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Discovery of Second Invasive Mitten Crab Raises Worries

Takos was shocked over the weekend to see a photo of a similar crab in the newspaper, after a mitten crab was caught in the same area this June. On Sunday, he called authorities.

"It's a good thing I had the forethought to freeze it," he said yesterday. Despite Takos's suspicions, Ruiz said the crab was male. The crab found in June was also male.

Lipcius said clues to the crabs' appearance could come from shipping operators who may recall ballast accidents or residents who may know of someone who possesses or breeds the creatures.

The mitten crab is fully established in San Francisco Bay, where it was first found in the early 1990s and is believed to have arrived in ship ballast water.

"They are quite problematic. They are very aggressive crabs and compete with our native crabs," said Andrea Swensrud, program manager at the Marine Science Institute in Redwood City, Calif.

The crabs also burrow into levees and banks to make their homes, contributing to erosion and potential flooding problems, she said. In Europe, they weaken dams and clog water intake pipes.

Lipcius believes the chances that the mitten crab has established itself remains small. "There are a lot of hurdles a species like this would have to overcome to become resident," including temperature, migration and adaptation problems, he said, as well as the effect of the bay's infamous pollution.

"We've done many, many surveys throughout the bay, and you'd think we'd have caught them" before, he said. "It's not likely that we have an actual resident viable population, but of course we're on the lookout."

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