Facts About Southern Sea Otters
RANGE: Sea otters (Enhydra lutris) once ranged along the Pacific Rim from Japan to Baja California, numbering 150,000 to 300,000 animals. Fur traders seeking their lush pelts hunted them to the brink of extinction in the 18th and 19th centuries. Sea otters now range from Alaska to California’s central coast. The populations in Alaska (northern sea otters, Enhydra lutris kenyoni) and in California and Oregon (southern sea otters, Enhydra lutris nereis) are considered geographically separate subspecies.
POPULATION: Historically, as many as 20,000 southern sea otters may have lived along the California coast and Baja California. Wild populations have struggled to recover after being decimated by the fur trade. In January 1977, the southern sea otter was listed as “threatened” under the federal Endangered Species Act. The 2012 census recorded 2,865 total southern sea otters, bringing the three-year running average to just below 2,800 animals. Long-term trends suggest the population recovery has reached a plateau.
THE SURVIVORS: Today’s California sea otters are descended from a small colony found along the isolated Big Sur coast that survived fur hunters. Biologists discovered them in the early 1900s near Point Sur; their existence became widely known in 1938, after the opening of U.S. Highway 1.
HABITAT: Sea otters are found in coastal waters including rocky shores, wetlands and sandy sea bottoms; in ocean depths less than 130 feet where there’s an abundance of food and kelp canopy.
A RECENT SPECIES: Sea otters evolved as a species only 5 to 7 million years ago. They are one of the smallest marine mammals but one of the largest members of the Mustelidae family, a group that includes freshwater otters, weasels and badgers. Adult male southern sea otters weigh approximately 65 pounds; females weigh about 45 pounds. They can grow to be 4 ½ feet long.
THICK FUR: Sea otters have the world’s densest fur – up to a million hairs per square inch in some places. By comparison, humans have about 100,000 hairs in total on the head. Unlike other marine mammals, sea otters lack an insulating layer of blubber, and are dependent on their thick fur to maintain a body temperature of approximately 100°F in ocean waters that can be 35°F to 60°F.
UNIQUE PHYSIQUE: Sea otters’ long whiskers help them detect vibrations in murky waters; sensitive forepaws with retractable claws aid in grooming, locating and capturing prey underwater and in using tools; webbed hind feet act more like flippers, helping propel sea otters through the water; the long, flat tail is used as a rudder and offers additional propulsion; they have blunt teeth designed for cracking and crushing shellfish; and the ability to close their nostrils and small ears prevents water from entering these openings during dives.
HEFTY EATERS: A high metabolic rate lets sea otters convert food into warmth. It also means otters must eat a lot to maintain their body temperature in cold ocean waters – up to one-quarter of their body weight a day in the wild (11 to 16 pounds) just to stay alive.
DEEP DIVERS: When diving for food, sea otters have been known to go as deep as 330 feet, and to remain underwater for up to five minutes. A typical feeding dive lasts just a minute or two, in waters less than 60 feet deep.
VARIED DIET: California sea otters eat a variety of marine invertebrates including shellfish, sea urchins, sea stars, squid and snails. Aquarium researchers have learned that many individual otters specialize in only two to four of the more than 30 food animals available to them – and that food preferences may be passed on from mother to pup.
KEYSTONE SPECIES: Sea otter are considered a keystone species because they are critical to the health and stability of the nearshore marine ecosystem. The species is an apex predator of this ecosystem, living
TOOL USERS: Sea otters use rocks to crack open hard-shelled prey on the surface, either setting a rock on their stomachs while floating on their backs or holding rocks between their forepaws to pound their prey. Abalone- and urchin-eating otters also use rocks to dislodge these tenacious animals from their underwater footholds.
THE FUTURE: The recovery of sea otters in California remains uncertain. Because of their small population and limited geographic distribution, sea otters remain vulnerable to infectious diseases and environmental pollutants, along with the impacts from a major oil spill. Recently there have been increased white shark mortalitie,s too. Scientists and wildlife managers are troubled by the lack of increase in the wild sea otter population, despite decades of protection.