Enhydra lutris (Linnaeus, 1758)
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publication ID |
https://doi.org/ 10.5281/zenodo.5714044 |
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DOI |
https://doi.org/10.5281/zenodo.5714113 |
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persistent identifier |
https://treatment.plazi.org/id/038F87D4-CA48-FFA6-CFF0-3DA4FD9DF9CC |
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treatment provided by |
Conny |
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scientific name |
Enhydra lutris |
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Sea Otter
French: Loutre de mer / German: Meerotter / Spanish: Nutria marina
Taxonomy. Mustela lutris Linnaeus, 1758 View in CoL ,
Kamchatka, Russia.
Three subspecies are recognized.
Subspecies and Distribution.
E. l. lutris Linnaeus, 1758 — NE Russia (Commander Is, Kamchatka, Kurile Is & Sakhalin I).
E. l. kenyoni Wilson, 1991 — Aleutian Is through Alaska and W Canada (Vancouver I) to W USA (Washington).
E. l. nereis Merriam, 1904 — USA (California). View Figure
Descriptive notes. Head-body 100-120 cm, tail 25-37 cm; weight 21-45 kg (males), 14-33 kg (females). The Sea Otter is one of the largest species within the Mustelidae . Sea Otters have long bodies and short limbs. The pelage is reddish-brown to dark brown, with a gray or creamy-colored head, throat, and chest. The underfur is very dense, averaging 100,000 hairs per cm®. The head is wide and blunt, with long and thick vibrissae on the upper lips. The ears are small and set low to the sides, and capable of closing when the otter dives. The tail is slightly flattened dorso-ventrally, but uniform in thickness from the base to tip. All four feet are webbed and clawed. There is one pair of mammae. A fold of skin in the armpits enables the Sea Otter to transport prey at sea while foraging. The Sea Otter lacks anal glands. The skull is flat, broad and strong. Dental formula: 1 3/2, C 1/1, P 3/3, M 1/2 = 32. The molars are broad and flat, with rounded crowns. This is the only carnivore species with four (instead ofsix) lowerincisors.
Habitat. Sea Otters are found in coastal marine habitats from sheltered and sandy bays to rocky shorelines exposed to rough seas. Although marine mammals, they rarely venture more than one km from shore. Typically, they live and forage in waters at depths of up to 100 m, but the highest densities of Sea Otters occur in waters less than 40 m deep.
Food and Feeding. The diet is mostly marine invertebrates such as abalones, sea urchins, crabs, and molluscs. Other prey include squid, octopus, chitons, tubeworms, scallops, and, very occasionally, fish. In the northern Kodiak Archipelago, clams were the most frequently identified prey (57-67%, mostly Saxidomus giganteus); mussels (Mytilus sp.), crabs (primarily Telmessus sp.), and green sea urchins (Strongylocentrotus droebachiensis) contributed 25% to the diet. On the north side of the Alaska Peninsula, the dominant prey species in 50 spraints were mussels (Mytilus edulis), followed by three species of clams (Siliqua sp., Spisula polynyma, and Tellina lutea), sand dollars (Echinarachnius parma), and helmet crabs (Telmessus cheiragonus). In south-east Alaska, butter clams (S. giganteus) are the major prey items. Sea Otters on the outer coast of Washington feed heavily on bivalves (63%) and have a diverse diet consisting of several prey groups. In contrast, Sea Otters in the Strait ofJuan de Fuca have a restricted diet dominated by more than 60% red urchins (Strongylocentrotus franciscanus), with only two other prey species comprising more than 10% of their diet. Sea Otters forage in both rocky and soft-sediment areas on or near the ocean floor. They have good underwater vision and most prey is captured by sight. Prey hiding under rocks or in crevices may also be captured by feeling with the forefeet. Underwater dives are sustained by lungs that are 2-3 times larger than those of similarsized terrestrial mammals. Most hunting dives last 50-90 seconds. In coastal Washington, the average dive time was 55 seconds and average surface time was 45 seconds, irrespective of dive success. At least 77% of all dives were successful in capturing prey. Prey capture success was significantly lower for subadults (63%) than adults (82%). Sea Otters break the exoskeleton of large or hard-shelled prey by hitting the prey item on a rock carried by the otter on its belly. Sea Otters face a tremendous thermoregulatory challenge because of their constant life at sea. When in water, buoyancy and insulation are provided by their fur and the air bubbles trapped within it. The integrity of their pelage is thus essential to thermoregulation. Their metabolic heat production is 2-3 times greater than that of similar-sized terrestrial mammals. To sustain such heat production requires that Sea Otters consume 20-33% of their body mass in food daily. Sea Otters can drink seawater, and their kidneys produce very concentrated urine to avoid unnecessary water loss.
Activity patterns. Generally diurnal, with peaks in activity at dawn and dusk. Daytime foraging increases when females care for young. In Prince William Sound, Alaska, more time was spent foraging (30%) than on any other activity, and foraging bouts were longer than all other activities. Sea Otters rest by floating belly-up in the water with their feet out of the water. They sometimes rest on rocks near the water and often spend the night in a kelp bed, lying under strands of kelp to avoid drifting while sleeping. Ten vocalizations have been described for Sea Otters including screams of distress (heard especially when mothers and young are separated) and coos (heard mostly when individuals are content or in familiar company).
Movements, Home range and Social organization. Sea Otters can spend their entire life at sea, and their movements on land are awkward. In the water, they are graceful and can move at speeds of 1- 1-5 km /h at the surface and up to 9 km /h underwater. Annual total movements of both sexes frequently cover 50-100 km. Sea Otters are basically solitary, but they sometimes rest in concentrations of up to 2000 individuals, and groups may occur at feeding areas. They aggregate by sex and age, with males and females occupying separate sections of coastline. During the breeding season, some males move into the areas occupied by females and establish territories. Male territories are usually about 20-50 ha; female home ranges may be twice as large. These territories typically are located in prime feeding or resting areas, locations that are attractive to breeding females. The boundaries are vigorously patrolled and intruding males are repulsed, but serious fighting is rare. The ownerofa territory seeks to mate with any female that enters, though sometimes a pair bond is formed for a few days or weeks.
Breeding. Sea Otters are polygynous: males may mate with more than one female during the season. Mating and births occur throughout the year, but parturition peaks are in May and June in the Aleutians and from January to March off the coast of California. Implantation of the fertilized eggs into the uterus is delayed, and total gestation lasts from 4-12 months. Births occur in water. Litter size is one, very rarely two. At birth, neonates weigh 1.4-2.3 kg. The female swims on her back and nurses with the young on her chest. Young Sea Otters may take some solid food shortly after birth, but may nurse until they are almost adult size. The period of dependency on the mother is thought to be about five to eight months. Offspring start diving after two months. Sexual maturity is reached at four years of age. Most females do not have young every year, although some females are capable of annual reproduction. Males may begin mating at five orsix years, but usually do not become active breeders until several more years have passed.
Status and Conservation. CITES Appendix I and II. Classified as Endangered in The IUCN Red List. Sea Otters are hunted for their fur, which has led to a large reduction in local populations and their distribution. Extirpated in Japan (coastal Hokkaido) and Mexico (Baja California), but now translocations have now reestablised Sea Otters in south-east Alaska, south-west Canada (Vancouver I), and north-west USA (Washington and Oregon). They are legally harvested in Alaska, with the annual harvest slightly exceeding 1000 animals. Sea Otters are also persecuted as perceived competitors for shellfish. In the last few decades, massive oil spills, such as that of the Exxon Valdez in 1989, have also decimated Sea Otter populations.
Bibliography. Bodkin (2003), Doroff & DeGange (1994), Estes (1980), Estes & Palmisano (1974), Gentry & Peterson (1967), Green & Brueggeman (1991), Hall & Schaller (1964), Hattori et al. (2005), IUCN (2008), Kenyon (1969), Pearson & Davis (2005), Pearson et al. (2006), Sandegren et al. (1973), Shimek & Monk (1977), Wilson et al. (1991), Wozencraft (2005).
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