The Department of Energy and Environmental Protection (DEEP) and Connecticut Sea Grant today confirmed that a juvenile Chinese mitten crab (Eriocheir sinensis) has been found in Connecticut waters. In late June, the crab was collected from the Mianus Pond fishway on the Mianus River (Greenwich) by Joe Cassone, Conservation Assistant for the Town of Greenwich Conservation Commission. The crab was first delivered to DEEP’s Marine Headquarters in Old Lyme, and following examination by DEEP and CT Sea Grant biologists, sent to the Marine Invasion Research Lab of the Smithsonian Environmental Research Center for a confirmation of the initial identification.

“This discovery is of some concern,” said DEEP Deputy Commissioner Susan Frechette. “In high densities, these crabs can damage fishing gear, clog pumps and intake pipes, cause riverbank erosion through their burrowing activities and outcompete native species for food and habitat. However, these crabs are relatively new to the Atlantic coast, and at this time it is unclear as to what their effects will actually be.”

%pullstart%The Chinese mitten crab is native to eastern Asia, but has spread to both Europe and North America.%pullend%Chinese mitten crabs were first found in North America on the U.S. Pacific coast in 1992 and now have a well established population throughout the San Francisco Bay estuary system, including the Sacramento and San Joaquin rivers and a number of smaller rivers flowing into the bay. First found along the Atlantic coast in 2005, a number of individuals have been found in Chesapeake Bay, Delaware Bay, several New Jersey estuaries and the Hudson River. The two most likely means of introduction appear to be transport of larvae and small crabs in ship ballast water and deliberate release to establish a fishery or local food resource (in its native range, this crab is considered a delicacy). Under the Federal Lacey Act, importation and interstate transport of this animal is prohibited.

Unlike other crabs found in North America, these crabs spend much of their life in fresh water. Chinese mitten crabs are catadromous; sub-adults live in freshwater for 1-4 years and then migrate to estuarine/marine waters (typically in late summer or the fall), where they reach maturity and spawn. Each female can produce 100,000 to 1,000,000 eggs, which are carried until they hatch in late winter. The larvae remain in the water column for 1-2 months before settling and developing into juvenile crabs. In late spring/early summer the juveniles begin moving upstream into brackish and then fresh water. These crabs cannot swim, but are adept at walking, and on land they can walk around obstacles.

“It’s important that people keep an eye out for these crabs and report them,” says Nancy Balcom, Associate Director of Connecticut Sea Grant at the University of Connecticut. “Early detection of new species in our marine or fresh waters can help lead to more options for control and spread prevention. In 2010, there was a reported sighting of a crab in a pond near the Mill River in Fairfield that may have been a mitten crab. Unfortunately, we were unable to catch that crab to confirm its identification.”

Chinese mitten crabs claws are of equal size; all but the very smallest (<1 inch shell width) appear to have dark fuzzy growth on the claws with whitish tips (hence the name “mitten crab”). The smooth shell or carapace is brownish to greenish, up to approximately four inches across, with four spines on each side and a notch between the eyes. Total crab size, including legs, can be up to 12 inches. Individuals finding a crab that they suspect to be a Chinese mitten crab should keep the crab on ice or freeze it (please do not release the crab), note the exact location it was found, and contact DEEP Marine Fisheries (860-434-6043), DEEP Inland Fisheries (860-424-3474) or CT Sea Grant (Nancy Balcom, 860-407-9107). Any crab found in fresh water should be investigated, as there are no freshwater crabs in New England.