California Sea Otter Mystery

Wildlife pathologist Melissa Miller and her team, clad in rubber gloves, hospital scrubs and big rubber boots, hovered over the animal, looking for gunshot wounds, shark bites, research tags, any visible marks.

The scientists hoped their examination of the male California sea otter would reveal what's killing the threatened sea mammals.

The 4-foot-long, 65-pound adult male was found washed up on the rocks three days earlier at Pismo Beach, south of San Luis Obispo, and driven to a laboratory here for a necropsy.

X-rays showed no trauma, just two toes likely broken a while ago in a fight.

Miller took samples from various organs, tissues and fluids, carefully labeling them for future reference. Like others whose carcasses were found quickly, this one's hide was to be prepared for museums or schools to use in teaching.

Researchers hope that by also looking at the otters' environment they could help the animals recover and keep a key stretch of the ocean healthy.

California sea otters, with their luxuriously soft pelts, were hunted to near extinction by the early 20th century, but have since recovered somewhat, reaching a recent population high of 2,377 off the California coast in 1995.

Since then, however, their numbers have at best stagnated, and at worst decreased, along much of their range, which once extended all along the West Coast, and now is limited to California's central coast. A survey last fall put their numbers at 2,202.

The mammals live up to two miles offshore, mostly in the forests of kelp that are home to many species.

Despite concerted efforts to figure out what's killing them, it's not entirely clear. Sharks and orcas are among their few predators. Fishing nets have killed otters in the past, and may still, to some extent. Occasionally, one gets shot.

Many of those dying are adults in their prime reproductive years, from about 3 to 9 years old.

The U.S. Fish and Wildlife Service, among other agencies, has been studying the problem intensely. After 16 years of delays and false starts, the federal agency this month released a new otter recovery plan, which blames human activities for the decline in the California sea otter population.

It recommends reducing oil spills, ocean pollutants and entanglements with boat motors and fishing gear. It calls for more research to determine why otters haven't recovered after being named a threatened species in 1977, and it sets a higher threshold for when the population can be considered recovered enough to lose protection under the federal Endangered Species Act: 3,090 animals, up from 2,650 set decades ago.

The plan says the otter population would have to reach 8,400 animals before the species would be no longer listed as "depleted" under the Marine Mammal Protection Act.

"They are an important sentinel of what's happening in near-shore marine health," Miller said. "It could have broader implications for other marine mammals and for us. We eat the same foods; we swim in the same waters."

And without otters, the marine ecosystem can change significantly. For example, sea urchins are a favorite otter food, but when otters are gone, the urchins are unchecked and decimate kelp forests.

Scientists do what they can to understand the playful animals while they're still alive. They tag some, count them each spring and fall, and study their eating and resting habits. They also study their carcasses.

Every dead otter found gets some kind of exam, frequently here at the state Department of Fish and Game's Marine Wildlife Veterinary Care and Research Center, to try to determine the cause of death.

The same parts of every examined otter are taken to build a standard bank of otter parts collected over many years. That gives scientists something to compare and refer to if they discover a new otter affliction. They also take photos for teaching purposes.

For the most part, this otter appeared healthy.

"If he had a chronic disease, he hid it well," Miller said.

She did, however, find that he had very wet lungs, which led her to conclude he drowned. For the sea-going mammals, drowning is frequent, but it's often triggered by something else, such as being hit by a boat.

Infectious disease seems to be one of the biggest culprits in otter deaths. Disease has always claimed otter lives, but recent research by Miller has shown that a protozoan parasite, Toxoplasma gondii, typically found on land, is more common in water than previously recognized and is finding its way into sea otters.

The parasite causes encephalitis that is killing some otters. More than 60 percent of the dead otters examined are found to have antibodies to this parasite.

Research by veterinarian Christine Kreuder, who like Miller is affiliated with the University of California, Davis, shows that a high number are dying of heart disease, odd for a wildlife population. The heart disease is thought to be caused by a virus that inflames heart tissue, causing scarring that leads to heart failure. It can also happen when the immune system starts attacking itself, which could be triggered by bacteria.

But scientists also think the dead otters they retrieve - mostly those that have washed up on shore - are not representative of the entire otter population.

"All we really know is what we see washed up on the beach, and we're suspicious that's biased," said Jim Estes, a researcher with the U.S. Geological Survey. "There's a concern that animals dying from certain reasons are less likely to be deposited on land."

An example: Otters that drown in fishing nets and are discarded may sink and be eaten by predators. Also, otters that wash up from roughly Carmel south to Estero Bay can't be recovered because the shoreline is too rocky, leaving a 100-mile-long gap in the research area.

For now, the male on the stainless steel table joins the many otters whose deaths are a mystery.

By Colleen Valles