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Latest sea otter census prompts concerns

Experts fear the effects of water pollution and attacks from within the population are limiting the species' California population.

June 11, 2007|From the Associated Press

MONTEREY, CALIF. — Training her binoculars on a dark patch of seaweed swaying in the shallows, Gena Bentall gasped. After searching for sea otters all day, the research biologist had spotted one: a mother with a pup on her belly, a mauled face dripping blood and a male pursuer hot on her tail.

Female sea otters often have scars on their noses, the price of breeding with clumsy, sharp-toothed partners.

But vicious injuries like this one are showing up with unusual frequency off the California coast, one of several signs leading marine scientists to suspect something is amiss in the kelp beds where the state's beloved aquatic mammals make their homes.

"This is one of the things that makes us think the sex ratio is skewed in an unhealthy way," said Tim Tinker, another otter expert who joined Bentall in watching the wounded mother try to outswim her attacker in a rocky cove near Monterey's famed Cannery Row.

The biologists have seen female otters -- many nursing babies and thus incapable of getting pregnant -- with their muzzles ripped off. Even young males have become targets of aggressive mating. The culprits are thought to be itinerant, adolescent otters invading the territories of males who typically jealousy guard their harems.

Every spring and fall for the last quarter-century, teams of scientists have fanned out across 375 miles of California coastline to count Southern sea otters, a threatened species that was hunted to near-extinction a century ago. The census is used to gauge whether the struggling population is rebounding or declining, with at least three years of similar results required to demonstrate a trend.

The survey conducted last month brought welcome news after two years of declines -- an increase of 12%, or 334 otters, that brought the number of adults and pups combined above 3,000 for the first time since the census began. For the California sea otter to be removed from the threatened species list, the count would have to average 3,090 or more over three years.

Scientists greeted the figures with measured optimism, noting that unusually balmy and clear weather in early May provided good conditions for a process that is subject to the vagaries of human error and constrained by the limits of the human eye.

More significantly, they note, the average population for the last three years stands at 2,818, far below the delisting criteria but a 2.4% improvement over the previous three-year benchmark. Combined with similarly sluggish growth rates since the mid-1990s, the data suggest the species is hanging on but not bouncing back.

"The fact is the population is not recovering, and we really don't have a good explanation for why," said Jim Estes, a veteran sea otter expert with the U.S. Geological Survey.

Possibly an outgrowth of inbreeding, the disconcerting sexual behavior Tinker and Bentall observed last month isn't killing California's otters in disproportionate numbers, but may be a byproduct of something that is, Estes said.

Scientists are pretty sure that elevated mortality rates, as opposed to low birthrates, among adult and young adult otters are responsible for the disappointing comeback. Of particular concern is that the survival rate for female otters has dropped since the 1980s while that for males, who are more mobile, has increased, Tinker said.

"Reproductive-age females, the recovery for the population is entirely dependent on them," he said.

No one knows why the otters are failing to thrive, although there are plenty of theories.

Tests done on the carcasses of otters that wash ashore suggest they are succumbing to diseases that may be linked to water pollution damaging their immune systems. But scientists cannot know the cause of death for otters that never end up on land, so they can't say whether disease is the problem. Even so, any otter lost to contamination caused by humans is a cause for concern, given their precarious numbers, Estes said.

"Here we have this otter population that seems to be on the cusp," he said. "With a ratcheting down of the quality of the environment, it doesn't bode very well in my mind for the future, which is just on the balance right now."

The spring count found 1,856 otters when the census was launched in 1982, and the population expanded steadily -- by an average of 6% -- throughout the '80s.

Based on previous growth rates of 13% to 15% in Alaska's Northern sea otters, experts thought it reasonable to expect the California population to climb to about 16,000, the number estimated to have occupied the Pacific Ocean between Oregon and Baja Mexico in the 19th century before hunters seeking the animal's thick, luxurious fur almost killed off the species.

"But the population stopped growing," Tinker said.

For the May census, Tinker, a research biologist based at UC Santa Cruz, and Bentall, who works for the Monterey Bay Aquarium, were assigned to an area that has one of the state's highest concentrations of sea otters.

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