Chinese crab poses a hairy problem

Pest could menace the native blue

May 19, 2007|By Tom Pelton | Tom Pelton,sun reporter

A hairy-clawed alien keeps turning up in the Chesapeake Bay.

Watermen checking their pots yesterday morning in Southern Maryland found a Chinese mitten crab -- the third confirmed in the bay during the past three years.

The mitten crab is an exotic Asian species that has hitchhiked in ships to California, Germany and England and then exploded in population.

The crabs are savored at dinner tables in China. But outside their native turf, they're often considered pests, because they swarm over riverbanks, dig burrows that cause erosion and rip up fishing nets.

Gregory M. Ruiz, senior scientist at the Smithsonian Environmental Research Center in Edgewater, said the mitten crabs are either reproducing in the Chesapeake Bay or repeatedly being released in the ballast water of ships.

Either could be worrisome, he said, because if they're breeding here, they could suddenly multiply, competing with native Chesapeake blue crabs. Or, if they keep jumping ship from Asia, they could soon settle in, he said.

"It's a concern, because there is a lot of evidence that this crab could establish itself here," said Ruiz, a marine ecologist. "In other places where it has been established, it goes through years where there are outbreaks, and they are incredibly abundant."

Unlike blue crabs, the mittens spend most of their lives in the fresh water of streams and rivers, burrowing into earthen banks, dams and levies, potentially increasing erosion, he said.

They migrate to salt water to breed. In the bay, it's unclear how a mitten crab boom could affect the population of blue crabs, fish and shellfish.

Competition for food

"The blue crab is a tough beast, and head to head, a blue crab could hold its own against a mitten crab," said Ruiz. But he said the two crab species could compete for the same food sources such as submerged aquatic vegetation and young blue crabs and mussels.

"I don't want to be alarmist about it, but there are a lot of potential dynamics that we don't understand," Ruiz said. "Like a lot of invasive species and non-native species, this is not one that we want. We don't want to take that risk."

The Smithsonian center is working with the Maryland Department of Natural Resources and the U.S. Fish and Wildlife Service in issuing an invader watch for the mitten crabs. They are asking anyone who finds one to e-mail sercmittencrab@si.edu.

The mitten crabs have white claws adorned with fuzzy, black, wig-like tufts of hair. They are light brown in color, with a round carapace about 4 inches across and long spindly legs that span about 10 inches. They have no swimming legs.

The first mitten crab identified in the Chesapeake was caught by a waterman last June at the mouth of the Patapsco River and turned over to researchers.

Then, a few days later, scientists concluded that a second crab, also caught in the Patapsco River more than a year earlier and frozen, was of the Chinese species.

After the state issued an alert asking people to report and turn in suspicious crabs, two more watermen phoned in accounts of catching what looked like mitten crabs south of Annapolis and near Solomons. But they didn't keep them, so researchers couldn't confirm what they were.

"I don't know if these numbers are cause for great alarm, but periodically having them turn up like this is cause for some concern," said Eric Schwaab, deputy state natural resources secretary.

Schwaab said that after the extensive publicity surrounding the invasive species alert issued by the state last summer, he would have expected more to have been reported if the crabs were breeding in the bay.

"I don't think this suggests there is a significant population, let alone a growing population," said Schwaab.

But the three reports over three years suggest that the creatures might be riding in the ballast water of ships, he said.

`It looked different'

Vince Meyer, a 40-year-old waterman and owner of Vince's Crabhouse in Essex, caught the most recently reported mitten crab off Chesapeake Beach yesterday in his boat, the Brittany Lynn.

Meyer said he and two friends set off from the docks in Calvert County at dawn on a cloudy, chilly and windy morning.

They checked about 600 crab pots, pulling in about 15 bushels of blue crabs, not a bad catch for this time of year, he said.

At about 9:30 a.m., the crew was approximately a half-mile off Holland Point, in about 14 feet of water, when they pulled up a pot holding a small blue crab and something odd with long, spidery legs.

"It looked different," Meyer recalled. "The legs had like long hairs on them, and the hair had an almost purple color. It was freaky-looking for the bay."

One of his crew members recalled seeing a news story about the Chinese mitten crabs last summer and said it looked similar. So they called the Smithsonian research center, and scientists met them on the docks in the afternoon and confirmed its identity.

If the mitten crabs take off in the bay, Meyer said, the customers at his crab house might have a hard time swallowing them.

"It's a shell with fur on it -- it's hard to say if people would like that," he said. "There ain't much meat in the claws. ... But if it tastes as good, they'll eat it. They eat lobsters and crawfish. Why wouldn't they eat these?"

tom.pelton@baltsun.com

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