2 more reports of alien species

Experts still unsure whether mitten crabs threaten environment

August 12, 2006|By TOM PELTON | TOM PELTON,SUN REPORTER

Two more Chinese mitten crabs have been reported in the Chesapeake Bay, one near Solomons, and another south of Annapolis - raising questions about whether the exotic species has spread over a large part of the estuary, a scientist said yesterday.

The Maryland Department of Natural Resources asked people this month to be on the lookout for the hairy-clawed, spider-legged critters because a pair were found in the Patapsco River near Baltimore.

The crabs are savored as a delicacy in Asia, but they have multiplied so fast when accidentally introduced in Europe and California that they are considered an invasive species, a pest that can clog water-intake pipes and cause other problems.

Gregory Ruiz, a biologist with the Smithsonian Environmental Research Center, said yesterday the most recent sightings are credible but still unconfirmed. He said it's too early to tell whether the sightings mean that the crabs are now breeding in the bay.

"It's a bit hard to say what this means," Ruiz said of the two recent reports. "These are areas that are further away from the Patapsco River, and so if they really are mitten crabs, it suggests they are more broadly distributed."

Michael Slattery, assistant secretary of the Maryland Department of Natural Resources, said: "It's not yet cause for alarm, but it's certainly something we should be concerned about."

After newspapers ran photographs of mitten crabs this week, two watermen called Ruiz and a state biologist to report that they had separately caught similar-looking crabs near Solomons and south of Annapolis in May and June, Ruiz said.

The fishermen didn't keep the crabs, so scientists have not been able to confirm that they were mitten crabs, Ruiz said.

Several other calls about possible sightings came in this week, but they were deemed less credible because the callers saw smaller crabs that could have been confused with local species, Ruiz said.

Adult mitten crabs are about the size of a dinner plate, with white claws surrounded by tufts of black hair.

"We are planning to ramp up our search efforts," Ruiz said.

A team of biologists is considering setting traps and nets and searching river banks for crab burrows this fall, when they normally migrate in large numbers, Ruiz said.

A California biologist said yesterday that an invasion of the Chinese crabs in San Francisco Bay during the 1990s didn't cause much obvious environmental harm.

Tanya Veldhuizen, a scientist with the California Department of Water Resources, said the exotic crabs were first discovered in San Francisco Bay in 1992.

She said the crabs might have been accidentally carried to California in a ship's ballast water, a theory also being considered in Maryland. Or the crabs might have been illegally smuggled into the country as part of a thriving black market for mitten crab eggs, which are considered an aphrodisiac.

"There is a huge market for live mitten crabs in the U.S.," Veldhuizen said. "It's illegal, but people really want the ripe ovaries. They call it `crab butter,' and it's considered a delicacy."

The mitten crabs boomed in the San Francisco area around 1998, with tiny offspring scuttling up rivers in thick sheets and clogging some water-intake pipes, Veldhuizen said.

But since then, there's been a near total dropoff in population, perhaps caused by cold winters, she said.

"The worst-case scenario of what would happen never happened," Veldhuizen said. "We feared that they would do extensive burrowing and that would cause extensive damage to earthen dams and levies. We didn't see that."

Because other invasive species have caused trouble, the Coast Guard plans to introduce regulations requiring ships to kill organisms swimming in their ballast water, said Richard Everett, environmental protection specialist with the Coast Guard. The regulations could require ships to add chemicals to treat the water, or use ultraviolet radiation to destroy crabs, larvae and other stowaways, he said.

Since 2004, ships have been required to dump their ballast water more than 250 miles from shore, so they won't carry invaders into ports. But many ships don't follow this procedure because they aren't designed to do it safely at sea, and it isn't required in heavy weather. So ballast water carrying exotic organisms is often released near ports, Everett said.

"If we can get all the vessels to treat all of their ballast water, we would be in a much more protective situation," Everett said.

tom.pelton@baltsun.com

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