The Mystery of the Vanishing California Sea Otters

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Southern sea otter

America's westward expansion went hard on the California sea otter, which seemed to vanish in the first half of the 19th century, an unlucky victim of the fur trade. But the iconic mammal was rediscovered on the Big Sur coast in 1939, and has been making a gradual comeback ever since — or had been. Based on the past three annual tallies of the furry, coast-clinging shellfish eaters, the species — whose population hovers just above 2,500 individuals — seems to be slipping, and investigators simply cannot pinpoint why.

"All the research we have done to date suggests that there's no one single mortality factor," says Tim Tinker, who runs the U.S. Geological Survey's (USGS) otter research program from his office in Santa Cruz, "but that the deaths are caused by a suite of interacting stressors."

That list includes both natural causes — such as food shortages, low genetic diversity, parasites that come from cat pee and possum poop, and a recent rise in shark attacks — and human-caused ones, from dirty ocean water caused by urban runoff, farming fertilizers and remnant pesticides like DDT to accidental catches by fishermen and poaching. And since the small population lives along a confined stretch of coast from northern Santa Barbara County to southern San Mateo County, everyone worries that a disastrous oil spill — most likely from the collision of tankers off the Central California coast — could wipe out the whole species. Why the animals don't spread out more is a mystery. "Even if food is limiting the central population," said Tinker, "it doesn't explain why there is not faster growth at the edges of the ranges."

The USGS is not the only group exploring the problem. So too is The Otter Project, a straightforwardly named organization dedicated to studying and protecting otters. What causes the project's executive director Steve Shimek the most worry is that we already know so much about the species — and yet still can't seem to figure out what's putting it in such danger. "The California sea otter is one of the most researched marine mammals on the planet," he says, "so if we don't have enough information to take action on behalf of the sea otter, I would say that 90% of the other endangered species in the world are doomed. We are taking action to save species that we know far, far, far less about."

It's not that the government has done nothing to protect at-risk otters: the southern sea otter (as opposed to the species that thrives in the Pacific Northwest) was listed as "threatened" in 1977 and the U.S. Fish and Wildlife Service has issued a number of recovery plans since then. But those plans — which attempted to establish a separate population at remote San Nicolas Island and sought to bar otters from coming south of Point Conception, a nod to fishermen who complained that the hungry beasts would decimate the Channel Islands' shellfish stocks — roundly failed: Only about 40 otters remain at San Nicolas, and since it's hard to tell an otter where it's supposed to go, they've encroached into southern waters repeatedly over the years — though after a time they tend to return to their original, limited range.

"The whole program has fallen apart but it's in this weird limbo," said Santa Barbara attorney Brian Segee, who is representing The Otter Project in a federal lawsuit that will likely make the feds re-examine its efforts. "It's a perverse situation where a threatened species is naturally expanding its range but as soon as it crosses this imaginary line, it is left without the full protection of the Endangered Species Act." That means otters don't have to be considered during offshore oil projects and aren't protected from incidental take by fishermen. "We're very concerned about the 25-year perception that otters don't belong," said Segee, who believes that perception teamed with the lack of protection is one reason why the otters aren't making more of a southern swim.

But implicating fishermen — primarily those who catch lobsters and live fish in traps that, the fishermen say, otters are known to try to sneak into — is something no one wants to do, at least not without the scientific surveys to back up the charge. "If we think otters are getting caught in some sorts of fishing gear, it wouldn't be fair for the research and conservation community to go after fisheries if we don't have the data to support that," said Jim Curland, who advocates for otters with Defenders of Wildlife. "It's just about being careful and not shooting from the hip."

For now, even the most optimistic conservationists have to admit that the numbers are discouraging. Back in the 1970s, most experts thought the southern sea otter population would expand at a swift clip of nearly 20% per year like those in Alaska. But the long-term rate has been much closer to 2.5% and that has left wildlife biologist Jim Estes — considered the species' top expert, having working with it for 40 years straight — dismayed. "My fear is that we're right on the cusp of an equilibrium," he says. "Central California is just barely a suitable place for sea otters to live and if we make it any worse, then they're going to wink out." If we can't look after a species we've been trying so hard to save, it may portend even worse things for the ones we've been overlooking.