Eriocheir sinensis (Chinese Mitten Crab) is a catadromous crab, which spawns in estuaries of northern China and Korea. The planktonic larvae require salinities of 15-30 ppt for successful development to the megalopa stage, and show their best survival at 25 ppt Megalopae show a preference for intermediate salinities of 15-25 ppt, and tend to seek bottom waters, resulting in upstream transport (Anger 1991). Juvenile crabs seek out freshwater and migrate up rivers, up to 1000 km upstream while growing to adult size. Time to maturation ranges from 1 to 3 years in China and 3-5 years in Europe (Herborg et al. 2005). Adult crabs are tolerant of a wide range of salinities and temperatures, growing actively at temperatures from 7 to 30 C (Anger 1991; Rudnick et al. 2000). Adult crabs migrate downstream for spawning (in Europe in late fall), the males first, followed by the females. Not all crabs may migrate upstream- some may stay in brackish water (Rudnick et al. 2000).
The estuarine breeding habitat, long planktonic larval stage, wide environmental tolerances, and long-distance migrations of the Chinese Mitten Crab all seem to have contributed to its success as an invader. Eriocheir sinensis was first collected outside its native range in the Aller River, Germany, a North Sea tributary, and soon spread to the nearby Elbe River. No further range expansions was reported until 1927, but from 1927 to 1954, the crab spread rapidly westward along the North Sea and English Channel coast, reaching St. Malo, Normandy, France in 1954, but also, in 1954, appearing in the Gironde and Loire estuaries, on the Bay of Biscay. By 1958, it was collected at Hendaye, France, on the border with Spain (Herborg et al. 2005). By 1999, it reached the Tagus River, Portugal (Cabral and Costa 1999). The Chinese Mitten Crab also spread rapidly to the East, reaching Vyborg at the head of the Gulf of Finland by 1933 and Gaevle, Sweden, in the lower Gulf of Bothnia by 1934. Peak rates of spread in European waters exceeded 500 km/year, but over longer periods, more typically averaged 100-200 km/year (Herborg et al. 2005). Aside for a couple of individual captures in 1935 and 1949, the establishment and spread of E. sinensis in the British Isle began in the river Thames in 1973. The crab continues to spread, reaching the Tyne River, Yorkshire (North Sea Coast) and the Irish Sea coast (Wales) by 2001. Canals have enabled E. sinensis to move between river systems inland, as well as along the coast (Herborg et al. 2005).
Canal systems and ballast water transport have enabled Eriocheir sinensis to reach outlying bodies of water in Eurasia, including rivers and lakes in landlocked countries such as the Czech Republic, Austria, Switzerland and Hungary (Herborg et al. 2003). In 1960, several specimens of this crab were found in Mediterranean lagoons in the vicinity of Narbonne, France. The crabs had probably reached the Mediterranean by the Canal du Midi. However, this population did not become established (Galil et al. 2002). In 1998, E. sinensis was collected in the Gulf of Odessa, on the Black Sea, where a population is now established and has been collected from inland sites in the Volga River basin, and in the Sea of Azov (Murina and Antonovsky 2001; Gomiou et al. 2002). A specimen has also been collected from a freshwater river near the Caspian Sea, in Iran, in 2001 (Robbins et al. 2006). Another single specimen was collected from a brackish canal feeding into the Persian Gulf, in Basra, Iraq (Clark et al. 2006b). Chinese Mitten Crabs are now regularly caught in the Archangel Bay, of the White Sea (Berger and Naumov 2002). Canals connecting to the Baltic are a likely vector for the Black, White Sea, and Caspian Sea populations, but the Iraq specimen was probably a ballast water introduction. Two specimens collected in Tokyo Harbor in 2004 represent a probable introduction of E. sinensis to Japan from China (Takeda and Koziumi 2005), either by ballast water, or as a fisheries-related release.
Great Lakes-St. Lawrence River- The first North American specimens of Eriocheir sinensis were caught in the Great Lakes, beginning in 1965, when a crab was found in a water-intake pipe on the Detroit River, at Windsor, Ontario In 1973, three more specimens were caught in gill nets in Lake Erie. These crabs were probably brought from the Baltic in ships' ballast water (Nepszy and Leach 1973). Additional Great Lakes specimens were collected in 2005-2007, two in Lake Superior, at Thunder Bay and three in Lake Erie (Center for Aquatic Resource Studies 2006; de LaFontaine 2008). In 2004, two specimens were caught in the St. Lawrence River, the first near Quebec City, and a second near Trois Rivieres, both in the estuary in 2004, and a third in 2005, in Lake St. Pierre, in a dammed portion of the river, above the head of tide (de Lafontaine 2005; Environment Canada 2006). In 2006-2007, eight additonal adult specimens were caught in the St. Lawrence estuary (de Lafontaine 2008). Reproduction of E. sinensis in the St. Lawrence River has not been documented.
Gulf of Mexico drainage- A single specimen of E. sinensis was collected from the Mississippi River Delta in Plaquemines Parish Louisiana (Center for Aquatic Resource Studies 2006). This specimen could have arrived by ballast water or be an escape or release resulting from the "live food" trade.
San Francisco Bay- The only known established population of Eriocheir sinensis in the United States is in the San Francisco Bay estuary and watershed. Fishermen had reported first catching Mitten Crabs in the Bay in 1992. By 1996, they had been collected in the north (San Pablo Bay, Suisun Bay) and south (South Bay) arms of the estuary and their freshwater tributaries (Cohen and Carlton 1997). By 2000, crabs had been collected throughout the Bay, and through much of the lower San Francisco Bay drainage, up to 300 km from tidal waters. Crab burrows in 1999-2000 in South Bay tributaries averaged 20-30/m2, and catches of adult crabs in 1998-2000 reached 100,000-800,000 crabs per year in different regions of the Bay (Rudnick et al. 2003). So far, on the West Coast, E. sinensis is known only from the San Francisco Bay estuary and watershed. A single crab caught in the Columbia River, near Astoria OR in 1997, has been identified as E. japonica (Jensen and Armstrong 2005).
In June 2006, John Delp, a waterman, aboard the crab boat Bodacious, caught a single adult male specimen of Eriocheir sinensis at Seven-foot Knoll, adjacent to the channel at the mouth of the Patpasco River, at the entrance to Baltimore Harbor (John Delp, personal communication, Lynn Fegley (7/21/06, personal communication); The specimen was given to personnel at the Maryland Department of Natural Resources and was then brought to the Smithsonian Environmental Research Center (SERC). The specimen was tentatively identified as a male E. sinensis by Yongxu Cheng (7/21/06, personal communication). Rafael LeMaitre (U.S. National Museum of Natural History) confirmed this identification by comparing the specimen to one collected in China.
The publicity about this crab's capture resulted in a report of an earlier male specimen, caught in or before June 2005, by Jim Foltz, a watermen, in Chesapeake Bay, between Fort Howard and North Point, just outside the mouth of the Patapsco River. This specimen, also a male, was kept alive in an aquarium for several months by Steve Thaos, a ranger at North Point State Park, who then froze it and kept it. The specimen was given to the Smithsonan Environmental Research Center (Jim Foltz, Steve Thaos, Carin Stringer, personal communications; Ruiz et al. 2006). In 2006, the SERC Invasions Group recieved 2 additional reports of captures of Mitten Crabs, one near Chesapeake Beach MD, and another at the mouth of the Patuxent River near Solomons. While we did not receive specimens, we considered these reports to be reliable (Ruiz et al. 2006). On May 18 2007, an additional adult male specimen was collected at Holland Point Bar, Chesapeake Beach MD, and in June, two adult female specimens, the first in Chesapeake Bay, were collected, one at Bloody Point Light, on Kent Island, MD, and the other at Cove Point, Solomons MD. In June, 2009, one was caught in North Point Creek near Dundalk MD. So far, all the crabs collected and examined in Chesapeake Bay have been adults, 62-66 mm carapace diameter, 4 males and 2 females. One of the female crab appeared to be in the process of developing a second brood of eggs.
In late May 2007, Mitten Crabs were caught in two locations in upper Delaware Bay, at Liston Point (May 25, 1 male) and Woodland Beach DE (May 29-30, 3 males) (Center for Aquatic Resource Studies 2007, Carin Ferrante, personal communication). On July 11, a female crab was caught at Silver Bed Oyster Bar, in the Simons River, DE ). This female had spawned once, and was bearing a second brood of fertilized eggs (Center for Aquatic Resource Studies 2007, Carin Ferrante, personal communication. In 2009, 5 additional adults, 2 female and 3 males were caught in upper Delaware Bay (Darrick Sparks, personal communication). However, there are no reports of this crab in Chesapeake Bay waters since 2009.
Hudson River Estuary- On June 3, 2007, an adult male Mitten Crab was caught near the Tappan Zee Bridge, in Nyack NY (Center for Aquatic Resource Studies 2007, Carin Ferrante and Darrick Sparks personal communication). Starting in October 2007, 35 crabs, 16-70 mm in carapace width, have been caught in tidal fresh portions to marine ortions of the river between New York Harbor and Tivoli, New York (Carin Ferrante, personal communication). Some juveniles were caught near dams and falls of tributaries, locations suggesting migration. The occurrence oflarge numbers of molts of juvenile crabs indicates the establishment of Mitten Crabs in ths estuary (Schmidt et al. 2009).
In June 2008, two adult male crabs were caught in coastal bays of New Jersey, one in Raritan Bay, a subestuary of New York Bight, into which the Hudson also flows. From May to September, 2009, 36 adult crabs, 18 males, 18 females (4 bearing eggs) were caught in Raritan Bay and its tributaries.
New Jersey Coastal Bays-One male crab was caught in Toms River NJ, in a tributary of Barnegat Bay (Carin Ferrante, personal communication). A second adult male crab was caught in May 2009 in Barnegat Bay (Darrick sparks, personal communication).
From 2006 through September 2009, 93 Chinese Mitten Crabs, 36 females and 57 males, ranging from 16 to 74 mm carapace width have been collected in the mid-Atlantic region of the US, from Chesapeake Bay north to the Hudson River. . Reproduction has not been confirmed, but the increasing captures of juveniles increase the probability of establishment of this species.
The importation of Eriocheir sinensis to North America, and interstate transport is prohibited by the federal Lacey Act. Mitten crabs were listed under the act in 1989. Before then, they were offered alive for sale in Asian markets at prices up to $32/kg. In 1987, they were also banned by California state law (Cohen and Carlton 1998). Maryland banned possession of Chinese Mitten Crabs in 2002 (Maryland Department of Natural Resources 2006.
Invasion References: Anger 1991; Berger and Naumov 2002; Cabral and Costa 1999; Center for Aquatic Resource Studies 2006-2007; Cohen and Carlton 1997; de Lafontaine 2005; Environment Canada 2006; Galil et al. 2002; Gomiou et al. 2002; Herborg et al. 2003; Herborg et al. 2005; Jensen and Armstrong 2005; Maryland Department of Natural Resources 2006; Murina and Antonovsky 2001; Nepsy and Leach 1973; Robbins et al. 2006; Rudnick et al. 2000; Rudnick et a. 2003; Ruiz et al. 2006; Takeda and Koziumi 2005;