Chinese Crabs Rapidly Invading U.K., Scientists Warn

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The crustacean has been known to migrate more than 900 miles (1,450 kilometers) upriver in China, and it can weaken dikes and riverbanks with its networks of muddy burrows.

Marine biologist Matt Bentley, lead author of the study, compares the crab's threat to that of another invader, the gray squirrel from North America. The squirrel is blamed for pushing Britain's indigenous red squirrel from much of its former range.

"With most invasive species, such as the gray squirrel, the problem is not recognized until it is too late, and you can't eliminate it without taking drastic environmental measures," he said.

Bentley urges action to halt the crab before its numbers spiral out of control.

"Low-cost options could include a public awareness campaign where anglers and other users of rivers and the coastline are encouraged to report sightings," he added.

Writing in the journal Biological Invasions, the Univeristy of Newcastle team also recommends a nationwide trapping program.

In addition, the Natural History Museum in London has launched a one-year study into the possibility of harvesting London's mitten crabs for the city's Chinese restaurants.

"We're looking into the feasibility of fishing or trapping as a potential control method to feed into the restaurant trade," said Philip Rainbow, the museum's keeper of zoology.

Tasty Gonads

In Asia the mitten crab is considered a delicacy. The gonads, which ripen during the crabs' seaward breeding migration, are especially prized.

The Natural History Museum project will assess whether crabs in the Thames are safe to eat and whether they could be caught on a commercial scale for export back to China.

"We know they are suitable for food, but they need to have a clean bill of health from the authorities," Rainbow said.

In Asia the species is known to host parasitic lung flukes, which can infect humans if the crabs are eaten undercooked. These flukes aren't thought to occur in Europe, however.

Rainbow says the best time to catch the creatures is probably during their migration, when their numbers are most concentrated.

"This is also the best time to eat the crabs, because they are full of gonads—that's when the Chinese love them," he added.

But he suspects that baited traps, a common crab-catching method, wouldn't be as effective during migrating season.

"When they're going downstream food isn't important," he said. "Sex and getting to the estuary is more on their minds."

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