Animal Diversity Web

Ge­o­graphic Range

Sea ot­ters, En­hy­dra lutris, are found in two ge­o­graphic re­gions on the Pa­cific Coast: along the Kuril and Com­man­der Is­lands off the coast of Rus­sia, the Aleut­ian Is­lands below the Bering Sea, and the coastal wa­ters off the Alaskan Penin­sula to Van­cou­ver Is­land, Canada; and along the cen­tral Cal­i­for­nia coast from Ano Nuevo to Point Sur.

Sea ice lim­its their north­ern range to below 57 de­grees N lat­ti­tude, and the dis­tri­b­u­tion of kelp forests lim­its the south­ern range to about 22 de­grees N lat­ti­tude. Hunt­ing dur­ing the 18th and 19th cen­turies greatly re­duced the dis­tri­b­u­tion of sea ot­ters.

Three sub­species of E. lutris are rec­og­nized today. En­hy­dra lutris lutris ranges from the Kuril Is­lands north to the com­man­der is­lands in the west­ern pa­cific. En­hy­dra lutris nereis is found off the coast of cen­tral Cal­i­for­nia. En­hy­dra lutris keny­oni is dis­trib­uted through­out the Aleut­ian Is­lands and south­ern Alaska, and has been rein­tro­duced to var­i­ous lo­ca­tions from south of Prince William Sound, Alaska to Ore­gon. (Estes, 1980; Lock­wood, 2006; Nowak, 1999; Wil­son, et al., 1991)

• Biogeographic Regions
• nearctic
  • native
• pacific ocean
  • native

Habi­tat

Sea ot­ters in­habit tem­per­ate coastal wa­ters with rocky or soft sed­i­ment ocean bot­tom. They live in off­shore forests of giant kelp (Macro­cys­tis pyrifera), and spend most of their ac­tive time for­ag­ing below the canopy. They eat, rest, and groom them­selves at the water sur­face. While sea ot­ters are ca­pa­ble of div­ing to depths of at least 45 me­ters, they pre­fer coastal wa­ters up to 30 me­ters deep. The shal­lower the water, the less time is spent div­ing to reach food. (Estes, 1980; Nowak, 1999; Paine, 1993)

• Habitat Regions
• temperate
• saltwater or marine

• Aquatic Biomes
• coastal

• Other Habitat Features
• intertidal or littoral

• Range depth

  45 to 0 m

  147.64 to 0.00 ft

Phys­i­cal De­scrip­tion

Alaskan sea ot­ters are slightly larger than Cal­i­forn­ian ot­ters. Adult male Alaskan ot­ters weigh 27 to 39 kg, while fe­males weigh 16 to 27 kg. Adult male Cal­i­for­nia sea ot­ters av­er­age 29 kg in mass, while fe­males av­er­age 20 kg. In­di­vid­u­als can weigh as much as 45 kg. Males mea­sure 1.2 to 1.5 m in length, while fe­males mea­sure 1 to 1.4 m. The tail com­prises less than a third of the body length, mea­sur­ing 25 to 35 cm.

The pelage is brown or red­dish brown. The fur con­sists of two lay­ers: a dark un­der­coat and longer, lighter-col­ored guard hairs, which trap a layer of air next to the skin to keep it dry. Sea otter fur is the dens­est of all mam­mals, with about 100,000 hairs per square cen­time­ter. Be­cause sea ot­ters do not have any in­su­lat­ing fat, the fur is re­spon­si­ble for heat main­te­nance.

Sea ot­ters have cir­cu­lar, furry faces with short noses, rounded eyes and ears, and long whiskers that as­sist in for­ag­ing for food. The hind legs are long and the paws are broad, flat and webbed. The fore­limbs are short and have re­tractable claws, which help with groom­ing and eat­ing. Sea ot­ters have patches of loose skin under the fore­arms that they use to help store tools (usu­ally a rock) so they can have free “hands” while eat­ing, and to trans­port food dur­ing div­ing. Sea ot­ters are the only car­ni­vores with just 4 lower in­cisors. Fe­males have two mam­mae. (Estes, 1980; Nowak, 1999; Paine, 1993; Sea­World Parks & En­ter­tain­ment, 2011)

• Other Physical Features
• endothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger

• Range mass

  14 to 45 kg

  30.84 to 99.12 lb

• Range length

  1 to 1.5 m

  3.28 to 4.92 ft

• Average basal metabolic rate

  98.479 W

  AnAge

Re­pro­duc­tion

Sea ot­ters are polyg­y­nous, with males hav­ing mul­ti­ple fe­male part­ners through­out the year. Many males ac­tively de­fend ter­ri­to­ries. Dis­putes are usu­ally set­tled with splash­ing and vocal dis­plays, and fight­ing is rare. Males mate with fe­males 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. (Estes, 1980; Mc­Shane, et al., 1995; Nowak, 1999; Ocean­Link, 2011; Sea­World Parks & En­ter­tain­ment, 2011)

• Mating System
• polygynous

Sea ot­ters can re­pro­duce year round. There are peaks of birth in May to June in the Aleut­ian Is­lands and in Jan­u­ary to March in Cal­i­for­nia. Sea ot­ters are one of sev­eral species of mam­mals that un­dergo de­layed im­plan­ta­tion in which the em­bryo does not im­plant dur­ing the im­me­di­ate pe­riod fol­low­ing fer­til­iza­tion, but re­mains in a state of sus­pended growth al­low­ing for birth to occur under fa­vor­able con­di­tions. De­layed im­plan­ta­tion pro­duces var­ied ges­ta­tion times, which has been re­ported as 4 to 12 months. Fe­males usu­ally give birth about once a year, though many fe­males ex­pe­ri­ence longer breed­ing in­ter­vals, giv­ing birth every 2 years. If a pup does not sur­vive, the mother may ex­pe­ri­ence post­par­tum es­trus.

Ori­en­ta­tion of the fetus may be ei­ther cau­dal or cephalic, al­though cephalic ori­en­ta­tion is more com­mon near birth. A sin­gle pup is born weigh­ing 1.4 to 2.3 kg. Twins occur in 2% of births, but only one pup can be raised suc­cess­fully. Pups typ­i­cally re­main with their mother for 5 to 6 months after birth. Fe­males reach sex­ual ma­tu­rity at 4 years of age. Males reach sex­ual ma­tu­rity at 5 to 6 years, but may not mate until much later. (Estes, 1980; Mc­Shane, et al., 1995; Nowak, 1999; Ocean­Link, 2011; Ried­man, et al., 1994; Sea­World Parks & En­ter­tain­ment, 2011)

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous
• delayed implantation
• post-partum estrous

• Breeding interval

  Sea otters breed once every 1 or 2 years.

• Breeding season

  Sea otters breed year round.

• Range number of offspring

  1 to 2

• Average number of offspring

  1

• Average number of offspring

  1

  AnAge

• Range gestation period

  4 to 12 months

• Average gestation period

  6 months

• Average weaning age

  6 months

• Range age at sexual or reproductive maturity (female)

  4 to 5 years

• Range age at sexual or reproductive maturity (male)

  5 to 8 years

• Average age at sexual or reproductive maturity (male)

  6 years

Male sea ot­ters do not pro­vide any care to their off­spring. Pups are weaned at around 6 months of age but start to eat solid foods shortly after birth. Fe­males carry their pups on their bel­lies while they nurse. Their milk is 20 to 25% fat. While a mother is for­ag­ing, she wraps her pup in kelp at the water sur­face to keep it from drift­ing away. At any sign of a preda­tor, the fe­male clamps onto her pup’s neck with her mouth and dives. Fe­males groom their pups ex­ten­sively for 3 months as their coat de­vel­ops. A pup’s coat traps air, which keeps the an­i­mal afloat. Pups start div­ing at 2 months of age. The pup re­mains de­pen­dent on the mother for about 6 to 8 months. (Lock­wood, 2006; Paine, 1993; Sea­World Parks & En­ter­tain­ment, 2011)

• Parental Investment
• female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• post-independence association with parents

Lifes­pan/Longevity

The max­i­mum es­ti­mated lifes­pan of sea ot­ters is 23 years in the wild. (Nowak, 1999)

• Typical lifespan
  Status: wild

  23 (high) years

• Average lifespan
  Sex: male
  Status: captivity

  19.0 years

  Max Planck Institute for Demographic Research

Be­hav­ior

Sea ot­ters con­gre­gate in groups known as rafts or pods when rest­ing. Fe­males tend to avoid males ex­cept when mat­ing. Sea ot­ters are long-lived and typ­i­cally re­main in the same area for years. They spend the ma­jor­ity of their time in the ocean, but rest on land when the pop­u­la­tion den­sity is high or dur­ing stormy weather.

Sea ot­ters uti­lize ver­ti­cal un­du­la­tions of the body to swim, tuck­ing in the fore­limbs and using the hind limbs and tail to con­trol their mo­tion. Ot­ters can swim as fast as 9 km per hour under water. Sea ot­ters are di­ur­nal with cre­pus­cu­lar peaks in for­ag­ing ac­tiv­ity. For­ag­ing dives usu­ally last 50 to 90 sec­onds, but ot­ters can re­main sub­merged for nearly 6 min­utes. Sea ot­ters spend 15 to 55% of their time for­ag­ing, de­pend­ing on food avail­abil­ity.

When rest­ing or sleep­ing, sea ot­ters float on their back and wrap them­selves in kelp to keep from drift­ing. Their hind limbs stick out of the water and their fore­limbs are ei­ther folded on their chest or used to cover their eyes. They dili­gently groom and clean their fur to main­tain its in­su­lat­ing abil­ity. Sea ot­ters are one of few mam­mals that ex­hibit tool use. (Cohn, 1998; Estes, 1980; Estes, et al., 1986; Fisher, 1939; Lim­baugh, 1961; Nowak, 1999; Paine, 1993)

• Key Behaviors
• natatorial
• diurnal
• crepuscular
• motile
• sedentary
• solitary
• territorial
• social

Home Range

Male sea ot­ters have larger home ranges than fe­males. The home range of a male may over­lap with that of sev­eral fe­males. Same-sex ter­ri­to­ries do not over­lap and are de­fended by their own­ers. (Sea­World Parks & En­ter­tain­ment, 2011)

Com­mu­ni­ca­tion and Per­cep­tion

Sea ot­ters com­mu­ni­cate through body con­tact and vo­cal­iza­tions, al­though they are not overly vocal. Re­searchers have rec­og­nized nine vo­cal­iza­tions. Pups use squeals to com­mu­ni­cate with their moth­ers. Other calls in­clude coos, whines, dis­tress screams, growls, snarls, and whis­tles. Scent is im­por­tant in recog­ni­tion and sur­vey­ing phys­i­o­log­i­cal states. Each sea otter has its own dis­tinct scent that con­veys iden­tity, age, and sex. (Sea­World Parks & En­ter­tain­ment, 2011)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Sea ot­ters are car­niv­o­rous. They will eat nearly any fish or ma­rine in­ver­te­brate they can find in their kelp for­est for­ag­ing grounds. Their diet con­sists of ma­rine in­ver­te­brate her­bi­vores and fil­ter feed­ers such as sea urchins (Strongy­lo­cen­tro­tus pur­pu­ra­tus and Strongy­lo­cen­tro­tus fran­cis­canus), sea stars (Pisas­ter ochraceus), limpets (Diodora as­pera), coast mus­sels (Mytilus edulis), chi­tons (Katha­rina tu­ni­cata), and pur­ple-hinged rock scal­lops (Cras­sadoma gi­gan­tea). Ot­ters also eat crabs, oc­to­pus, squid, and fish. In­di­vid­u­als tend to be spe­cial­ized in their choice of prey; one otter may con­sume only urchins and crabs while an­other may eat mostly fish, de­pend­ing on the abil­i­ties of the in­di­vid­ual and local food avail­abil­ity. Ot­ters con­sume 20 to 25% of their body weight each day. They ob­tain most of their water from prey but also drink sea­wa­ter to sat­isfy thirst. (Cohn, 1998; Estes, 1980; Estes, et al., 1986; Lim­baugh, 1961; Nowak, 1999; Paine, 1993; Sea­World Parks & En­ter­tain­ment, 2011)

Sea ot­ters com­monly feed in small groups. Hunt­ing oc­curs on the sea floor. They use their sen­si­tive whiskers to lo­cate small crea­tures in the dense kelp beds and crevices. They use their small, agile forepaws to cap­ture prey and to rub, roll, twist, and pull apart prey. Sea ot­ters col­lect in­ver­te­brates in loose folds of skin under their armpits and eat at the sur­face. The feed­ing process, in­clud­ing for­ag­ing, eat­ing, and clean­ing their fur after a meal, lasts 2 to 3 hours. Sea ot­ters usu­ally eat 3 to 4 times a day.

Sea ot­ters break open prey items with hard shells or ex­oskele­tons with a rock. Some ot­ters hold the rock on their chest and drive the prey into the rocks. Oth­ers leave the prey on their chests and hit the prey with the rocks. The same rock is kept for many dives. Ot­ters often wash their prey by hold­ing it against their body and turn­ing in the water. Males steal from fe­males if they get a chance. For this rea­son, fe­males tend to for­age in sep­a­rate areas. (Cohn, 1998; Estes, 1980; Estes, et al., 1986; Fisher, 1939; Lim­baugh, 1961; Nowak, 1999; Paine, 1993; Sea­World Parks & En­ter­tain­ment, 2011)

• Primary Diet
• carnivore
  • piscivore
  • eats non-insect arthropods
  • molluscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• echinoderms
• other marine invertebrates

Pre­da­tion

Great white sharks (Car­char­o­don car­charias) are one of the pri­mary preda­tors of sea ot­ters. Ot­ters are oc­ca­sion­ally eaten by coy­otes (Canis lantrans) after tak­ing refuge on the sand dur­ing stormy weather. Young pups left alone on the sur­face while their moth­ers feed be­neath the sur­face are preyed upon by bald ea­gles (Hali­aee­tus leu­co­cephalus). It was once thought that killer whales Or­ci­nus orca were re­spon­si­ble for de­clines in the sea otter pop­u­la­tion in Alaska, but ev­i­dence is in­con­clu­sive. (Estes, 1980; Estes, et al., 1998; Kuker and Bar­rett-Lennard, 2010; Lim­baugh, 1961; Mc­Shane, et al., 1995)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • Coyotes Canis lantrans
  • Great white sharks Carcharadon charcarias
  • Bald eagles Haliaeetus leucocephalus
  • Killer whales Orcinus orca
  • California sea lions Zalophus californianus
  • Humans Homo sapiens

Ecosys­tem Roles

Sea ot­ters are vital to the over­all health and di­ver­sity of the kelp for­est ecosys­tem. They are con­sid­ered a key­stone species and play a major role in the com­mu­nity by con­trol­ling her­biv­o­rous in­ver­te­brates. Sea ot­ters prey on sea urchins, thereby pre­vent­ing sea urchins from over­graz­ing the kelp for­est. This al­lows the kelp for­est to thrive and con­tributes to an in­crease in ma­rine di­ver­sity. The va­ri­ety in the sea otter diet re­duces com­pe­ti­tion be­tween ben­thic graz­ers and sup­ports greater di­ver­sity in those species. The pres­ence of sea ot­ters is be­lieved to be im­por­tant in the evo­lu­tion of kelp for­est ecosys­tems.

Two api­com­plexan pro­to­zoan par­a­sites, Sar­cosys­tis neu­rona and Tox­o­plasma gondii in­fect the sea otter caus­ing en­cephali­tis. An acan­tho­cephalen worm (Pro­fil­i­col­lis) has also been linked to mor­tal­ity and de­cline in the pop­u­la­tion. (Cohn, 1998; Estes and Dug­gins, 1995; Estes and Palmisano, 1974; Estes, 1980; Estes, et al., 1978; Jes­sup, et al., 2004)

• Ecosystem Impact
• keystone species

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

The fur of sea ot­ters was of great im­por­tance in the fur trade from the mid 1700s to 1911. Their fur was cov­eted due to its ex­treme den­sity and in­su­lat­ing qual­ity. Pelts sold for as much as $1,125 each and were fash­ioned into hats, coats, and other gar­ments sold in Rus­sia, Canada, and the United States. (Cray, 2006; Nowak, 1999)

• Positive Impacts
• body parts are source of valuable material

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Sea ot­ters feed on shell­fish, sea urchins, and crabs, com­pet­ing with com­mer­cial fish­eries. (Nowak, 1999)

Con­ser­va­tion Sta­tus

Sea ot­ters were hunted to near ex­tinc­tion (1000 to 2000 in­di­vid­u­als world­wide) at until the turn of the 20th cen­tury when the United States, Rus­sia, Japan, and Great Britain reached an agree­ment in 1911 called the In­ter­na­tional Fur Seal Treaty, ban­ning the hunt­ing of fur-bear­ing sea mam­mals. In 1972, the U.S. Ma­rine Mam­mal Pro­tec­tion Act of­fered fur­ther pro­tec­tion by ban­ning cap­ture and ha­rass­ment of sea mam­mals. The Exxon Valdez oil spill of 1989 had a dra­matic ef­fect on the Alaskan sea otter pop­u­la­tion, killing ap­prox­i­mately 5,000 in­di­vid­u­als.

Par­a­sites and in­fec­tious dis­ease con­tribute to sea otter mor­tal­ity, specif­i­cally Tox­o­plasma gondii, which in­fects do­mes­tic cats, and Sar­cosys­tis neu­rona, which in­fects opos­sums. It is pos­tu­lated that cat and opos­sum feces travel to storm drains via runoff and dis­posal in toi­lets, even­tu­ally com­ing into con­tact with sea ot­ters. In Sep­tem­ber 2006, Gov­er­nor Arnold Schwarzeneg­ger passed a law rais­ing the max­i­mum fine for harm­ing a sea otter to $25,000, and re­quired that all cat lit­ter sold in Cal­i­for­nia dis­play a warn­ing label that ad­vises not to dump cat feces down storm drains or in toi­lets.

Ac­cord­ing to the Otter Foun­da­tion, the Cal­i­for­nia sea otter pop­u­la­tion de­clined from July 2008 to July 2011. Es­ti­mates sug­gest a Cal­i­for­nia pop­u­la­tion of ap­prox­i­mately 2700 in­di­vid­u­als. En­hy­dra lutris was placed under the En­dan­gered Species Act (ESA) in 1973 and is now listed on CITES Ap­pen­dix I and II. In Canada, sea ot­ters are pro­tected under the Species at Risk Act. As of 2008, E. lutris is con­sid­ered en­dan­gered by the IUCN. Sea ot­ters are vul­ner­a­ble to large-scale pop­u­la­tion de­clines, with oil spills being the great­est an­thro­pogenic threat. (Cohn, 1998; Cray, 2006; Do­roff and Bur­din, 2011; Hilton-Tay­lor, 2000; Jes­sup, et al., 2004; Nowak, 1999)

• IUCN Red List

  Endangered
  More information

• IUCN Red List

  Endangered
  More information

• US Federal List

  Threatened

• CITES

  Appendix I Appendix II

• State of Michigan List

  No special status

Con­trib­u­tors

Joe Al­le­gra (au­thor), San Diego Mesa Col­lege, Rhi­an­non Rath (au­thor), San Diego Mesa Col­lege, Aren Gun­der­son (au­thor), Uni­ver­sity of North­ern Iowa, Paul De­twiler (ed­i­tor), San Diego Mesa Col­lege, Gail Mc­Cormick (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Ref­er­ences

Cohn, J. 1998. Un­der­stand­ing Sea Ot­ters. Bio­Science, 48: 151-155.

Cray, D. 2006. What's Killing the Sea Ot­ters. Time: 62-63. Ac­cessed Sep­tem­ber 25, 2012 at http://​www.​time.​com/​time/​magazine/​article/​0,9171,1538645,00.​html.

Do­roff, A., A. Bur­din. 2011. "En­hy­dra lutris" (On-line). In: IUCN 2012. IUCN Red List of Threat­ened Species. Ver­sion 2012.1. Ac­cessed No­vem­ber 12, 2011 at http://​www.​iucnredlist.​org/​details/​7750/​0.

Estes, J. 1980. En­hy­dra lutris. Mam­malian Species, 133: 1-8.

Estes, J., D. Dug­gins. 1995. Sea ot­ters and kelp forests in Alaska: gen­er­al­ity and vari­a­tion in a com­muntiy eco­log­i­cal par­a­digm. Eco­log­i­cal Mono­graphs, 65: 75-100.

Estes, J., J. Palmisano. 1974. Sea ot­ters: their role in struc­tur­ing nearshore com­mu­ni­ties. Sci­ence, 185: 1058-1060.

Estes, J., N. Smith, J. Palmisano. 1978. Sea otter pre­da­tion and com­mu­nity or­ga­ni­za­tion in the west­ern Aleut­ian Is­lands, Alaska. Ecol­ogy, 59: 822-833.

Estes, J., M. Tin­ker, D. Doak. 1998. Killer whale pre­da­tion on sea ot­ters link­ing oceanic and nearshore ecosys­tems. Sci­ence, 282: 473-476.

Estes, J., K. Un­der­wood, M. Kar­mann. 1986. Ac­tiv­ity-time bud­gets of sea ot­ters in Cal­i­for­nia. Jour­nal of Wildlife Man­age­ment, 50: 626-636.

Fisher, E. 1939. Habits of the south­ern sea otter. Jour­nal of Mam­mal­ogy, 50: 21-36.

Hilton-Tay­lor, C. 2000. "En­hy­dra lutris" (On-line). In: IUCN 2000. IUCN Red List of Threat­ened Species. Ver­sion 2000.1. Ac­cessed De­cem­ber 05, 2001 at http://​www.​redlist.​org/​search/​details.​php?​species=7750.

Jes­sup, D., M. Har­ris, C. Kreuder, J. Ames, P. Con­rad, M. Miller. 2004. South­ern Sea Otter as a Sen­tinel of Ma­rine Ecosys­tem Health. Eco­Health, 1(3): 239-245.

Kuker, K., L. Bar­rett-Lennard. 2010. A re-eval­u­a­tion of the role of killer whales Or­ci­nus orca in a pop­u­la­tion de­cline of sea ot­ters En­hy­dra lutris in the Aleut­ian Is­lands and a re­view of al­ter­na­tive hy­pothe­ses. Mam­mal Re­view, 40(2): 103-24.

Lim­baugh, C. 1961. Ob­ser­va­tions on the Cal­i­for­nia sea otter. Jour­nal of Mam­mal­ogy, 42: 271-273.

Lock­wood, S. 2006. Sea Ot­ters. Min­nesota: Chan­has­sen.

Mc­Shane, L., J. Estes, M. Ried­man, M. Staedler. 1995. Reper­tiore, struc­ture, and in­di­vid­ual vari­a­tion of vo­cal­iza­tions in the sea otter. Jour­nal of Mam­mal­ogy, 76: 414-427.

Nowak, R. 1999. Walker's Mam­mals of the World. Bal­ti­more and Lon­don: John Hop­kin's Uni­ver­sity Press.

Ocean­Link, 2011. "Sea Ot­ters" (On-line). Ocean­Link - Ma­rine Sci­ences Ed­u­ca­tion and Fun. Ac­cessed De­cem­ber 01, 2011 at http://​www.​oceanlink.​info/​biodiversity/​otter/​otter.​html.

Paine, S. 1993. The World of the Sea Otter. San Fran­cisco: Sierra Club.

Ried­man, M., J. Estes, M. Staedler, A. Giles, D. Carl­son. 1994. Breed­ing Pat­terns and re­pro­duc­tive suc­cess of Cal­i­for­nia sea ot­ters. Jour­nal of Wildlife Man­age­ment, 58: 391-399.

Sea­World Parks & En­ter­tain­ment, 2011. "Ot­ters" (On-line). Sea­World/Busch Gar­dens AN­I­MALS. Ac­cessed No­vem­ber 15, 2011 at http://​www.​seaworld.​org/​animal-info/​info-books/​otters/​index.​htm.

Wil­son, D., M. Bogan, R. Brownell, Jr., A. Bur­din, M. Maminov. 1991. Ge­o­graphic vari­a­tion in sea ot­ters, En­hy­dra lutris. Jour­nal of Mam­mal­ogy, 72: 22-36.