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California Sea Otter Numbers Are Up for the 2003 Census

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Sea otter
Sea otter in Elkhorn Slough. Photograph by Paula Messina, San Jose State University.

Counters tallied a total of 2,505 California sea otters in 2003, 17 percent more than the total of 2,139 sea otters in 2002, according to a survey led by the U.S. Geological Survey (USGS). Excellent to good counting conditions sped the 2003 census to a near-record time, running May 10-15.

"This is the highest total count and the highest count of adult and young adult sea otters, 2,270, since current standardized methods came into practice in 1983," said survey organizer Brian Hatfield, a USGS biologist in California. The total number of dependent pups counted was 235.

The survey is conducted cooperatively with the California Department of Fish and Game, the Monterey Bay Aquarium, the U.S. Fish and Wildlife Service, and other agencies and organizations. The information gathered from spring surveys is used by Federal and State wildlife agencies in making decisions about the management of this sea mammal.

This year's survey also marks the greatest differential on record in totals for spring counts between any two sequential years. While the increased number of sea otters in the spring 2003 count is a hopeful sign that the California population may be increasing, the number is not necessarily indicative of an overall population increase, said Jim Estes, a USGS scientist. Spring counts have varied quite widely since 1999.

The U.S. Fish and Wildlife Service's Southern Sea Otter Recovery Plan recommends that trend analyses be based on 3-year running averages to reduce the influence of anomalously high or low counts during any particular year. Factors that can influence the count include viewing conditions, abundance and species composition of surface-canopy kelp, observer experience, and distribution and movements of the animals.

"The 3-year running averages do indicate a gradual but statistically significant population increase of about 0.9 percent per year since 1998; however, this result is strongly driven by the high 2003 count," said Estes. "As is always the case, the meaning of this data point will not become clear for several more years."

number of sea otters counted in California spring surveys since 1983
3-year running averages of number of sea otters counted in California spring surveys since 1983
Otter population: Graph on top shows number of sea otters counted in California spring surveys since 1983; graph on bottom shows 3-year running averages of the same data. (Example: Value for 2001 is the average of the 2000, 2001, and 2002 counts.) Scientists use 3-year running averages—which reduce the influence of anomalously high or low counts during any particular year—to assess whether the California sea-otter population is growing or declining.

Hatfield said most of the increase in numbers of sea otters counted between 2002 and 2003 occurred in Monterey Bay, where observers counted 169 sea otters in 2002 and 503 in 2003. Elsewhere, the numbers for 2003 were mostly similar to those obtained in 2002. Excellent viewing conditions encountered by the aerial team likely contributed to the increase in the number of sea otters counted in Monterey Bay.

In central California, a short-term change in sea-otter habitat and food availability may also have contributed to higher numbers in Monterey Bay, noted Estes. Early storms and large waves during winter 2002-2003 greatly reduced kelp canopies—which sea otters use for resting and foraging—in several exposed outer-coast areas within the sea otter's range in central California.

Along some stretches of coast, the number of sea otters counted was reduced from previous years, and some "missing" sea otters may have moved into Monterey Bay. Elevated numbers of Dungeness crabs may also have contributed to the unusually large number of sea otters in Monterey Bay.

"We're cautiously optimistic about the increase in sea-otter numbers for this year, but elevated sea-otter mortality is still hindering recovery," said Greg Sanders, U.S. Fish and Wildlife Service sea-otter coordinator. "In the long run, we have to minimize deaths of these animals."

The greatly elevated number of sea otters in Monterey Bay and, to a lesser extent, in Estero Bay near the town of Morro Bay, about 110 miles south of Monterey Bay, may also help explain the record high number of strandings this year—a preliminary figure of 116 strandings reported from January through May 2003, said Estes. The probability of recovering stranded sea otters is greater in the Monterey Bay and Estero Bay areas than in most other areas of central California; together, these two stretches of coast account for 63 percent of all recovered carcasses in California.

Related Sound Waves Stories
California Sea Otter Numbers Slide for Second Straight Year
July 2002
Congressional Briefing on California Sea Otter Research
March 2002
What's Wrong with the California Sea Otter?
February 2002

Related Web Sites
Sea Otter Research
U.S. Geological Survey (USGS)

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