California Coast & Ocean

In 1977, southern sea otters were listed as threatened under the Endangered Species Act. At that time, a population of 2,650 was considered the threshold for removing them from the list. In 2003, however, the U.S. Fish and Wildlife Service released a revised otter recovery plan; the threshold was bumped up to 3,090, and a count of 8,400 was deemed necessary for the otter population to no longer be listed as "depleted" under the Marine Mammal Protection Act of 1972.

A particularly alarming trend is that a large number of adult females are dying. Dave Jessup, a veterinarian with the California Department of Fish and Game (DFG), observed, "The death of breeding females isn't new, but it seems to be increasing over the last five to 10 years--and that, of course, is the worst thing that can happen."

Overall demographics are worrisome as well. According to Andy Johnson of the Monterey Bay Aquarium (MBA) Sea Otter Research and Conservation program, in 2006 about 280 dead animals were salvaged statewide, a little more than 10 percent of the population. "Based on modeling," he said, "we figure that we're getting close to 50 percent of the animals that die every year. Some animals die at sea and don't come to shore, and we get very few of the animals in the Big Sur area." That means, he said, that "a full 20 percent of the population is expiring every year. And we're barely counting that many pups."

Knowledge gained from the carcass-salvage program is critical to the sea otter's chances for recovery. Those found on the beach are sent for analysis to the USGS National Wildlife Health Center in Santa Cruz, the DFG Marine Wildlife Veterinary Care and Research Center in Moss Landing, or the University of California at Davis (UCD), where necropsies are performed--more or less detailed, depending on how fresh the carcass is. More than 40 percent of deaths have been attributed to various infectious diseases, a rate that has remained relatively consistent for prime-aged adults since studies began in 1992. Jim Estes, a research scientist with the USGS, points out that although a high percentage of Alaskan sea otters also die of disease, "the thing that is distinguishing between the two is that there tends to be a much wider range of diseases here in California."

Pesticides and persistent organic pollutants pose additional threats to otters in coastal California, especially in places like Monterey Bay and Morro Bay, which are relatively dirty environments. Pollutants from such sources as agricultural runoff, sewage plants, and boatyards, as well as DDT and PCBs that accumulated in coastal waters years ago, no doubt have deleterious effects. Although they are not occurring in levels that are acutely toxic, said Jessup, "we have to believe that they are not good for sea otters, probably not good for harbor seals, probably not good for people that eat or collect shellfish either recreationally or commercially. We can't say they are killing 'this many' sea otters, but they may be messing with their immune system, with their reproductive system, with various endocrine systems in the animal that make them more susceptible."

Sharks, boat strikes, and humans with guns remain big threats, of course. And there's also the sea otter's own inquisitiveness, which, when it leads an animal to investigate a lobster pot or Dungeness crab trap and become trapped itself, has dire consequences. Curiosity kills sea otters, but unlike the host of T. gondii, otters don't have nine lives.

Pinpointing the Problem
Researchers have learned a lot about sea otter mortality over the past few decades from sea otter counts and beach-cast carcasses. They've also turned to live, free-ranging otters for information--a more costly and time-consuming, but equally essential, job.

Presently USGS and CDG researchers are tracking almost 100 animals in order to study lifestyle and well-being. When these animals are captured, both initially and at subsequent times through their lives, blood samples are taken and detailed health profiles logged. In this way, researchers can follow exposure to infectious disease, exposure to contaminants (body burdens), and immune functions. By implanting radio transmitters and time-depth recorders, they can study such things as foraging strategies, prey selection, and range of travel. "And when they die," said Jim Estes of the USGS, "we are watching them, so we can pick them up very quickly and see what they died from." Eventually, Estes hopes that the instruments implanted in the animals will be recoverable even from those that drown in fishing pots, providing information about mortality that is currently unavailable. Researchers are also using these data to compare California otters with otter populations elsewhere that are doing better and see if there are significant differences.

Investigations don't stop with the otters themselves, however. At UC Davis, parasitologist Pat Conrad, a key player in identifying Toxoplasma gondii's role in sea otter mortality, is leading an integrated study that will bring together terrestrial and marine ecologists, oceanographers, and epidemiologists to look at, in addition to otter ecology, the ecology of the parasite and its hosts (especially cats of all stripes) and land-runoff ecology. It's all about the land-sea interface, full understanding of which will be vital not only for sea otters, but for the overall health of our nearshore marine environment. As Andy Johnson of the Monterey Bay Aquarium said, "We're really just at the cusp of linking disease with either particular natural history activities, things that are occurring within the natural system, or things that are being introduced from the land, either by people or animals."

AB 2485, which mandates labeling of cat litter, will also assist this effort by creating a research program administered through the Coastal Conservancy to study, in part, sea otter mortality from non-point source pollution, such as freshwater runoff. Although many indicators point to runoff as the major source of land-based disease in otters, both Estes and Jessup suggest that more specific sources, or hot spots, will begin to be identifiable in the otters' range. "Both for urea [which stimulates the production of domoic acid] and for some of the persistent organic pollutants," said Jessup, "we have accumulating evidence in sea otters, in mussels, and in the grab samples taken by the state and regional water quality boards" that what were thought to be non-point source pollutants in fact have localized origins.

With a little more funding, Johnson said, researchers will begin getting refined answers to questions about why the otter population is struggling so. The more they learn, the more prepared scientists and conservationists will be to call for changes. "It's probably going to be some sort of restriction or legislation or other provision to limit or fix what we're dumping into the nearshore environment," he suggested. "And those fixes are probably going to be expensive. So you have to have real pinpoint information or nobody's going to buy it."

All of us can play a role in helping this research along. Indeed, we should. As Dave Jessup put it: "All of the causes of otter mortality have human health concerns. There are reasons to be concerned about their effects on other marine species. . . . Sea otter health, human health, and marine ecosystem health and diversity are together on these things. It's not simply that we need to do this [work] for sea otters. We need to do it because it's the right thing on a whole lot of fronts."

This article is abridged. For the complete story see the print edition of Coast & Ocean.