Alien crab found in bay prompts `invader' alert

Species has caused damage in San Francisco area

August 05, 2006|By TOM PELTON | TOM PELTON,SUN REPORTER

Waterman John "Hoss" Delp was checking his crab pots near the mouth of the Patapsco River not long ago when he hauled in a trap with a creepy catch.

It looked like a daddy longlegs the size of a dinner plate. Two white claws snapped at him from spindly legs cuffed by fuzzy, black, wig-like tufts of hair.

"I had no idea what I'd caught. I was like, `Man, that's strange. Looks like a big weird spider,'" said Delp, 44, of Pasadena, who has been crabbing the river for three decades.

It turned out he had caught the first Chinese mitten crab in the Chesapeake region. The species is native to Asia and notorious for invading bays in California, Germany, England and elsewhere around the globe, then multiplying like crazy.

Mitten crabs are regarded as a delicacy in China, where the eggs are savored as an aphrodisiac. But they're regarded as a pest outside their homeland because they rip fishing nets, clog water intakes and dig burrows that make Swiss cheese out of earthen dams.

The Maryland Department of Natural Resources sent an alert yesterday to watermen, local government officials and others asking them to be on the lookout for the illegal immigrants.

"I would urge anyone who may come in contact with one to keep the crab, take a photo of it, note the location of the discovery and contact me," said Lynn Fegley, biologist with the state agency. She asked to be contacted at lfegley@dnr.state.md.us.

State biologists are trying to determine whether the male crab was an isolated castaway on a ship that anchored in Baltimore harbor, Fegley said. Or perhaps it's part of a new colony of an invasive species that will overpopulate the Chesapeake Bay as it has San Francisco Bay.

"Any time a species like this shows up, it's impossible to assess what the effects on your ecosystem might be," Fegley said. "There is always the potential that it could throw your ecosystem out of balance."

Exotic marine life is treated with great caution in the Chesapeake Bay and elsewhere. The administration of Gov. Robert L. Ehrlich Jr. stirred an intense scientific debate by suggesting the possible introduction of Asian oysters into the bay to help replace dwindling native bivalve populations. A study on that proposal is scheduled to be finished next year.

State biologists in 2002 poisoned a pond in Crofton in a failed effort to wipe out toothy snakehead fish from Asia - nicknamed "frankenfish" - that are now reproducing in the Potomac River.

The snakeheads have been viewed as a potential menace because they are predators and could devour local fish.

Chinese mitten crabs are illegal to import or sell in America, Fegley said. But they are unlikely to pose a competitive threat to Chesapeake blue crabs because they don't generally eat other crabs - as blue crabs do - and favor different waters, she said.

The Chinese crabs live most of their lives in freshwater streams and rivers, Fegley said. They travel downstream to salt water only to breed once a year. Unlike blue crabs, they don't swim, instead crawling along the bottom.

Blue crabs favor saltier waters and are more mobile. "Will they directly compete with one another? Probably not," Fegley said.

The larger concern is whether mitten crabs would proliferate in local rivers and interfere in unpredictable ways, she said.

Mitten crabs showed up in the San Francisco Bay in 1992. By 1998 they were swarming thick, clogging screens at water purification plants in the region, according to The San Francisco Chronicle.

By contrast, one mitten crab was found in the Columbia River in Oregon in 1998. But it turned out to be an isolated incident, and biologists never found another one.

Gregory Ruiz, a marine ecologist at the Smithsonian Environmental Research Center in Edgewater, said mitten crabs have shown they can survive in climates similar to the Chesapeake region. But he noted that exotic species don't always succeed or pose problems.

More than 150 non-native species are reproducing in the Chesapeake region. Some cause damage; others are accepted as normal.

For example, MSX, a parasite from Asia discovered in the bay in the 1950s, has killed many native oysters and prevented the recovery of the native bivalve.

On the other hand, hydrilla, an invasive aquatic plant, is spreading around the mouth of the Susquehanna River and is considered a valuable habitat for fish.

"Whether it's good or bad is a value judgment," said Ruiz. "When a species moves into a new system, it's difficult to say how it will play out. ... At this point, there is one Chinese mitten crab caught - and we don't know if it's established."

Scientists said yesterday that it's not clear where the crab came from. Mitten crabs are not generally served in local Chinese restaurants, so traveling in a ship's ballast water is a possibility.

Delp said he caught the crab the morning of June 9 at the mouth of the Patapsco River in northern Anne Arundel County, between Rock Creek and Bodkin Creek.

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