(Photo: Don Henderson/Getty Images)

What's Not Trying to Kill California Sea Otters?

Between shark attacks, diseases, algal blooms, and occasional gunfire, the sea otter population on California's coast has stalled.
Sep 26, 2014· 3 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

It's hard to imagine that an animal as wonderful as the California sea otter almost disappeared from the planet.

Once upon a time, tens of thousands of sea otters floated and swam off California's coast. But the fur trade in the 18th and 19th centuries took care of that, nearly wiping out the subspecies, and many people believed that it had gone extinct. But all of that changed in 1938 when the last raft—or group—of around 50 sea otters were found alive and well near the Bixby Canyon Bridge in Big Sur.

That discovery was just the start. Buoyed by conservation efforts from groups such as Friends of the Sea Otter—and later by legal protection under the Endangered Species Act and other laws—the furry marine mammals have made a remarkable recovery over the past 70 years.

Today, there are 2,944 sea otters swimming in California's coastal waters, according to data released this week by the U.S. Geological Survey. Their habitat now ranges from Pigeon Point, north of Monterey Bay, down past Pismo Beach to Gaviota State Beach, just above Santa Barbara. A small population also lives farther out to sea on San Nicolas Island.

Although this year's count represents a new high point since the otters' brush with extinction, the news isn't all good. The 2014 number has only grown by five otters since last year, an indication that the population growth has effectively stopped.

"The recovery of the California sea otter has stalled," Steve Shimek, chief executive of The Otter Project, wrote on the group's Facebook page. "This is bad news. The California sea otter is an iconic endangered species and to see it struggling to scrap back from the brink of extinction is difficult to watch; we must re-double our efforts."

But where should the effort be focused? The latest numbers show the problem isn't otters breeding—it's otters dying.

The 2014 count showed a record number of otter pups in California's population—quite a turnaround from 2010, when the pup count was at one of its lowest points. So why aren't there more otters? Simply put, they're dying off at record numbers, and sharks could be to blame.

(Sharks themselves are in danger from fishing and human predators, who cut off their fins so they can be made into shark fin soup. A mission to hunt down and stop some of these illegal shark finners in Costa Rica appears on the latest episode of The Operatives, a new television series that airs Sundays at 10 p.m. ET/7 p.m. PT on Pivot TV, the television network owned by Participant Media, TakePart’s parent company.)

"We are seeing elevated mortality suggestive of food resource limitation in some parts of the range, and increasing mortality from white shark attacks in others," said Tim Tinker, a USGS biologist who leads the annual sea otter research project.

Shark attacks against sea otters rose 21 percent between 2001 and 2010, and the number of attacks continues to rise. But the sharks don't actually eat the sea otters—the blubber-free animals don't have the levels of fat sharks need in their diet. Instead, they seem to bite the otters thinking they may be other food, and the mammals die as a result of the wounds.

While the pup count is high, researchers noticed an increase in the mortality rate for breeding females this year. The stress of feeding both themselves and their pups appears to be leaving moms underweight and vulnerable to diseases and infections, according to a recent study.

As many as 17 percent of California sea otters die from brain disease caused by the toxoplasma parasite (the same thing you can catch from kitty litter), according to the Sea Otter Alliance, a joint project of several universities and other organizations.

Other perils sea otters face include toxic algal blooms, parasitic worms, bacteria, fungus, and exposure to pollutants and toxins from human activity, as well as oil spills.

As if that weren't enough, still more California sea otters die from a variety of conditions including heart disease, boat strikes, mating trauma (otters have a lot of sharp claws and teeth), cancer and—perhaps most shocking of all—gunshots from humans who continue to kill the animals.

The good news? Amid all of this death, California sea otters really are on the verge of recovery. If they can maintain a population of 3,090 animals for three years, they will become eligible to leave the Endangered Species Act. Only about 100 more adults are needed to reach that level.

Is it possible?

The USGS says researchers are examining how to reduce mortalities from the numerous threats sea otters face, although some factors—such as the growing number of shark attacks—remain a mystery. But the fact that otters are doing well on San Nicolas Island, where a relocation project began a few years ago, indicates that populations can grow beyond the otters' current habitat.

"If sea otters can recolonize new areas of their historic range, we are almost certain to see an upswing in population growth," said Lilian Carswell, southern sea otter recovery coordinator for the U.S. Fish and Wildlife Service. "That will be good for sea otter recovery, good for the nearshore environment, good for all of us—because we all benefit from the services that intact ecosystems provide."