Invasive, spider-like crab discovered in Greenwich
Updated 9:53 pm, Friday, August 3, 2012
Connecticut's first documented specimen of a highly invasive crab species native to eastern Asia was found at the end of June in Greenwich's Mianus Pond fishway.
The Department of Energy and Environmental Protection has confirmed that Joe Cassone, conservation assistant for the town, collected a juvenile Chinese mitten crab from the fishway, located on the Mianus River.
First delivered to DEEP's Marine Headquarters in Old Lyme and examined by DEEP and a Connecticut Sea Grant biologist, the creature was sent to the Marine Invasion Research Lab of the Smithsonian Environmental Research Center in California for a confirmation of identification.
David Molnar, marine fisheries biologist with DEEP, said the crab, considered a delicacy in Eastern Asia, has fuzzy growth on its claws, which have whitish tips. It's the only crab that could be found in fresh water in the Northeast.
"When you look at them, they look like a giant spider," Molnar said.
This particular crab measured 2.5 inches across its shell and 6 inches including legs. Mature crabs can measure 12 inches across, including legs.
When asked how the Greenwich crab got into Connecticut waters, Molnar replied, "That's a good question."
The crab was likely headed upriver and may have come from the Hudson River, where Molnar believes mitten crabs are reproducing. A mitten crab was discovered last year in the Hudson River near the Tappan Zee Bridge, he said.
As to mitten crabs' effects on local ecosystems, Molnar still isn't sure how the animals might fit in.
"It's too early to tell," he said.
In high densities, the 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, according to DEEP.
"Early detection of new species in our marine or fresh waters can help lead to more options for control and spread prevention," she said. "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."
The crabs spend much of their life in fresh water and then migrate to estuarine and marine waters in late summer or fall to spawn, according to DEEP. A female can produce up to 1 million eggs.
Though the creatures -- which have smooth brownish to greenish shells with spines and a notch between the eyes -- are native to eastern Asia, they have spread to Europe and North America. In Europe, the first mitten crab was discovered in Germany in the early 1900s, and the population has since expanded throughout a number of waterways in northern and central Europe, most recently becoming established in the Thames River in England.
The crabs first appeared in the United States on the Pacific coast in 1992 and now have a well-established population throughout the San Francisco Bay estuary system. First found along the Atlantic coast in 2005, a number of crabs have turned up in the Chesapeake and Delaware bays and several New Jersey estuaries, in addition to the Hudson River. The two most likely means of introduction to local waters are transportation in ship ballast water and deliberate release to establish a fishery or local food resource.
Importation and interstate transport of mitten crabs are prohibited under the Federal Lacey Act.
Anyone who finds a crab suspected to be a Chinese mitten should keep it on ice or freeze it, note the exact location where it was found, and contact DEEP Marine Fisheries (860-434-6043), DEEP Inland Fisheries (860-424-3474), or CT Sea Grant (860-407-9107).