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Sharks Take a Bite Out of Otter Populations

Sep 23, 2014 02:40 PM EDT
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The number of California sea otters, a species on a painfully slow recovery path after facing near extinction, is currently holding steady, but according to new research, great white sharks are partly to blame for their recovery stall.

Researchers from the US Geological Survey (USGS) counted 2,944 otters and pups along the California coast this year, about the same as the 2,939 that were seen last year. Scientists believe that conservation efforts should have made more of a dent in the number of these furry animals, also known as southern sea otters. But these otters are combating pressures from all sides, including hungry predators and lack of food, which may be limiting their growth.

"We are seeing elevated mortality suggestive of food resource limitation in some parts of the range, and increasing mortality from white shark attacks in others," Tim Tinker, a biologist with the University of California, Santa Cruz, said in a statement.

These playful critters, sought after for their luscious fur coats, were nearly wiped out from as many as 18,000 otters, and were thought to be extinct in California by 1938. Despite all obstacles, they have bounced back somewhat, but not to the extent that conservationists would like. Population counts would have to be at least 3,090 for three consecutive years before the California otter could be removed from the US Endangered Species List.

"The recovery of the California sea otter has stalled," Steve Shimek, executive director of the Otter Project, one of California's sea otter recovery programs, told the San Francisco Chronicle. "This is bad news. ... We must redouble our efforts."

But sharks continue to take a bite out of otter populations, and scientists are becoming concerned. Some 340 dead sea otters were found last year, clearly the victims of shark attacks, mostly between Morro Bay and Point Conception, according to Tinker.

Toxins, boat strikes, gunshot wounds and disease have also played a part in keeping the population down, but lack of food may also be playing a significant role.

The good news is not all otter populations have plateaued. Populations on San Nicolas Island, located off Santa Barbara, have grown to about 70 otters from a dangerously low 12 animals in the 1990s.

Still, for the most part southern sea otters, the smallest marine mammal in US waters, are crucial to the marine ecosystem, and more needs to be done to protect their populations, researchers say. For example, they remove urchins that limit kelp forest coverage and crabs that kill important invertebrates in tidal creeks.

"Sea otters are really important parts of the near shore marine ecosystem," Tinker added. "The population overall is not decreasing, so the glass is half full, but there are some definite areas of concern."

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