Distribution of Enhydra lutris in British Columbia. (Click on the map to view a larger version.)
Source: Map courtesy of the Province of British Columbia (2008).
The Sea Otter is a globally endangered species of marine mammal in the Weasel Family (IUCN 2011, Wikipedia 2011). It is our smallest marine mammal. Males can reach lengths of 148 cm and weigh from 14 - 45 kg, females are smaller. Sea Otters have a very thick, insulating, coat of fur.
"The Sea Otter has the thickest fur of any living animal, with an
incredible 100 000 or more hairs per square centimetre." (Blood 1993).
Sea Otters have low reproductive rates (Blood 1993). Female Sea Otters breed at four years old and have one pup every one to two years, usually in the spring or early summer (Blood 1993). Pups nurse for the first month, and begin to dive in their second month (Blood 1993).
Sea Otters feed mainly on marine invertebrates, including sea urchins, bivalves, and crustaceans (IUCN 2011).
Sea Otters are well-known for their tool-using abilities, and are the only mammal other than primates to use tools (Blood 1993). They use rocks to open shells while floating in the water. Blood (1993) says: "Their rock tools range from 6 to 15 cm across, and favourite rocks may be carried in the armpit pouch on several successive dives."
Sea otters are often seen feeding or resting in social groups. "Groups of the sociable Sea Otter
are called rafts, and usually
consist entirely of females and
pups or of males. Male rafts are usually larger (up to 100 or more in Alaska); but female rafts may contain up to 40 adults with their
pups." (Blood 1993).
Sea Otters rarely go ashore (Blood 1993), and are found in a variety of near shore marine environments, with preference for sheltered rocky coastlines where they forage most frequently in water less than 30m deep, less than one km from shore (IUCN 2011). Although they are found in other habitat types, the typical habitat for this species is rocky substrates supporting kelp beds, where the kelp canopy is used for foraging and resting (IUCN 2011). They require unpolluted water (Blood 1993).
Historically, the Sea Otter was found across the North Pacific, from Japan to peninsular and south coastal Alaska and south to Baja California, Mexico (Kenyon 1969). (IUCN 2011). However, as a result of commercial harvesting this species was almost extirpated throughout its entire range. Today, with reintroductions, populations are found from the Aleutian Islands in Alaska south to California, but with gaps in its distribution where populations have not recovered (IUCN 2011).
Distribution in British Columbia
In British Columbia, Sea Otters were reintroduced following extirpation by the fur trade. "Between 1969 and 1972, 89 Sea Otters were flown or shipped from Alaska to the west coast of Vancouver Island, British Columbia. They established a healthy population, estimated to be over 3,000 as of 2004, and their range is now from Tofino to Cape Scott. In 1989, a separate colony was discovered in the central British Columbia coast. It is not known if this colony, which had a size of about 300 animals in 2004, was founded by transplanted otters or by survivors of the fur trade." (IUCN 2011).
"Three regional subspecies have been confirmed by Cronin et al. (1996); Enhydra lutris lutris (Linnaeus, 1758) from the Asian range of the Kuril Islands southeast to the Kamchatka Peninsula and the Commander Islands, E. l. kenyoni from the Aleutian Islands to Prince William Sound, Alaska, USA, along the Pacific coast of Canada and into Oregon state in the continental USA, and E. l. nereis (Merriam, 1904) from central California, USA." (IUCN 2011).
The Sea Otter is considered globally endangered and vulnerable to large-scale population declines; it is believed to have undergone a decline in numbers exceeding 50% over the past 30 years (approximately three generations). (IUCN 2011). Sea Otters suffered dramatic declines historically, to near extirpation, because of commercial harvesting with approximately 2000 animals surviving by the end of the fur trade in 1911 ((IUCN 2011). The species recovered from 11 small, widely dispersed, remnant populations found in Russia and the US, however, by the 1980s, population surveys indicated that populations are not thriving or are in decline, a result of a combination of factors (oil spills, predation, disease and probably fisheries operations); there are significant population declines in Alaska and a small population in California is not thriving (IUCN 2011). Killer whale predation in Alaska is significant, and mortality from disease is significant in California populations.
The IUCN (2011) provides the following summary of the species: "In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). Although it appears that harvests periodically led to local reductions of Sea Otters (Simenstad et al. 1978), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969). Remnant populations were located in the Kuril Islands, Kamchatka and in the Commander Islands Russia; five in Southwestern Alaska (the Aleutian Islands, Alaska Peninsula, and Kodiak Island), and one remnant population in each of the following regions; Southcentral Alaska (Prince William Sound), Canada (Queen Charlotte Islands), central California, and Mexico (San Benito Islands) (Estes 1980). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations have presumably died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969)."
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2020-05-30 12:47:10 PM]
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