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 sport 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 menacing attacker in a rocky cove near Monterey's famed Cannery Row.
The biologists have seen female otters — many nursing babies and 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 following two years of drops — a solid 12 percent, or 334-otter increase that brought the number of adults and pups combined above 3,000 for the first time. 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, a figure still far below the delisting criteria and a 2.4 percent 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, according to Estes.
Scientists are pretty sure elevated mortality rates among adult and young adult otters are responsible for the disappointing comeback, as opposed to low birth rates. Of particular concern is that survival rates for female otters have gone down since the 1980s while increasing for the more mobile males, Tinker said.
"Reproductive-age females, the recovery for the population is entirely dependent on them," he said.
No one knows for sure why the otters are failing to thrive, although there are plenty of theories.
Tests done on the carcasses of dead 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 who never end up on land, so they can't say whether disease or something else 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," Estes 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 percent — throughout the 1980s.
Based on previous growth rates of 13-15 percent seen 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 it off.
"But the population stopped growing," Tinker said.
For the May census, Tinker, a research biologist based at the University of California, 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.
Armed with binoculars and portable telescopes, they spent three days scanning nearshore waters, adding up the number of animals they saw, and noting whether they were foraging for food, swimming to a new spot or resting.
To help find animals among the rolling waves, the two scientists sometimes follow seagulls hoping to snag scraps from the shellfish otters smartly crack open with rocks during voracious feeding sessions.
Still, given its consistency, the census is the most reliable barometer they now have of the population's status.
"It's a pretty fundamental part of tracking this population," says Tinker. "Whether we are doing a study that looks in great detail at contaminants or some other factor in mortality, this long-term data set often becomes a part of that."
Despite the ideal viewing conditions, Tinker and Bentall did not see as many otters as they'd expected. After observing the mother with the bloody face, Tinker said the marauding suitor may have been trying to get the she-otter to wean or abandon her pup, thus making her available for mating.
"When you just describe them as being cute, furry animals, you do them a disservice," Bentall said. "They are incredible survivors."
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