by Amy West
The quintessential fuzzy-faced marine mammals, sea otters give humanity more than just a photographic souvenir. They’re like canaries in the proverbial coal mine—harbingers of ocean health.
Historically, the sea otter population was estimated at 150,000 to 300,000 worldwide. They ranged from northern Japan and Russia along the Aleutian chain on down to the West Coast of the U.S., all the way to Baja. At a million hairs per square inch, their naturally warm coat—the densest of any mammal’s—was treasured by pelt-lovers. Hunters nearly wiped them out in the 18th and 19th centuries; by the time sea otters received protection in 1911, only 2,000 remained. With otters gone from Oregon and Washington, and just pockets of them remaining up north, many believed they would go extinct.
They were thought to have been extirpated in California, but in 1938, 50 or so were spotted in Big Sur. Because of the fragility of the California population, in the late 1980s federal agencies tried to introduce sea otters to San Nicolas Island in the Channel Islands chain, with the idea of having a reserve population in case of an oil spill on the coast. But the attempt was deemed a failure after most of the relocated individuals swam back to the mainland.
Since then, the California sea otter population has inched up to 2,800 animals from the remnant population of 50 (2012 figures). Though missing from Oregon, otters have repopulated areas around the Pacific Rim as far as Hokkaido, Japan, and in 2007 the global sea otter population was estimated at 107,000 individuals, with the Russian population relatively stable at about 27,000 and the Alaska population large (73,000) but declining, possibly due to predation by orcas. The three subspecies of Enhydra lutris—the common, northern, and southern or California sea otter—are genetically distinct.
Unlike their relatives the weasel and skunk, sea otters don’t posses a scent gland. They’re also the only member of the family to be completely marine-based. They can give birth all year round on land or water and usually pup once a year. Normally they eat a quarter of their body weight daily. They can tuck their food in folds of skin under their forearms.
Their combination of waterproof guard hairs and air-trapping, dense underfur is key to otters’ survival, since they don’t have a layer of blubber like other marine mammals (except the manatee). They therefore clean meticulously, which is why an oil spill spells particularly bad news for them.
Sea otters eat shellfish including clams and abalone, sometimes opening the shells by pounding them against a rock balanced on their bellies as they swim. Though sea urchins aren’t exactly inviting to touch, sea otters scoop them up for breakfast, lunch, and dinner. By keeping these pointy kelp grazers in check, otters maintain the kelp beds, earning them the title of keystone species. Removing sea otters can cause species shifts in the ecosystem; an urchin takeover can wipe out the kelp. The otter’s relationship to kelp also helps humans battle carbon emissions. A recent study showed otters helped to retain large amounts of kelp, which uptake atmospheric CO2. This mutually beneficial relationship provides the otters with other kelp-dwelling food, such as octopus and clams, and a nice heavy kelp frond to keep them from drifting away while they snooze.
Michelle Staedler, field coordinator for research conducted under Monterey Bay Aquarium’s Sea Otter Research and Conservation program, has devoted many years to tracking the Central California population, even spanning the release of one during its infancy to its death nearly 15 years later.
It appears several factors play into the sea otter’s slow recovery, at least in California. “Recently we’ve noticed a lot more sea otter deaths from sharks,” said Staedler. “In Alaska, the killer whales are decimating the otter populations. And in those areas,” she says, “the sea urchins have come and eaten the kelp.”
These marine mammals aren’t without controversy, of course. They butt heads with fishermen over shellfish resources, so it’s not unheard of to find a sea otter dead from a gunshot wound. Federal laws protect this threatened species, and the U.S. Fish and Wildlife Service mandates permitting activities around these mammals.
Additionally, the otters must battle many contaminants and infectious diseases—of which some, like the toxin microcystin, found in blue-green algae, are land-based and adversely affect humans (and, in the case of microcystin, dogs). “When we see these different diseases in otters,” says Staedler, “it makes us think and ask questions about what is happening in our environment.”
Here's a short video of a sea otter using a rock to crack open shellfish.