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Fewer California Sea Otters Tallied in Spring 2001 Survey But Population Size Remains Roughly Stable
Released: 6/12/2001

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Gloria Maender 1-click interview
Phone: 520-670-5596

Note to news editors: View a summary of spring surveys of California sea otters for 1983-2001, and three-year averages at http://www.werc.usgs.gov/otters/ca-surveys.html. Information about sea otter mortality can be viewed at http://www.nwhc.usgs.gov/news/seaottrs.html.

Last year up; this year down, but the number of sea otters in California remain roughly stable, neither increasing or decreasing rapidly, according to the scientists who study them. Still, a lack of sustained growth worries researchers and sea otter watchers.

The 2001 spring survey of 2,161 California sea otters reflects an overall decrease of 6.7 percent since the 2000 spring survey of 2,317 individuals, according to scientists at the U.S. Geological Survey. Observers recorded 1,863 adults and subadults, or independents, down 9.25 percent from last year’s count of 2,053 independents. Pups, however, increased by 12.9 percent, to 298 individuals.

Over the last six years, spring counts have ranged from 2,377 individuals recorded in 1995, to 2,090 individuals in 1999. The population appears, however, to have been roughly stable in numbers over the last several years, according to USGS scientists who use trends and running averages to assess whether the population is growing or declining.

"The results of this year’s survey indicate that last year’s high count was an anomaly," said USGS research ecologist Dr. Jim Estes at the USGS Western Ecological Research Center in Santa Cruz, Calif. "No single survey really means very much because these counts are not exact enumerations of the population. Like nearly all wildlife surveys, some animals are missed and this varies from count to count."

Estes continued, "My overall assessment from these data is that the California sea otter population increased from the early 1980’s through the mid 1990’s; declined from the mid 1990’s to late 1990’s; and has been roughly stable over the past several years."

The survey, conducted cooperatively by scientists of the USGS, the California Department of Fish and Game, the Monterey Bay Aquarium, the U.S. Fish and Wildlife Service and experienced volunteers, covered about 375 miles of California coast, from Half Moon Bay south to Santa Barbara. The information gathered will be used by federal and state wildlife agencies in making decisions about the management of this sea mammal.

"The three-year average of survey results indicates that the sea otter population is more or less stable," said Greg Sanders, U.S. Fish and Wildlife Service sea otter coordinator. "However, the numbers fall short of our recovery goal for the species. We would like to see the population increase to reduce the threat of extinction.

Low population growth rate has long been a factor in the lagging recovery of the California sea otter, said Estes. The population of sea otters in central California increased this century at an average annual rate of about five percent until the mid-1970’s, when growth ceased and the population began to decline. Following California’s emergency restrictions on set-net fishing, the population increased again until 1995, but has since declined. In 1977, the California sea otter was listed as threatened under the federal Endangered Species Act.

Entanglement or entrapment in coastal fishing gear, starvation, disease and contaminants may have contributed to the recent sea otter decline, said Estes. The USGS National Wildlife Health Center in Madison, Wis., the California Department of Fish and Game, and the University of California, Davis, have been examining fresh sea otter carcasses to investigate causes of death.

"The survey results underscore the importance of research collaborations to understand what’s happening with the wild population," said Andrew Johnson, Sea Otter Research and Conservation (SORAC) program manager at the Monterey Bay Aquarium. The aquarium’s SORAC program is responsible for rescue and rehabilitation of ill and injured sea otters throughout California. New research is under way at the USGS Western Ecological Research Center to discover causes for the declines in California sea otter populations, by focusing on the behavior and population biology of sea otters. This is a broadly collaborative program involving additional scientists from the California Department of Fish and Game, the University of California at Santa Cruz, the University of California at Davis, the National Wildlife Health Center and the Monterey Bay Aquarium. The scientists are documenting patterns of growth or decline in sea otter populations. They hope to determine the demographic, behavioral, and physiological mechanisms responsible for the different rates of population change, and in particular to understand reasons for depressed growth of the threatened California sea otter. The research also is developing modeling approaches to predict trends, and using radio telemetry and visual observations of marked individuals to compare foraging habits, social behavior, physiological responses and demographic differences among various sea otter populations. Detailed health profiles are being developed for living animals and beach-cast carcasses are being examined and tissues analyzed, in an effort to determine cause of death. Analyses of these data will help indicate the status of a sea otter population and why it is not increasing.

Sea otters historically ranged across the North Pacific Ocean from about the mid-section of the Pacific coast of Baja California, Mexico, to northern Japan. By the end of the 19th century maritime fur traders hunted sea otters to the brink of extinction. About a dozen remnant colonies survived at the time of protection in 1911; one remnant colony occurred along the remote Big Sur Coast of Central California.

The spring 2001 survey was conducted following a USGS survey protocol. Teams used binoculars and spotting scopes to count individuals from shore and from fixed-wing aircraft. The counts made from shore were plotted on maps and then entered into a spatial database. The aerial counts were entered directly into a geographic information system-linked database in the aircraft.

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