Chinese mitten crab
|Chinese mitten crab|
H. Milne-Edwards, 1853
|"Chinese mitten crab"|
|Alternative Chinese name|
The Chinese mitten crab (Eriocheir sinensis; Chinese: t 大閘蟹, s 大闸蟹, p dàzháxiè, lit. "big sluice crab"), also known as the Shanghai hairy crab (上海毛蟹, p Shànghǎi máoxiè), 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.
Description and ecology
This species' distinguishing features are the dense patches of dark setae on its claws. The crab's body is the size of a human palm. The carapace is 3–10 centimetres (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.
It moves from freshwater habitats to saltwater habitats once it has reached reproduction maturity. The types of estuaries suitable for the mitten crab is large brackish waters for the larva to develop in, and large shallow waters for the growth of the juvenile crabs.
This species has been spread rapidly from Asia (China and Korea) to North America and Europe, raising concerns that it competes with local species, and its burrowing nature damages embankments and clogs drainage systems. The crabs can make significant inland migrations. It was reported in 1995 that residents of Greenwich saw Chinese mitten crabs coming out of the River Thames, and in 2014 one was found in the Clyde, in Scotland. The crabs have also 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.
It is generally illegal to import, transport, or possess live Chinese mitten crabs in the United States, 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. California allows fishing for mitten crabs with some restrictions.
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.
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.
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. 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. 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. 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. 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. 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).
Management efforts have shown to be very difficult. This is due to its abundance, high reproductive rate, and high physiological tolerance. All the following efforts were attempted but showed little improvement: "catch as many as you can", migration barriers, trapping, raising awareness, electrical screens, and pulses.
- "Chinese mitten crab". The Washington Sea Grant Program. March 29, 2000.
- Stephen Gollasch (March 3, 2006). "Ecology of Eriocheir sinensis".
- Gollasch, Stephan (3 August 2009). "Eriocheir sinensis (Crustacean)". Global Invasive Species Database.
- "Exotic crabs in waterway invasion". BBC News. February 8, 2006.
- Elizabeth Williamson & David A. Fahrenthold (August 8, 2006). "Discovery of second invasive mitten crab raises worries". Washington Post.
- Invasion warning on Scotland's rivers, BBC News, 25 September 2014
- Greg Bruno (June 16, 2006). "Fishermen Fear a Mitten Crab Invasion". Times Herald-Record.
- "Title 50 – Wildlife and Fisheries. Part 16: Injurious Wildlife". Code of Federal Regulations. October 1, 2008.
- California Code of Regulations, Title 14, Section 671
- "Chinese Mitten Crab: Life and History". California Department of Fish and Game. August 5, 1998.
- P. D. N. Hebert. "Canada's Freshwater Invertebrates: Decapoda". Canada's Aquatic Environments. University of Guelph.
- "Chinese Mitten Crabs have come to the East Coast of the United States: We are seeking reports of mitten crab sightings and collections". Smithsonian Environmental Research Center. May 8, 2011.
- 3 September 2012, 中国大闸蟹入侵德国水域致德损失达8千万欧元 (Chinese mitten crabs invade German waters, cause damage of 80 million Euros), Sina News
- Dunlop, Fuchsia (15 December 2012). "The Chinese delicacy of hairy crabs". BBC News Magazine. Retrieved 15 December 2012.
- Keith Fitz-Gerald (November 17, 2010). "Record hairy crab prices point to China's continued strong economic growth next year". Seeking Alpha. Retrieved August 31, 2011.
- Clifford A. Hui, Deborah Rudnick & Erin Williams (2005). "Mercury burdens in Chinese mitten crabs (Eriocheir sinensis) in three tributaries of southern San Francisco Bay, California, USA". Environmental Pollution 133 (3): 481–487. doi:10.1016/j.envpol.2004.06.019. PMID 15519723.
- F. Silvestre, G. Trausch, A. Péqueux & P. Devos (2004). "Uptake of cadmium through isolated perfused gills of the Chinese mitten crab, Eriocheir sinensis". Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology 137 (1): 189–196. doi:10.1016/S1095-6433(03)00290-3.
- Associated Press Video
- Gizmodo "Vending Machine Sells Live Crabs"
|External identifiers for Eriocheir sinensis|
|Encyclopedia of Life||1024100|
- 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