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Sea Otter Recovery Agencies Concerned About Dramatic Rise in Otter Deaths

Date Posted: May 6, 2003

4/29/2003 Service News Release: April mortalities more than double the 10-year average for threatened population

Forty-four southern sea otters have washed up dead on California beaches this month, a dramatic and as-yet unexplained increase in mortalities among the threatened marine mammal population.

The U.S. Fish and Wildlife Service, which earlier this month released its comprehensive sea otter recovery plan, may soon declare that the deaths constitute an "unusual mortality event." The declaration would free additional resources to search for an underlying cause for the deaths.

"I'm not ready to push a panic button," said Greg Sanders, Sea Otter Recovery Coordinator with the Fish and Wildlife Service in Ventura. "But anytime you see a large number of southern sea otters dying, it is a concern."

About 91 animals have washed ashore since January 1, and 44 dead animals have been reported in April alone. Mortalities this April are more than double the 10-year average of 20 stranding deaths, Sanders said.

The dead include adults in the prime breeding population as well as pups and older animals, said Dave Jessup, a senior wildlife veterinarian with the California Department of Fish and Game, which takes the lead in conducting necropsies on stranded otters.

"The numbers are high enough that it's a major concern for the population," Jessup said. "Four more (otters) came in this weekend, and it's not stopping."

The Monterey Bay Aquarium, which cares for otters that strand alive on beaches and rocky-shore areas, has also logged a record number of sea otters in 2003, said Andrew Johnson, the aquarium's sea otter program manager. This year, 17 animals have come into the stranding program, compared with the previous high: 12 otters during the first four months of the year in 1998.

In 2002, only four live-stranded animals came to the aquarium during the same period, he said.

"If the population were growing, you'd expect to see more strandings and more dead animals," Johnson said. "What makes this worrisome is that strandings have increased at a time when the population is essentially static."

Thus far, Jessup said, no patterns are emerging that offers an easy explanation for the deaths.

"Prime-age animals are dying of a variety of infectious diseases and parasites," he said, and three animals died of injuries that occurred when they were struck by boats.

The recovery plan identifies high mortality among prime-age sea otters as a significant threat to the long-term recovery of the species. Oil spills remain a major danger, but scientists are increasingly concerned about the rise in infectious disease and problems with parasites, developments that may point to pollution of the otters' coastal habitat as a key factor in what Sanders called their "lackluster" recovery.

The increased mortalities this year have occurred throughout the otters' range, from the San Francisco Bay area to Santa Barbara, Sanders said. The highest concentration of deaths is around Monterey Bay, he said.

The last time sea otter deaths rose this dramatically was in 1998, during an El NiƱo event, Sanders said. He has contacted a working group of sea otter experts for their concurrence that this year's deaths constitute an "unusual mortality event." If they agree, Sanders said, an on-scene coordinator could be designated to investigate the mortalities, or additional resources put into necropsies that might pinpoint a cause.

"Unless we get additional support for tissue analysis of dead animals, we may miss something subtle that underlies this increase in deaths," Jessup noted.

The spring 2002 sea otter census counted 2,139 sea otters in California. The highest count, in 1995, tallied 2,377 animals. The 2003 census begins in May.

Monterey Bay Aquarium:
Mimi Hahn (831) 648-4918 and Ken Peterson (831) 648-4922

U.S. Fish & Wildlife Service:
Greg Sanders, (805) 644-1766

California Department of Fish And Game:
Dave Jessup, (831) 469-1726

U.S. Fish and Wildlife Service, Division of Environmental Quality. News Release: Evaluating Contaminant Impacts to Sea Otters Along Washington's Coast.

U.S. Fish and Wildlife Service. News Release - Sea Otter Recovery Agencies Concerned About Dramatic Rise in Sea Otter Deaths

U.S. Fish and Wildlife Service, Ventura Field Office

California Department of Fish and Game

Monterey Bay Aquarium

Last updated: June 12, 2015