Department of Water Resources
A daily compilation of significant news articles and comment
June 11, 2007
3. Watersheds -
Latest sea otter census prompts concerns
Experts fear the effects of water pollution and attacks from within the population are limiting the species'
San Francisco Chronicle – 6/11/07
From the Associated Press
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
"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
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
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
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.
Equipped with binoculars and portable telescopes, they spent three days scanning near-shore waters, adding up the number of animals they saw, and noting whether they were foraging for food, swimming to a new spot or resting.
The task is tricky because sea otter heads can look like floating kelp from a distance. Bentall and Tinker also could be missing otters hidden by rocks or scared off by scuba divers and kayakers who were sharing the water on an unseasonably clear day.
To help find animals among the rolling waves, the two scientists sometimes follow seagulls that hope 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," Tinker said. "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 had expected. After observing the injured mother, Tinker said the marauding suitor might 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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