MONTEREY, CALIF. ? Training her binoculars on a dark patch of floating seaweed, Gena Bentall gasped. After searching for sea otters all day, the research biologist had spotted one: a mother with a pup on her belly, but the otter’s face was mauled and dripping blood and a male was hot on her tail.

An otter cleans itself in the water in Monterey, Calif., in this May 8 photo. Something is sickening California's sea otters. Research biologists who pace the coastline counting the endangered species see it in the mauled faces of females and the increasingly aggressive mating habits of males that mount other males. While the annual spring census conducted by the U.S. Geological Survey showed a 12 percent rise in the state's sea otter population, scientists say the numbers obscure troubling trends in the kelp beds where the beloved marine mammals make their homes.

Female sea otters often bear scars on their noses, the price of breeding with clumsy, sharp-toothed partners. But vicious injuries like this are showing up with unusual frequency, one of several signs leading marine scientists to suspect something is amiss for the threatened species.

“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 injured 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, which makes them 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 guard their harems jealously.

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

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 scanned the near-shore water for three days, counting otters and noting their activities. The task is tricky since sea otter heads can look an awful lot like floating kelp from a distance. And observers can miss otters hidden by rocks or scared off by scuba divers and kayakers.

Overall, the May survey brought welcome news following two years of declines – 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, clear weather in early May provided good conditions for the census.

More significantly, they note, the average population over the last three years is 2,818, still far below the delisting criteria but 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.