Eat the Invading Alien Crabs, Urge U.K. Scientists

James Owen
for National Geographic News
November 13, 2003

In Asia it's considered a culinary delicacy. But in Britain, the Chinese mitten crab is seen as a dangerous alien that could cause lasting harm to the environment.

Scientists studying the furry-clawed crustacean, which is thought to have arrived from China as larvae in ballast water, now want people to eat the crabs into retreat.

The suggestion comes from zoologists at the Natural History Museum in London, England. Writing in the October Institute of Biology journal, the Biologist, Philip Rainbow and his team have called on commercial fishermen to target the species and send it back to where it came from.

Rainbow, the museum's keeper of zoology, said: "The Chinese love them, especially when they're full of gonads during the breeding season. The carapace of a large one measures eight centimeters (about three inches) across—that's a decent-sized meal."

Rainbow says the export of British-caught mitten crabs would help take the pressure off native plants and animals at risk from the advancing invaders. Mitten crabs are ravenous omnivores and the zoologists fear they could both eat and out-compete vulnerable freshwater species.

"It's quite a big crab and capable of disturbing the environment for other organisms," said Rainbow. "Because there isn't already a freshwater crab in Britain, species like the native crayfish, which is already in decline, are likely to be affected."

Studies show the crabs can also cause serious damage by burrowing into banks and earthworks along rivers. While sport fishermen in the London area say the crabs often hijack proceedings.

"You talk to any angling club on the tributaries of the River Thames and you find anglers really don't like them," Rainbow said. "The main problem is the general disturbance the crabs cause, such as worrying their bait—and now and again they'll reel one in that's hanging by its claws."

Ballast Water

First recorded in the River Thames in the 1930s, scientists believe the Chinese mitten crab (Eriocheir sinensis) arrived in Britain as tiny larvae in ballast water in ships from the Far East. Native to China and Korea, the species took a long time to become established, possibly because of the river's polluted state. Since the early 1990s, however, numbers have mushroomed. The crab, which can travel over dry land, has now spread to many other English rivers.

Rainbow said: "The population started to climb about ten years ago, then there was this snowballing effect, with more reproduction and more larvae."

He says numbers will probably level out eventually, but added, "There's a lot more available habitat before we reach that stage."

Continued on Next Page >>




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