Wildlife researchers are reporting an overall decrease in sea otter numbers in California as well as a significant decrease in the number of pups.
This year’s annual spring survey of the animals showed a 3.6 percent drop in the population over the past three years. Counts are averaged over three years to remove year-to-year variability.
The population is estimated to be 2,711 animals. More alarmingly, the number of pups this year is down 11 percent over last year.
“We have seen a decrease in sea otter numbers throughout most of where most of their reproduction occurs, while pup counts have dropped to 2003 levels,” said Tim Tinker, the lead scientist for the survey with the U.S. Geological Survey.
The drop in pup numbers may be linked to winter storms and the resulting reduction in kelp cover. A record number of pups and juveniles were found washed up on beaches this winter.
Disease and malnutrition are two of the reasons for the overall decline in population, said Brian Hatfield, who coordinates that survey for the USGS out of the Piedras Blancas Lighthouse.
Sea otters mounted a slow but steady recovery over the past decade, but that recovery appears to be faltering. Otters are considered key indicators of ocean health because they are top predators in the near-shore environment where they are subjected to pollution and other human-caused stressors.
To learn more about this, researchers are studying two populations of otters in Monterey County: one in Monterey Bay and the other in Big Sur. The idea is to compare the health of otters in populated and unpopulated areas.
An example of the many diseases found in sea otters is a 16-week-old pup recovered from Morro Strand State Beach that was recently added to the otter exhibit at the Monterey Bay Aquarium.
The pup was prematurely weaned and suffered from peritonitis contracted by eating sand crabs infested with thorny-headed worms.
Researchers also noted these trends in the sea otter population as a result of this year’s survey:
- An unusually high level of mortality in breeding-age females. Many of the females were suffering from what otter biologists call end-lactation syndrome. Females are malnourished because they just finished weaning a pup and then were aggressively mated by males who left bite marks visible on the females’ noses. “It’s a pretty vulnerable time,” Hatfield said. “If they are not getting enough food to build up fat reserves, that adds to the problem.”
- A significant increase in the number of shark-bitten sea otters particularly off San Luis Obispo County. Researchers are not sure whether this increase is due to an increase in sharks or if individual sharks are targeting otters. “We’re pretty sure they don’t eat them,” Hatfield said. “But lots of otters in Estero Bay and off Pismo Beach hang out in open water, which would make them more vulnerable.”
- A slight shrinkage in the overall territory of the otters. Male otters often inhabit the fringes of the territory but moved away from the range edges last year. The animal’s range is Pigeon Point in San Mateo County to Gaviota State Park in Santa Barbara County.
California sea otters are listed as threatened under the federal Endangered Species Act. In order to be removed from the list, otter numbers would have to reach 3,090. If the population drops to 1,850, the animal’s status could be raised to endangered.
Reach David Sneed at 781-7930.