Mitten crab from Chesapeake may indicate
an expanding East Coast Population

"Looks like a big weird spider," Maryland waterman John Delp recalled thinking to himself as he hauled up a strange-looking crab in June 2006 at the mouth of the Patapsco River in the Chesapeake Bay.

He froze the creature and later, at the Smithsonian Environmental Research Center in Edgewater, Md., it was positively identified as a Chinese mitten crab--so called because its claws are covered with tiny setae, or hairs. Scientific name: Eriocheir sinensis.

Scientists were alarmed. Was this an isolated individual or one from a previously undetected population of mitten crabs now living and expanding in the bay?

Native to Korea and China, thousands of tons of mitten crabs are harvested in Asia each year for food. Delp’s catch, however, was the first of this invasive species to be reported in the Chesapeake. Following local news coverage of the crab, a second specimen was turned in by a local waterman and confirmed to be a mitten crab.

On the West Coast, a single mitten crab was found in San Francisco Bay in 1992. Today, their range has expanded throughout hundreds of miles of the San Francisco Bay and its tributaries.

Digging into stream banks, damaging fishing nets, clogging water pumps and eating native vegetation, mitten crabs have become a serious pest in the San Francisco area. For the Chesapeake and its watershed, the crab may pose the same threat, says SERC Ecologist Greg Ruiz.

"We are now working with the Maryland Department of Natural Resources to conduct further surveys and monitor the upper Chesapeake and its tributaries," says SERC Director Tuck Hines. Yongxu Cheng, a visiting researcher at SERC who happens to be an expert in mitten crab biology and culture from Shanghai Fisheries University in China, also is consulting on the project.

How Delp’s mitten crab arrived in the United States is a mystery. Scientists suspect it may have arrived as planktonic larva in the ballast water of a cargo ship.

This theory is supported by the fact that the busy Port of Baltimore is on the Patapsco River. It also may have been smuggled into this country from Asia.

For now, Delp’s crab is in a jar of alcohol in the invertebrate collections of the Smithsonian’s National Museum of Natural History in Washington, D.C. An alert has been issued to Chesapeake Bay watermen for any other catches of mitten crabs. Should more mitten crabs be pulled from the Chesapeake, DNA taken from these first specimens can help determine if the crabs are related and possibly initial members of an expanding East Coast population.