Chinese mitten crab

Chinese mitten crab
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Infraorder:	Brachyura
Family:	Varunidae
Genus:	Eriocheir
Species:	E. sinensis
Binomial name
Eriocheir sinensis H. Milne-Edwards, 1853

The Chinese mitten crab, Eriocheir sinensis (also known as the big sluice crab (Chinese: 大閘蟹; pinyin: dà zhá xiè) and Shanghai hairy crab, Chinese: 上海毛蟹; pinyin: shànghǎi máo xiè) is a medium-sized burrowing crab that is named for its furry claws, which resemble mittens, and is native to the coastal estuaries of eastern Asia from Korea in the north to the Fujian province of China in the south. It has also been introduced to Europe and North America where it is considered an invasive species.^[1][2]

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 is 30–100 millimetres (1.2–3.9 in) wide, and the legs are about twice as long as the carapace is wide.

Mitten crabs spend most of their life in fresh water and 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 brackish 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.^[2]

Invasiveness

This species has been spread to North America and Europe, raising concerns that it competes with local species, and its burrowing nature damages embankments and clogs drainage systems.^[3][4] The crabs can make significant inland migrations. It was reported in the London Evening Standard in 1995 that the residents of Greenwich saw 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. In some places the crabs have been found hundreds of miles from the sea. There is concern in areas with a substantial native crab fishery, such as the Chesapeake Bay in Maryland and the Hudson River in New York (both locations where the crabs were first spotted in 2005), as the impact of the invasion by this species on the native population is unknown.^[5]

It is generally illegal to import, transport, or possess live Chinese mitten crabs in the United States,^[6] as accidental release or escape risks spreading these crabs to uninfested waters. In addition, some states may have their own restrictions on possession of mitten crabs.^[7] California allows fishing for mitten crabs with some restrictions.^[8]

The Chinese mitten crab has been introduced into the Great Lakes several times, but have not yet been able to establish a permanent population.^[9]

The Smithsonian is tracking the spread of the Chinese mitten crab and seeking help to determine the current distribution status of the mitten crab in the Chesapeake Bay region. People are encouraged to report any mitten crab sightings, along with details (date, specific location, size) and a close-up photograph or specimen if possible. The first confirmed record along the East coast of the United States, was in the Chesapeake Bay near Baltimore, Maryland in 2005.^[10]

Chinese mitten crabs have also invaded German waters, where they destroy fishing nets, hurt native fish species and damage local dams, causing damage of up to 80 million Euros. These crabs migrated from China to Europe as early as 1900, and were first documented by official German reports in 1922. After investigation by German scientists in 1933, it was thought that the crabs migrated to Europe through ballast water in commercial ships. The crabs are the only freshwater crab species in Germany, and their tendency to dig holes has caused damage to industrial infrastructure and dams.^[11]

Culinary

Hairy crab as Shanghai cuisine

The crab is an autumn delicacy in Shanghai cuisine and eastern China. It is prized for the female crab roe, which ripen in the ninth lunar month and the males in the tenth.^[12] The crab meat is believed by the Chinese to have a "cooling" (yin) effect on the body.

Chinese spend hundreds of yuan just to taste a small crab from Yangcheng Lake which are considered a delicacy. The crabs cost 680–700 yuan, or roughly US$105, per kilogram.^[13] 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 a new source of crab for the Chinese market. One proposed scheme involves importing unwanted crabs from Europe, where they are seen as a pest, to replenish local pure-bred stock.

Mitten crabs have exhibited a remarkable ability to survive in highly modified aquatic habitats, including polluted waters.^[2] Like some fish, they can also easily tolerate and uptake heavy metals, such as cadmium and mercury. Therefore, the farming and post-harvesting of the species needs proper management if it is used as a food.^[14][15] 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.

Recently, China introduced vending machines to sell this species of crab in the subways.^[16] The crabs are stored at 5 °C (41 °F), which induces a sleepy state of hibernation. The prices of the crabs range from around $1.50 to $7.00 (USD).^[17]

References

External links

• Media related to Eriocheir sinensis at Wikimedia Commons
• Species Profile – Chinese mitten crab (Eriocheir sinensis), National Invasive Species Information Center, United States National Agricultural Library
• Mitten Crab Watch - Smithsonian Environmental Research Center