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California Sea-Otter Numbers Climb for Second Consecutive Year

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Kayakers and a sea otter.
Above: Kayakers and a sea otter (foreground) share the waters of Elkhorn Slough, CA. Photograph by Paula Messina, San Jose State University. [larger version]
Observers tallied a record-high total of 2,825 California sea otters for the 2004 spring survey led by the U.S. Geological Survey (USGS). The 2004 total marked the second consecutive year the threatened population has shown an appreciable increase in numbers, up 12.8 percent over the 2003 total of 2,505 otters.

"The latest 3-year running average of the three most recent spring counts is up 9.8 percent, to 2,490 sea otters," said survey organizer Brian Hatfield, a USGS biologist in California. The use of 3-year running averages in assessing trends is the approach recommended by the Southern Sea Otter Recovery Team to reduce the influence of any anomalous counts in a given year. For the southern sea otter to no longer be considered "threatened" under the Endangered Species Act, a 3-year running average count of at least 3,090 sea otters would need to be sustained for 3 consecutive years.

The recent increase in sea otters, however, apparently has not occurred across all segments of the population evenly. "Most of the recent increase has been in areas dominated by male sea otters," said USGS scientist Jim Estes. "Numbers of reproductive females have remained roughly stable for the past decade, or perhaps even longer."

Graph  shows number of sea otters counted in California spring surveys since 1983.
graph shows 3-year running averages of the same data
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: Values for 2002 are averages of the 2001, 2002, and 2003 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.

Though encouraged by the high count, the scientists have not yet fully assessed what it means for the recovery of the southern sea otter. Elevated sea-otter mortality has hindered recovery of the population. "We are assembling a recovery-implementation team to address this and other recovery issues," said Greg Sanders, southern sea-otter-recovery coordinator for the U.S. Fish and Wildlife Service. "Increasing sea-otter numbers will help us reach our recovery goals, but ultimately we must address the underlying threats to the population."

Scientists from Federal and State agencies, universities, and the Monterey Bay Aquarium have been working collaboratively to better understand why the California sea otter has not yet fully recovered. The team is using radio transmitters and time-depth recorders in dozens of tagged sea otters to track and monitor behavior and vital signs as the animals dive and forage for food. Preliminary results from these telemetry studies are showing an increase in male survival in recent years, but not in female survival.

"By very precisely and closely following these tagged individuals, we are taking a qualitatively new look into the population," said Estes. "From these individuals we will be able to make a sounder assessment as to what causes them to die or acts on their mortality, and the relative proportion of various threats." Additional insight into mortality comes from detailed necropsies by the California Department of Fish and Game of freshly dead sea otters found stranded along the California coast.

The spring 2004 California sea-otter survey was conducted May 6-21, from Point San Pedro in the north to Rincon Point in the south, in overall viewing conditions slightly less favorable than for spring 2003. The spring survey is a cooperative effort of the USGS, the California Department of Fish and Game's Marine Wildlife Care and Research Center, the Monterey Bay Aquarium, and many experienced and dedicated volunteers. The information gathered from spring surveys is used by Federal and State wildlife agencies in making decisions about the management of this small sea mammal.

On June 15, a new high-definition USGS video product was premiered on HDNet. The program, "Precipice of Survival: The Southern Sea Otter," explains how the sea otter population in central California, slowly recovering from near-extinction after the 18th- and 19th-century fur trade, is being studied by a diverse team of scientists and volunteers whose collaborative research effort may provide key information for the sea otters' recovery. The program will air repeatedly on HDNet over the next year.

Related Sound Waves Stories
Collapsing Populations of Marine Mammals—the North Pacific's Whaling Legacy?
October 2003
California Sea Otter Numbers Are Up for the 2003 Census
July 2003
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
Woods Hole Field Center
U.S. Geological Survey (USGS), Woods Hole, MA
Sea Otter Research at WERC
U.S. Geological Survey (USGS)
Sea Otter Research
State of California
high-definition television network

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Marianas Submarine Hydrothermal Systems

Phosphorus Plume Study

Sea-Otter Numbers at Record High

Research West-Central Florida Project Concludes

Outreach South Florida Congressional Staff Tour

Florida Oceans Day

USF Hydrogeology Field Camp

ASLO Keynote Address

Oceanography Camp for Girls

Water Conservation Festival

Meetings Basics of the Basin Research Symposium

Swarm Modeling Workshop

Awards USGS Recognized for ArcIMS Data

Staff & Center News Halley Interviewed for Local Television

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