Sea otters evoke strong emotions in humans. Most of us can’t help but say, “Ahhhh!” when we see a cute furry otter floating on its back or looking at us in surprise, front flippers held high in the air. Watching a baby sea otter sitting on its mother’s stomach, or hearing one break open a clam on a rock makes most of us smile. Many fishermen, though, are not fond of sea otters and for a good reason. Sea otters are so efficient at finding and eating shellfish that they are able to reduce populations of abalones, clams, and sea urchins to the point where a commercial fishery for these species is not viable in areas with large sea otter populations. In this post and my next two posts, I’ll discuss sea otters and their fascinating biology and behavior.
While sea otters are the second smallest marine mammal, they are the largest members of the mustelid family, which also includes freshwater otters, weasels, minks, skunks and badgers. Sea otters may weigh as much as 100 lbs (45.5 kg). The average adult California female weighs 44 lbs. (20 kg), and the average male weighs 64 lbs. (29 kg). In Alaska, the average adult female is 4 ft. (1.2 meters) long and weighs 60 lbs. (27.3 kg), while the average adult male is 5 ft. (1.5 meters) long and weighs 70 lbs. (31.8 kg).
Sea otters are the only mustelid in the genus Enhydra, and they are significantly different from all other mustelids. Sea otters are one of nine to thirteen (taxonomists disagree on the exact number) species of otters found around the world. Except for sea otters and the endangered species of marine otters, all other otters live primarily in freshwater, although river otters (Lutra canadensis) travel freely between rivers and the ocean, and on Kodiak, it is common to see river otters swimming near shore in the ocean. River otters and sea otters resemble each other, but sea otters are larger and weigh two to three times more than river otters. Sea otters have adapted to a life in the ocean with hind feet that are webbed to the tips of their toes and resemble flippers. River otters also have webbed feet, but they are small, making it easier for river otters to move on land, while sea otters are very clumsy out of water. A sea otter’s tail is flat and looks like a paddle, while a river otter has a long, round tail that tapers to a point. The claws in the forepaws of a sea otter can be extended, but those of a river otter cannot. River otters swim on their stomachs, and although sea otters can also swim on their stomachs, they usually swim on their backs while paddling with their hind flippers. River otters give birth to litters of up to four pups, but sea otters, like other marine mammals, usually only give birth to a single pup.
There are three subspecies of sea otters. Enhydra lutris lutris ranges from the Kuril Islands to the Commander Islands in the western Pacific Ocean. The sea otters in this subspecies are the largest and have a wide skull and short nasal bones. The Southern sea otters, or the California sea otters as they are commonly called (Enhydra lutris nereis), are found off the coast of central California. Sea otters in this group are smaller and have a narrower skull with a long rostrum and small teeth. The vast majority of sea otters belong to the subspecies Enhydra lutris kenyoni, the Northern sea otters. This subspecies ranges from the Aleutian Islands to British Columbia, Washington, and northern Oregon.
Before the 1700’s, an estimated 150,000 to 300,000 sea otters inhabited the area from northern Japan to the Alaska Peninsula and along the Pacific coast of North America to southern California. Between 1741 and 1911 when sea otters were aggressively harvested for their luxurious furs, the population dropped to only 1000 to 2000 animals, and they had been eliminated from much of their original range. Many biologists believed the population was headed toward extinction. In 1911, the International Fur Seal Treaty was signed by the U.S., Russia, Great Britain, and Japan, stopping the commercial hunting of sea otters, and slowly, their numbers began to increase. Sea otters began re-colonizing much of their former range and were reintroduced to other areas. Sea otters now occupy about two-thirds of their historical range.
Counts between 2004 and 2007 estimate the worldwide sea otter population at approximately 107,000 animals. Sea otter populations are considered stable in most areas, although California populations have plateaued or slightly decreased, and there has been a drastic decline in sea otter numbers in southwest Alaska, from Kodiak Island through the western Aleutian Islands. This area once contained more than half of the world’s sea otters, but the population has declined by at least 55 to 67 percent since the mid 1980’s, and in 2005, the U.S. Fish and Wildlife Service listed this distinct population segment as Threatened under the Endangered Species Act. In 1973, the otter population in Alaska was estimated at between 100,000 and 125,000 animals, but by 2006, the population had fallen to approximately 73,000 animals, mainly due to declines in the Southwest Alaska District Population Segment. The cause of this decline is unclear, but evidence suggests that it may be due to increased predation by killer whales.
Be sure to sign up for my Mystery Newsletter on my home page. The second letter will be mailed soon.