Thursday, September 18, 2008

Chinese mitten crab

Chinese mitten crab, ''Eriocheir sinensis'', also known as the big binding crab and Shanghai hairy crab , is a medium-sized burrowing crab that is native in the coastal of eastern Asia from Korea in the north to the Fujian province of China in the south, but migrated to Europe and North-America.

Formerly in the Grapsidae, it is now placed in the Varunidae.

Description and ecology

This species' distinguishing features are the dense patches of dark hair on its claws. The crab's body is the size of a human palm. The carapace width is 30–100  and the legs are about twice as long as the carapace is wide.

Mitten crabs spend most of their life in fresh water, but they must return to the sea to breed. During their fourth or fifth year in late summer, the crustaceans migrate downstream, and attain sexual maturity in the tidal estuaries. After mating, the females continue seaward, overwintering in deeper waters. They return to water in the spring to hatch their eggs. After development as larvae, the juvenile crabs gradually move upstream into fresh water, thus completing the life cycle. The crabs can make significant inland migrations. It was reported in the London Evening Standard in 1995 that the residents of Greenwich, UK, saw the Chinese mitten crabs coming out of the River Thames and moving towards the High Street, and other reports indicate that the crabs have been known to take up residence in swimming pools. There is especial concern in areas with a substantial native crab fishery, such as the Chesapeake Bay in Maryland and the Hudson River in New York , as the impact of the invasion by this species on the native population is unknown.


In contrast, the crab is a famous delicacy in Shanghai cuisine and is prized for the female crab's ovaries. The crab meat is believed by the Chinese to have a "cooling" effect on the body. Concerns have been raised that the population and origin of the crab may be affected because of overfishing of the species in the Yangtze River. Today Yangcheng Lake is the most famous area for the Chinese mitten crabs, however, the original species had been extirpated by the early 1990s. All you can find in Yangcheng Lake nowadays is a Japanese relative that was introduced around 2000.

Chinese spend hundreds of just to taste a small crab from that lake. But even these are in fact the more robust Japanese mitten crabs, as the original native stock in Yangcheng Lake has disappeared. Most of the Yangcheng crabs are exported to Shanghai and Hong Kong, and high-profit foreign markets. Responding to the spread of the crab to the West, businessmen have started seeing it as the new source of crab for supporting the huge appetite in China market. One proposed scheme involves importing unwanted crabs from Europe, where they are seen as a pest, to replenish local pure-bred stock.

The mitten crabs had exhibited a remarkable ability to survive in highly modified aquatic habitats, including polluted waters.

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