsp;– Santa Cruz|publisher=ScienceDaily|date=18 January 2008|access-date=20 January 2008}}</ref>

=== As a keystone species ===
[[File:Kelp-forest-Monterey.jpg|thumb|upright|Sea otters control herbivore populations, ensuring sufficient coverage of kelp in [[kelp forest]]s]]

Sea otters are a classic example of a [[keystone species]]; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain [[benthic]] (sea floor) herbivores, particularly [[sea urchin]]s, in check.<ref name="Womble-2016" /> Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die.<ref>{{Cite news |last=Chrobak|first=Ula|date=2021-09-15|title=How sea otters can fight climate change|url=https://www.bbc.com/future/article/20210914-how-sea-otters-help-fight-climate-change |access-date=2021-12-11|publisher=BBC|language=en}}</ref> 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/> Kelp forests are extremely productive ecosystems. Kelp forests sequester (absorb and capture) CO<sub>2</sub> from the atmosphere through photosynthesis. Sea otters may help mitigate effects of climate change by their cascading trophic influence.<ref>{{cite web|last=Sezen |first=Uzay|title=Otters vs. Climate Change – KQED/QUEST (2014)|date=29 May 2017 |website=Nature Documentaries |url=http://naturedocumentaries.org/7010/otters-vs-climate-change-kqedquest-2014/|access-date=6 June 2017}}</ref>

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&nbsp;– Species Profile&nbsp;– Sea Otter|website=[[Fisheries and Oceans Canada]]|access-date=29 November 2007|archive-url = https://web.archive.org/web/20071123064622/http://www.dfo-mpo.gc.ca/species-especes/species/species_seaOtter_e.asp |archive-date = 23 November 2007}}</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/> 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/> 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|VanBlaricom]], p. 33</ref>

Sea otters affect rocky ecosystems that are dominated by [[mussel]] beds by removing mussels from rocks. This allows space for competing species and increases species diversity.<ref name="vanblaricom33"/>

=== Predators ===
The leading mammalian predators of this species is the [[orca]]. [[California sea lion|Sea lion]]s and [[bald eagle]]s may prey on pups.<ref name=vanaqua/> On land, young sea otters may face attack from bears and [[coyote]]s. In California, great white sharks are their primary predator,<ref name = Nickerson65>{{cite web|author=Nickerson, P.|url=http://www.defenders.org/programs_and_policy/wildlife_conservation/imperiled_species/sea_otter/publications_and_facts/faqs.php|title=Sea Otter Frequently Asked Questions|publisher=Defenders of Wildlife|page=65|access-date=31 August 2011|archive-url=https://web.archive.org/web/20110709102511/http://www.defenders.org/programs_and_policy/wildlife_conservation/imperiled_species/sea_otter/publications_and_facts/faqs.php <!--Added by H3llBot-->|archive-date=9 July 2011}}</ref> though this is the result of mistaking otters for seals and they do not consume otters after biting them.<ref>{{Cite book |last=McLeish |first=Todd |title=Return of the sea otter: the story of the animal that evaded extinction on the Pacific Coast |date=2018 |publisher=Sasquatch Books |isbn=978-1-63217-137-5 |location=Seattle}}</ref> In [[Katmai National Park]], [[wolf|grey wolves]] have been recorded to hunt and kill sea otters.<ref>{{cite web |last1=Kobilinsky |first1=Dana |title=Wolves prey on sea otters, seals in Katmai |url=https://wildlife.org/wolves-prey-on-sea-otters-seals-in-katmai/ |website=The Wildlife Society |access-date=4 December 2023 |date=1 December 2023}}</ref>

[[Urban runoff]] transporting cat feces into the ocean brings ''[[Toxoplasma gondii]]'', an [[obligate parasite]] of felids, which has killed sea otters.<ref>{{cite web|url=https://caseagrant.ucsd.edu/sites/default/files/Conrad_CZ169.pdf|title=Parasite Shed in Cat Feces Kills Sea Otters – California Sea Grant|website=www-csgc.ucsd.edu}}</ref> Parasitic infections of ''[[Sarcocystis neurona]]'' are also associated with human activity.<ref name="Jones2017" /> According to the U.S. Geological Survey and the CDC, northern sea otters off Washington have been infected with the [[H1N1 flu virus]] and "may be a newly identified animal host of influenza viruses".<ref>{{cite web | url=http://www.usgs.gov/newsroom/article.asp?ID=3864 | title=Sea Otters Can Get the Flu, Too | publisher=U.S. Department of the Interior, U.S. Geological Survey | date=8 April 2014 | access-date=11 April 2014 | author=Rogall, Gail Moede}}</ref>

== Relationship with humans ==

=== Fur trade ===
[[File:Sea otter hunters 1896.jpg|thumb|upright|[[Aleut people|Aleut]] men in [[Unalaska]] in 1896 used waterproof [[kayak]] gear and garments to hunt sea otters.]]

Sea otters have the thickest fur of any mammal, which makes them a common target for many hunters. Archaeological evidence indicates that for thousands of years, [[indigenous peoples]] have hunted sea otters for food and fur. Large-scale hunting, part of the [[Maritime Fur Trade]], which would eventually kill approximately one million sea otters, began in the 18th century 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/>

In the early 18th century, Russians began to hunt sea otters in the Kuril Islands<ref name=silverstein34>[[#Silverstein|Silverstein]], p. 34</ref> and sold them to the Chinese at [[Kyakhta]]. 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. In 1741, on his second North Pacific voyage, Bering was shipwrecked off [[Bering Island]] in the [[Commander Islands]], where he and many of his crew died. 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. They returned to Siberia, having killed nearly 1,000 sea otters, and were able to command high prices for the pelts.<ref name=silverstein35>[[#Silverstein|Silverstein]], p. 35</ref> Thus began what is sometimes called the "Great Hunt", which would continue for another hundred years. The Russians found the sea otter far more valuable than the [[sable]] skins that had driven and paid for most of their expansion across Siberia. If the sea otter pelts brought back by Bering's survivors had been sold at Kyakhta prices they would have paid for one tenth the cost of Bering's expedition.<ref>James R Gibson (1969) ''Feeding the Russian Fur Trade''. University of Wisconsin Press. p. 17. {{ISBN|0299052338}}</ref>

[[File:London Sea Otter pelt sales 1871-1910.svg|thumb|left|Pelt sales (in thousands) in the London fur market – the decline 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 people|Aleuts]] 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 the hunters had introduced.<ref name = silverstein37/>{{Disputed inline|date=March 2021}} The Aleut population was reduced, by the Russians' own estimate, from 20,000 to 2,000.<ref name="Gedney">{{Cite web |last=Gedney, Larry |date=6 May 1983 |title=The Aleut and the Otter |url=http://www.gi.alaska.edu/ScienceForum/ASF6/605.html |archive-url=https://web.archive.org/web/20070610101614/http://www.gi.alaska.edu/ScienceForum/ASF6/605.html |archive-date=2007-06-10 |access-date=23 February 2008}}</ref> By the 1760s, the Russians had reached [[Alaska]]. In 1799, [[Tsar Paul I]] consolidated the rival fur-hunting companies into the [[Russian-American Company]], granting it an imperial charter and protection, and a monopoly over trade rights and territorial acquisition.
Under [[Aleksander I]], the administration of the merchant-controlled company was transferred to the Imperial Navy, largely due to the alarming reports by naval officers of native abuse; in 1818, the indigenous peoples of Alaska were granted civil rights equivalent to a townsman status in the Russian Empire.<ref name=Middleton8>[[#Middleton|Middleton]], p. 8</ref>

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 [[Indigenous peoples of the Americas|Native Americans]] and sold them in Asia.<ref name=silverstein37>[[#Silverstein|Silverstein]], p. 37</ref> In 1778, British explorer [[Captain James Cook]] reached [[Vancouver Island]] and bought sea otter furs from the First Nations people. 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.<ref name=silverstein38>[[#Silverstein|Silverstein]], p. 38</ref>

Russian hunting expanded to the south, initiated by American ship captains, who subcontracted Russian supervisors and Aleut hunters<ref name=Farris21/> in what are now Washington, Oregon, and California. Between 1803 and 1846, 72 American ships were involved in the otter hunt in California, harvesting an estimated 40,000 skins and tails, compared to only 13 ships of the Russian-American Company, which reported 5,696 otter skins taken between 1806 and 1846.<ref name=Mathes326/> In 1812, the Russians founded an agricultural settlement at what is now [[Fort Ross, California|Fort Ross]] in northern California, as their southern headquarters.<ref name = silverstein38/>
Eventually, sea otter populations became so depleted, commercial hunting was no longer viable. It had stopped in the Aleutian Islands, by 1808, as a conservation measure imposed by the Russian-American Company. Further restrictions were ordered by the company in 1834.<ref name=Middleton4>[[#Middleton|Middleton]], p. 4</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 [[Local extinction|extirpated]] the sea otter again.<ref name=silverstein40>[[#Silverstein|Silverstein]], p. 40</ref> Prices rose as the species became rare. During the 1880s, a pelt brought $105 to $165 in the London market, but 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 [[North Pacific Fur Seal Convention of 1911|Treaty for the Preservation and Protection of Fur Seals]], imposing a moratorium on the harvesting of sea otters.<ref>[[#VanBlaricom|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}}
[[File:OilSheenFromValdezSpill.jpg|thumb|right|In the wake of the March 1989 [[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 considered one of the greatest successes in marine conservation.<ref>[[#VanBlaricom|VanBlaricom]], p. 53</ref> However, the [[IUCN]] still 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&nbsp;– sea otters can drown if entangled in fishing gear.<ref name="iucn status 11 November 2021" /> The hunting of sea otters is no longer legal except for limited harvests by [[indigenous peoples]] in the United States.<ref>[[#VanBlaricom|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|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]]|access-date=5 December 2007}}</ref> to which they are particularly vulnerable, since they rely on their fur to keep warm. When their fur is soaked with oil, it loses its ability to retain air, and the animals can quickly die 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|''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=https://www.usatoday.com/news/nation/2007-01-31-exxon-alaska_x.htm|title=Damage of Exxon Valdez endures|agency=Associated Press|date=31 January 2007|access-date=25 December 2001|work=USA Today|first1=Elizabeth|last1=Weise}}</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:

{{blockquote|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 a single major spill could be catastrophic for that state or province.<ref name=wdfw/><ref name=wlap/><ref name=wp/> Prevention of oil spills and preparation to rescue otters if one happens is a major focus for conservation efforts. Increasing the size and 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|Nickerson]], pp. 47–48</ref>
With a population size of fifty, the low genetic diversity amongst the population post-fur trade but pre-discovery produced an [[Population bottleneck|evolutionary bottleneck]]. The recent population constraints put on the sea otter have led to low genomic diversity among species members, with much evidence of inbreeding.<ref name="Larson-2012" /> This inbreeding has led to the mutation of deleterious [[Missense mutation|missense mutations]], which may make fast-paced population growth difficult for conservation reasons. While longer-term recovery goals bolstering genetic diversity by inbreeding are costly and challenging, they could significantly aid in avoiding the further evolution of deleterious variation, thus aiding sea otter population stabilization. This method has already been utilized in returning cheetah populations to higher numbers and higher genetic diversity, and captive breeding programs through organizations such as the [[Monterey Bay Aquarium]] and [[The Marine Mammal Center]] make the chances of getting sea otter populations back up to pre-fur trade numbers possible. The population of sea otters in California has risen to around 3,000 in the wild.<ref name="Conrad-2013">{{Cite web |last=Conrad |first=Kristin |title=In Search of the California Sea Otter |url=https://www.bbc.com/travel/article/20130329-in-search-of-the-california-sea-otter |website=BBC.com|date=9 April 2013 }}</ref> While this figure is far below pre-fur trade numbers, it represents a massive improvement in the conservation of the species and a massive increase in genetic diversity. On the other hand, northern sea otters have reached back up to pre-fur trade population numbers, with populations living all along the state's coast from [[Ketchikan, Alaska|Ketchikan]] in the south to [[Attu Island|Attu]] in the west. Historical populations, however, are estimated to have been between 150,000 and 300,000 individuals living along the northern Pacific rim from [[Baja California]] to [[Hokkaido|Hokkaido Island]] in Japan. Modern conservation techniques have included breeding northern and southern populations of sea otters to increase genetic diversity and prevent both inbreeding and genetic drift. Moreover, the introduction of the [[Marine Mammal Protection Act]] in the 1970s made their hunting highly illegal in the United States.

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 news|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|access-date=4 December 2007|publisher=CNN}}</ref> The most widely accepted, but still controversial, hypothesis is that killer whales have been eating the otters. The pattern of disappearances is consistent with a rise in predation, but there has been no direct evidence of orcas preying on sea otters to any significant extent.<ref name=Schrope>{{cite journal |author=Schrope M |s2cid=4421362 |title=Food chains: killer in the kelp |journal=Nature |volume=445 |issue=7129 |pages=703–5 |date=February 2007 |pmid=17301765 |doi=10.1038/445703a|bibcode=2007Natur.445..703S |doi-access=free }}</ref>
Another area of concern is California, where recovery began to fluctuate or decline in the late 1990s.<ref name = ASLC/> Unusually high mortality rates amongst adult and subadult otters, particularly females, have been reported.<ref name="Leff" /> In 2017 the US Geological Survey found a 3% drop in the sea otter population of the California coast. This number still keeps them on track for removal from the endangered species list, although just barely.<ref>{{cite news|title=Sea otter census finds 3% decline |author=Steve Rubenstein |page=C1 |work=San Francisco Chronicle |date=2 October 2017}}</ref> [[Necropsies]] of dead sea otters indicate diseases, particularly ''[[Toxoplasma gondii]]'' and [[acanthocephala]]n parasite infections, are major causes of sea otter mortality in California.<ref name=kreuder>{{cite journal |author=Kreuder C |title=Patterns of mortality in southern sea otters (''Enhydra lutris nereis'') from 1998–2001 |journal=Journal of Wildlife Diseases |volume=39 |issue=3 |pages=495–509 |date=July 2003 |pmid=14567210 |author2=Miller MA |author3=Jessup DA |display-authors=3 |last4=Lowenstine |first4=LJ |last5=Harris |first5=MD |last6=Ames |first6=JA |last7=Carpenter |first7=TE |last8=Conrad |first8=PA |last9=Mazet |first9=JA |s2cid=8595917 |doi=10.7589/0090-3558-39.3.495|doi-access=free }}</ref> The ''Toxoplasma gondii'' parasite, which is often fatal to sea otters, is carried by wild and domestic cats and may be transmitted by domestic cat droppings flushed into the ocean via sewage systems.<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|access-date=24 November 2007|archive-url=https://web.archive.org/web/20071225205629/http://www.magazine.noaa.gov/stories/mag72.htm|archive-date=25 December 2007}}</ref> Although disease has clearly 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/>

[[File:Sea otter pair2.jpg|thumb|Sea otters off the coast of [[Washington (state)|Washington]], within the [[Olympic Coast National Marine Sanctuary]]]]

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|access-date=19 March 2008}}</ref> An estimated 1,200 sea otters live within the [[Monterey Bay National Marine Sanctuary]], and more than 500 live within the [[Olympic Coast National Marine Sanctuary]].<ref>{{cite web |title=Sea otter |url=https://www.montereybayaquarium.org/animals/animals-a-to-z/sea-otter |access-date=2 October 2023 |website=Monterey Bay Aquarium |publisher=}}</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|access-date=19 March 2008|archive-date=20 August 2008|archive-url=https://web.archive.org/web/20080820101012/http://olympiccoast.noaa.gov/living/history_and_culture/history/welcome.html}}</ref>

=== Economic impact ===
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 because sea otters have sometimes been held responsible for declines of shellfish stocks that were more likely caused by [[overfishing]], disease, pollution, and [[seismic]] activity.<ref name=wp/><ref name=Love9398>[[#Love|Love]], pp. 93–98</ref> Shellfish declines have also occurred in many parts of the North American Pacific coast that do not have sea otters, and conservationists sometimes note the existence of large concentrations of shellfish on the coast is a recent development resulting from the fur trade's near-[[Local extinction|extirpation]] of the sea otter.<ref name=Love9398/> Although many factors affect shellfish stocks, sea otter predation can deplete a fishery to the point where it is no longer commercially viable.<ref name=vb34/> Scientists agree that sea otters and abalone fisheries cannot exist in the same area,<ref name=vb34>[[#VanBlaricom|VanBlaricom]], p. 34</ref> and the same is likely true for certain other types of shellfish, as well.<ref name=cnn/>

Many facets of the interaction between sea otters and the human economy 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|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|Nickerson]], p. 70</ref> ''E. lutris'' is a controlling predator of the [[red king crab]] (''Paralithodes camtschaticus'') in the Bering Sea, which would otherwise be out of control as it is in its [[invasive species|invasive range]], the [[Barents Sea]].<ref name="Petersen-et-al-2011">{{cite journal | last1=Falk-Petersen | first1=Jannike | last2=Renaud | first2=Paul | last3=Anisimova | first3=Natalia | title=Establishment and ecosystem effects of the alien invasive red king crab (''Paralithodes camtschaticus'') in the Barents Sea–a review | journal=[[ICES Journal of Marine Science]] | publisher=[[International Council for the Exploration of the Sea]] ([[Oxford University Press|OUP]]) | volume=68 | issue=3 | date=2011-01-12 | issn=1095-9289 | doi=10.1093/icesjms/fsq192 | pages=479–488}}</ref> (Berents otters, ''[[Lutra lutra]]'', occupy the same ecological niche and so are believed to help to control them in the Berents but this has not been studied.)<ref name="Petersen-et-al-2011" /> 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 popular [[tourist attraction]]s, bringing visitors to local hotels, restaurants, and sea otter-watching expeditions.<ref name=Silverstein49/>

=== Roles in human cultures ===

{|class="graytable" style="text-align:left"
| style="width:20%;"|[[File:AleutKalan1.jpg|center|60px]]
| style="width:80%;"|[[File:AleutKalan2.jpg|center|600px|Aleut carving of a sea otter hunt]]
<small> '''Left''': [[Aleut people|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 [[Peter the Great Museum of Anthropology and Ethnography]] in [[St. Petersburg]]. 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>{{qn|date=February 2024}} </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 people |Aleut]] in the Aleutian Islands, the [[Haida people |Haida]] of [[Haida Gwaii]]<ref name="uwo.academia">{{Cite journal |author1= Szpak, Paul |author2= Orchard, Trevor J. |author3= McKechnie, Iain |author4= Gröcke, Darren R. |year= 2012 |title= Historical Ecology of Late Holocene Sea Otters (''Enhydra lutris'') from Northern British Columbia: Isotopic and Zooarchaeological Perspectives | url=https://uwo.academia.edu/PaulSzpak/Papers/1216885/Historical_Ecology_of_Late_Holocene_Sea_Otters_Enhydra_lutris_from_Northern_British_Columbia_Isotopic_and_Zooarchaeological_Perspectives |journal=[[Journal of Archaeological Science]] |volume= 39 |issue= 5 |pages= 1553–1571 |doi= 10.1016/j.jas.2011.12.006 |bibcode= 2012JArSc..39.1553S }}</ref> 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. 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, regarded the sea otter as particularly kin to humans. The [[Nuu-chah-nulth people| Nuu-chah-nulth]], Haida, and other [[First Nations in Canada |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= https://thetyee.ca/News/2007/10/04/SeaOtter1/|title=Too Many Sea Otters?|author= Okerlund, Lana|date=4 October 2007|access-date=15 January 2007}}</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|Love]], pp 34–35</ref>

Some [[Ainu people|Ainu]] folk-tales portray the sea-otter as an occasional messenger between humans and the creator.<ref name=Basil>{{Cite book | author=Chamberlain, B. | title=Aino Folk Tales | publisher=The Folk-Lore society, private printing | place=London | year=1888 | url=https://en.wikisource.org/wiki/Aino_Folk-Tales }}</ref> The sea otter is a recurring figure in Ainu folklore. A major Ainu [[Yukar |epic]], the ''[[Kutune Shirka]]'', tells the tale of wars and struggles over a golden sea-otter. Versions of a widespread Aleut legend tell of lovers or despairing women who plunge into the sea and become otters.<ref>{{cite journal|author= Golder, F. A. |year= 1905|title= Aleutian Stories|journal= The Journal of American Folklore|volume= 18|issue= 70|pages= 215–222|doi= 10.2307/533140|jstor= 533140}}</ref> These stories 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">Barabash-Nikiforov, N. I. (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|access-date= 15 January 2007}}</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|Love]], p. 97</ref>

=== Aquariums and zoos ===
[[File:Otter playing - 2015 11 08.ogv|thumb|A sea otter in captivity in [[Japan]], 2015]]
Sea otters can do well in [[Captivity (animal)|captivity]], and are featured in over 40 [[public aquarium]]s and [[zoo]]s.<ref>[[#VanBlaricom|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=19 April 2000 |publisher=Business Wire |access-date=9 March 2007 |url=http://www.allbusiness.com/transportation/marine-transportation-marine-accidents/6425408-1.html |archive-url=https://web.archive.org/web/20090619040524/http://www.allbusiness.com/transportation/marine-transportation-marine-accidents/6425408-1.html |archive-date=19 June 2009 }}</ref> In 2007, a [[YouTube]] video of two sea otters holding paws drew 1.5&nbsp;million viewers in two weeks, and had over 22&nbsp;million views {{As of|2022|7|lc=y}}.<ref>{{cite web |title=Otters holding hands |url=https://www.youtube.com/watch?v=epUk3T2Kfno | archive-url=https://ghostarchive.org/varchive/youtube/20211114/epUk3T2Kfno| archive-date=2021-11-14 | url-status=live|author=cynthiaholmes |date=19 March 2007 |via=YouTube |access-date=24 March 2008}}{{cbignore}}</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 news |title= Vancouver sea otters a hit on YouTube |date=3 April 2007 |publisher= CBC News |access-date=15 January 2007 |url=http://www.cbc.ca/news/canada/british-columbia/vancouver-sea-otters-a-hit-on-youtube-1.688725}}</ref> Nyac died in September 2008, at the age of 20.<ref>{{cite web|url=http://www.vanaqua.org/pressroom/Nyac.html |title=Vancouver Aquarium's oldest sea otter, Nyac, passes|date=23 September 2008|publisher=[[Vancouver Aquarium]] |access-date=28 October 2008|archive-url=https://web.archive.org/web/20081120034407/http://www.vanaqua.org/pressroom/Nyac.html|archive-date=20 November 2008}}</ref> Milo, the darker one, died of lymphoma in January 2012.<ref>{{cite web|url=http://www.aquablog.ca/2012/01/beloved-sea-otter-milo/ |title=Beloved sea otter Milo|date=12 January 2012|publisher=[[Vancouver Aquarium]] |access-date=26 November 2014}}</ref> 

Other sea otters at the Vancouver Aquarium have also gone viral. During the [[2020 COVID-19 pandemic]], the livestream of Joey, a rescued sea otter pup at the Marine Mammal Rescue Center, attracted millions of viewers from across the world on YouTube and Twitch. Many viewers said the stream helped them cope with the anxiety and depression caused by the pandemic lockdowns.<ref>{{cite web |last1=Masters |first1=Tim |title=This adorable otter livestream took over Twitch's hot tub meta. Now, meet the people behind it |url=https://www.invenglobal.com/articles/14314/otter-twitch-stream-hot-tub-pools-beaches |website=Inven Global|date=18 June 2021 }}</ref> In June 2024, a video of another rescued sea otter pup, Tofino, received over 120,000,000 views and 5,000,000 likes on Instagram.<ref>{{cite web |title=Our vet staff, animal care team and some lovely volunteers will be working around the clock for months to ensure proper care of this new pup |url=https://www.instagram.com/nadinetrottier/reel/C8gE_0_RoUE/ |website=Instagram}}</ref><ref>{{cite web |title=Teeny tiny orphaned 5-week-old baby sea otter pup nursed to health by rescuers |url=https://www.goodmorningamerica.com/living/video/teeny-tiny-orphaned-5-week-baby-sea-otter-111591115 |website=Good Morning America}}</ref><ref>{{cite news |last1=Nassar |first1=Hana Mae |title=Vancouver Aquarium welcomes orphaned sea otter pups Tofino and Luna |url=https://vancouver.citynews.ca/2024/08/20/vancouver-aquarium-sea-otter-pups-2/ |agency=CityNews Vancouver |date=20 August 2024}}</ref>

Beginning in 2019, the streamer Douglas Wreden, popularly known as [[DougDoug]], has held charity streams for the [[Monterey Bay Aquarium]] to celebrate the birthday of [[Rosa (sea otter)|Rosa]] the sea otter.<ref>{{Cite web |title=Extraordinary birthday shell-ebrations for Rosa the sea otter |url=https://www.montereybayaquarium.org/stories/dougdoug-celebrate-rosa-sea-otter-birthday |url-status=live |archive-url=https://web.archive.org/web/20220525163615/https://www.montereybayaquarium.org/stories/dougdoug-celebrate-rosa-sea-otter-birthday |archive-date=May 25, 2022 |access-date=June 6, 2024 |website=www.montereybayaquarium.org}}</ref> As of 2024, DougDoug and his community have raised over $1,000,000 in Rosa's name.<ref>{{Cite web |title=our community raised... $625,375 FOR MONTEREY BAY, bringing the total to over ONE MILLION DOLLARS... |url=https://x.com/DougDougFood/status/1827974597599244590 |access-date=September 26, 2024 |website=X (formerly Twitter)}}</ref> 

=== Current conservation ===
Sea otters, being a known keystone species, need a humanitarian effort to be protected from endangerment through "unregulated human exploitation".<ref>{{cite book|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780128014028000044|doi=10.1016/B978-0-12-801402-8.00004-4 |chapter=Challenges to Sea Otter Recovery and Conservation |title=Sea Otter Conservation |year=2015 |last1=Ballachey |first1=Brenda E. |last2=Bodkin |first2=James L. |pages=63–96 |isbn=978-0-12-801402-8 }}</ref> This species has increasingly been impacted by the large oil spills and environmental degradation caused by overfishing and entanglement in fishing gear.<ref>{{cite book|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780128014028000044|doi=10.1016/B978-0-12-801402-8.00004-4 |chapter=Challenges to Sea Otter Recovery and Conservation |title=Sea Otter Conservation |year=2015 |last1=Ballachey |first1=Brenda E. |last2=Bodkin |first2=James L. |pages=63–96 |isbn=978-0-12-801402-8 }}</ref> Current efforts have been made in legislation: the international Fur Seal Treaty, The Endangered Species Act, IUCN/The World Conservation Union, Convention on international Trade in Endangered Species of Wild Fauna and Flora, and the Marine Mammal Protection Act of 1972. Other conservation efforts are done through reintroduction and zoological parks.

Sea Otter Awareness Week is held every year during the last full week of September. Zoos, aquariums, and other educational institutions hold events highlighting sea otters, their ecological importance, and the challenges facing their conservation. It is organized and sponsored by Defenders of Wildlife, the Monterey Bay Aquarium, the California Department of Parks and Recreation, Sea Otter Savvy, and the Elakha Alliance.<ref>{{cite web |title=Sea Otter Awareness Week |url=https://defenders.org/sea-otter-awareness-week |website=Defenders of Wildlife}}</ref><ref>{{cite web |title=Sea Otter Awareness Week |url=https://www.montereybayaquarium.org/animals/sea-otter-awareness-week |website=Monterey Bay Aquarium}}</ref>

==See also==
* [[California Fur Rush]]

==Notes==
{{NoteFoot}}

== References ==
=== Citations ===
{{Reflist|refs=
<ref name=Farris21>{{cite journal |ref=Farris|title=Mains'l Haul, a Journal of Pacific Maritime History, Vol 43|journal=Mains'l Haul |last=Farris |first=Glenn|year=2007|publisher=Maritime Museum of San Diego |location=San Diego, California| issn=1540-3386|page=21}}</ref>
<ref name="h1342">{{Cite book|ref=Heptner|last1=Heptner|first1=V. G.|last2=Sludskii|first2=A. A.|url=https://archive.org/details/mammalsofsov212001gept|title=Mammals of the Soviet Union. Vol. II, part 1b, Carnivores (Mustelidae and Procyonidae)|publisher=Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation|year=2002|isbn=978-90-04-08876-4|page=1342}}</ref>
<ref name=Mathes326>{{cite book|ref=Mathes |title=The Russian-Mexican Frontier |last=Mathes |first=Michael|year=2008|publisher=Fort Ross Interpretive Association, Inc.|page=326|location=Jenner, California|isbn=978-1-60643-951-7}}</ref>
}}

=== Cited works ===
<!-- An alphabetical listing of inline citations (previous section) should be listed here. -->
* {{cite book |ref=Kenyon| 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. | isbn=978-0-486-21346-0}}
* {{cite book|ref=Love |title= Sea Otters|last= Love|first=John A. |year= 1992|publisher=Fulcrum Publishing|location=Golden, Colorado |isbn=978-1-55591-123-2 |oclc= 25747993}}
* {{cite book |ref=Nickerson| title= Sea Otters, a Natural History and Guide | url= https://archive.org/details/seaottersnatural0000nick | url-access= registration | last=Nickerson |first=Roy|
year=1989|publisher=Chronicle Books|location=San Francisco, CA|isbn=978-0-87701-567-3 | oclc= 18414247}}
* {{cite book|ref=Silverstein |title= The Sea Otter|url= https://archive.org/details/seaotterendanger00alvi|url-access= registration|last= Silverstein |first= Alvin|author2=Silverstein, Virginia and Robert |year= 1995|publisher= The Millbrook Press, Inc. |location= Brookfield, Connecticut|isbn=978-1-56294-418-6 |oclc= 30436543}}
* {{cite book|ref=Middleton | work= California Academy of Science's Member Newsletter October/November 2001
 |title=Maritime Activities And Their Perception Today|last=Middleton |first=John |year=2001|publisher=California Academy of Science |location=San Francisco, California |issn=1531-2224}}
* {{cite book|ref=VanBlaricom|title=Sea Otters|year=2001|last=VanBlaricom|first=Glenn R.|publisher=Voyageur Press Inc.|location=Stillwater, MN|isbn=978-0-89658-562-1|oclc=46393741|url=https://archive.org/details/seaotters0000vanb}}
* {{cite book |ref=McLeish |title=Return of the Sea Otter: The Story of the Animal That Evaded Extinction on the Pacific Coast|author=McLeish, Todd |year=2018|publisher=Sasquatch Books|location=Seattle, WA |isbn=978-1-63217-137-5}}

== External links ==
{{Commons category|Enhydra lutris|<br/>Enhydra lutris<br/>(Sea otter)}}
{{Wikispecies|Enhydra lutris}}
* [https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180547 ''Enhydra lutris'' (Linnaeus, 1758)] at the [[Integrated Taxonomic Information System]]
* [http://www.marinespecies.org/aphia.php?p=taxdetails&id=242598 ''Enhydra lutris'' (Linnaeus, 1758)] at the [[World Register of Marine Species]]
* [http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1019&context=libraryscience ''De Bestiis Marinis, or, The Beasts of the Sea'' (1751)] ([[Portable Document Format|PDF]]), pp.&nbsp;68–82, transcribed field notes from 18th-century German zoologist [[Georg Wilhelm Steller]]
* [http://online.wr.usgs.gov/outreach/otter/ Precipice of Survival: The Southern Sea Otter] {{Webarchive|url=https://web.archive.org/web/20080422033215/http://online.wr.usgs.gov/outreach/otter/ |date=22 April 2008 }} ([[Adobe Flash]]), a 48-minute program on the southern sea otter's history by the [[United States Geological Survey]]
* [https://x.com/gmF65cxXrQN3jDd NPO Etopirika Kikin], Japanese non-profit posting frequent updates on the wild sea otters living along Cape Kiritappu in Hokkaido.

{{Carnivora|M.}}
{{Taxonbar |from=Q41407}}
{{Authority control}}
{{Portal bar|Marine life|Mammals|Animals|Biology}}

[[Category:Carnivorans of Asia]]
[[Category:Carnivorans of North America]]
[[Category:Endangered biota of Asia]]
[[Category:Endangered fauna of California]]
[[Category:Endangered fauna of North America]]
[[Category:Endangered fauna of the United States]]
[[Category:Extant Pleistocene first appearances]]
[[Category:Fauna of California]]
[[Category:Fauna of the Aleutian Islands]]
[[Category:Fauna of the Pacific Ocean]]
[[Category:Fur trade]]
[[Category:Fauna of the Kuril Islands]]
[[Category:Mammals described in 1758|sea otter]]
[[Category:Mammals of Canada]]
[[Category:Mammals of Russia]]
[[Category:Mammals of Mexico]]
[[Category:Mammals of Japan]]
[[Category:Mammals of the United States]]
[[Category:Marine mammals]]
[[Category:Otters|sea otter]]
[[Category:Pleistocene animals of North America]]
[[Category:Pleistocene carnivorans]]
[[Category:Quaternary mammals of Asia]]
[[Category:Quaternary mammals of North America]]
[[Category:Taxa named by Carl Linnaeus|sea otter]]
[[Category:Tool-using mammals]]
[[Category:Western North American coastal fauna]]
[[Category:Semiaquatic mammals]]
[[Category:Fauna of the Holarctic realm]]
[[Category:Apex predators]]
[[Category:Articles containing video clips]]
[[Category:Biota of the Temperate Northern Pacific]]
[[Category:Species that are or were threatened by human consumption]]