First Non-native North American Marine/Estuarine Record: 1992
First Non-native West Coast Marine/Estuarine Record: 1992
First Non-native East/Gulf Coast Marine/Estuarine Record: 2004
The Chinese Mitten Crab, Eriocheir sinensis, is native to China from the Bohai Sea and the southern coast of South Korea, south to Macau, near Hong Kong (Guo et al. 1997). This crab is catadromous, breeding in brackish-to-marine waters in estuaries and coastal waters, and moving upstream as a juvenile to mature in fresh waters, up to 1000 km from the sea. Adult crabs then migrate back to the mouths of estuaries for spawning (Guo et al. 1997; Panning 1939; 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 introduced to Europe, most likely in ballast water, and was first discovered in Germany in 1912. It has spread throughout much of Europe by canals and shipping, ranging from the Atlantic coast of Spain to Sweden and Finland (Herborg et al. 2003). It has appeared sporadically in the Mediterranean, Caspian and White Seas, and is established in the Black Sea (Berger et al. 2002; Galil et al. 2002; Gomiou et al. 2002; Robbins et al. 2006). In North America, it has been collected in the Great Lakes since 1965 (Nepszy and Leach 1973), and since 2004, from the St. Lawrence River (de Lafontaine et al. 2008). In 2005, a Chinese Mitten Crab was caught in Chesapeake Bay. Since then it has been found in the Delaware Bay, coastal bays of New Jersey, and the Hudson River estuary. So far, evidence of breeding (gravid females, juveniles, molts of juveniles) has been found only in the Hudson River- the crabs in other estuaries have all been adults (Ruiz et al. 2006; Schmidt et al. 2009; Ruiz et al. unpublished). On the other side of the continent, E. sinensis was first caught in San Francisco Bay in 1992, and has spread through much of the Bay's watershed, up to 300 km from the Bay itself (Cohen and Carlton 1997; Rudnick et al. 2003).
The only known established population of Eriocheir sinensis on the West Coast is from the San Francisco Bay estuary and watershed. Fishermen first reported 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). Variation in abundance of larvae and recruitment of juveniles appears to vary greatly among years, and appears to be most strongly affected by temperature during the spawning season, which occurs in winter (Blumenshine et al. 2011). A single crab caught in the Columbia River, near Astoria, Oregon, in 1997, was identified as E. japonica (Jensen and Armstrong 2004).
Mitten Crabs were abundant at the Tracy Fish Collection Facility in Byron, CA every year from 1996 to 2005, but only single individuals were observed in 2006, 2009, and 2010. No crabs have been observed in California since 2010 (Steve Foss, personal communication (3/28/18). The absence of recent records is paralleled both on the East and West Coasts, but it is possible that populations are persisting at low levels of abundance. For now, we will treat the population as established.
Chesapeake Bay- 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 then brought to the Smithsonian Environmental Research Center. It 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.
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 waterman, 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 Smithsonian Environmental Research Center (SERC) (Jim Foltz, Steve Thaos, Carin Ferrante, personal communications; Ruiz et al. 2006). In 2006, the SERC Invasions Lab received two additional reports of captures of Mitten Crabs, one near Chesapeake Beach, Maryland, and another at the mouth of the Patuxent River near Solomons, Maryland. 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 was collected at Holland Point Bar, Chesapeake Beach, and in June, two adult females, the first in Chesapeake Bay, were collected, one at Bloody Point Light, on Kent Island, Maryland, and the other at Cove Point, Solomons. In 2009, an adult male crab was captured at North Point Creek (Carin Ferrante, Darrick Sparks, personal communications). So far, all of the crabs collected and examined in Chesapeake Bay have been adults with a 62-66 mm carapace diameter. One of the female crabs appeared to be in the process of developing a second brood of eggs. No mitten crabs have been collected in Chesapeake Bay since 2009, and there is no evidence of an established population at this time (May 2011).
Delaware Bay- In late May 2007, Mitten Crabs were caught in two locations in upper Delaware Bay, at Liston Point (May 25, one male) and Woodland Beach (May 29-30, three 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, Delaware. This female had spawned once, and was bearing a second brood of fertilized eggs (Center for Aquatic Resource Studies 2007, Carin Ferrante, personal communication). As of May 2011, 16 adult mitten crabs have been collected in brackish waters of Delaware Bay. No juvenile crabs have been collected, and there is no evidence of a breeding population (Carin Ferrante, Darrick Sparks, personal communication).
New Jersey Coastal Bays- In June 2008, an adult male crab was caught in Toms River, New Jersey, a tributary of Barnegat Bay (Carin Ferrante, personal communication). Two female crabs were also caught in Toms River, one in May 2008 and one in May 2009. In 2010, a male crab was caught in Barnegat Bay, at Seaside Park. To the north of Barnegat Bay, a female crab was caught in the Manasquan River in October 2009. In Great Egg Harbor, to the south, a male crab was collected at Ocean City in May 2010 (Darrick Sparks, personal communication). Again, no juvenile crabs have been collected, and there is no evidence of a breeding population.
Hudson River Estuary and Raritan Bay- 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, personal communication). Starting in October 2007, 115 total crabs, including juveniles as small as 16 mm in carapace width, males, and egg-bearing females have been caught in tidal portions of the river from near Albany, New York to New York Harbor. Some were caught near dams and falls of tributaries, which suggests migration (Carin Ferrante; Darrick Sparks, personal communication), and a number of molted carapaces have been seen in several tributary streams (Schmidt et al. 2009). In June 2008, a male crab was caught in Raritan Bay, a sub-estuary of the New York Bight, into which the Hudson River also flows. In 2009, 39 crabs, including several adult females, were caught in Raritan Bay and its tributaries. Since Chinese Mitten Crabs have not been caught in the freshwaters of the Raritan River system, the Raritan crabs appear to be an offshoot of the breeding population in the Hudson River (Carin Ferrante; Darrick Sparks, personal communication). In January 2010, 21 adult crabs, one male and 20 gravid adult females were trawled in New York Harbor.
Since 2006, 165 Chinese Mitten Crabs (number as of May 2011), have been collected in the mid-Atlantic region of the US, from Chesapeake Bay north to the Hudson River. In the Hudson River, the occurrence of gravid females in the higher-salinity parts of the estuary, and molting juveniles in freshwater streams supports the presence of a breeding, migratory population (Schmidt et 2009, Carin Ferrante; Darrick Sparks, personal communication; Ruiz et al., unpublished data). Occurrences in estuaries to the south may represent an outflow of larvae from the Hudson, or could indicate the presence of undiscovered reproducing populations.
Long Island Sound- Two specimens of E. sinensis were caught in the Mianus Pond fishway in Greenwich, Connecticut, on June 20 2012 and October 30 2014. The fishway is just above the tidal river. The first specimen was a young crab, missing claws and the second was an adult female (Darrick Sparks, personal communication, USGS Nonindigenous Aquatic Species Program 2013; Matthew Goclowski 10/30/2014).
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, in Lake Superior, at Thunder Bay, and in Lake Erie (Center for Aquatic Resource Studies 2006). In 2004, several specimens were caught in the St. Lawrence River, the first near Quebec City, a second near Trois Rivieres, and a third in Lake St. Pierre, in a dammed portion of the river, above the head of the tide (de Lafontaine 2005; Environment Canada 2006). Reproduction of E. sinensis in the St Lawrence River has not been documented.
Mitten Crabs probably reached the Great Lakes by ballast water from Europe, and ballast water transport is a possible vector for other introduction locations on the East Coast. Another potential vector is the importation of live crabs for food, as they are considered a delicacy in Asian communities. The importation and inter-state transport of Eriocheir sinensis in North America is prohibited by the federal Lacey Act. Mitten crabs were listed under the act in 1989. Prior to being listed, they were sold alive in Asian markets at prices up to $32/kg. In 1987, they were also banned by California state law (Cohen and Carlton 1997). Maryland banned possession of Chinese Mitten Crabs in 2002 (Maryland Department of Natural Resources 2006).
In 1987, a single specimen of Eriocheir 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.
Eriocheir sinensis was first collected outside its native range in 1912 in the Aller River, Germany, a North Sea tributary, and soon spread to the nearby Elbe River. No further range expansions were reported until 1927, but from 1927 to 1954, E. sinensis spread rapidly westward along the North Sea and English Channel coasts, 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. In the Baltic, spawning populations have been found as far east as Kiel Bight (Otto and Brandis 2011), but the frequent occurrence of crabs far into the inner Baltic suggests either migrations of up to 1000 km, or spawning at lower salinities (Ojaveer et al. 2007). 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 from a couple of individual captures in 1935 and 1949, the establishment and spread of E. sinensis in the British Isles began in the river Thames in 1973. The crab continued 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). A single specimen, collected from a brackish canal feeding into the Persian Gulf, in Basra, Iraq (Clark et al. 2006), has been re-identified as E. hepuensis (Naser et al. 2012). 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 Iraqi 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.