Feeling Crabby?

Contact: Jonathan McKnight, Maryland Department of Natural Resources | 410-260-8539

Feeling Crabby?
Photo: Lee Mecum

ANNAPOLIS, MD (July 5, 2007) – A newly discovered invader from East Asia could make us all feel crabby, with its potential to do damage to the Chesapeake Bay ecosystem. The Chinese mitten crab (Eriocheir sinensis), in the first documented sighting on the East coast of the U.S., was found at the mouth of the Patapsco River a year ago. This crab, which divides its life cycle between fresh and saline water, and digs burrows in river banks, can weaken levees and destabilize banks, causing erosion. Huge numbers migrating together in California have clogged fish screens. The crab feeds on fish eggs and could affect trout spawning success. Six more crabs have been found since the first one, in both the Chesapeake and Delaware Bays, five in June 2007 alone, including the first mature female. If you are out crabbing, boating, or fishing in the Bay or its tributary streams, please look out for and report sightings of Chinese mitten crab, the MISC Invader of the Month for July.

The crab is distinctive, and can be identified by these features:

  • Hairy claws with white tips, about equal in size;
  • A notch between the eyes;
  • No swimming legs, but eight sharp-tipped walking legs more than twice as long as the body is wide;
  • Smooth round body shape (carapace) of light brown or olive green color;
  • Four lateral carapace spines (around the sides of the body, outside the eyes), the last one small;
  • Burrows with oval entrances between the low tide and mean high tide mark, especially in vertical clay banks;
  • Carapaces up to 4” wide.

Juvenile crabs may not have hairy claws if they are smaller than ¾” across the carapace, but they will have all the other features of the adults.

Originally from East Asia, the Chinese mitten crab is already a troublesome invader in both Europe and the West coast of the U.S.. Although it is illegal under the Lacey Act, to import or transport the animal, it may have been done. We do not know how this invader first arrived in Chesapeake waters.

The species is catadromous – it reproduces in salt water, and the juvenile crabs move upstream, as much as 50 miles inland, to live in fresh water for 2-5 years. Mature adults migrate downstream to mate and spawn in marine estuaries and then die.

Maryland DNR, the Smithsonian Environmental Research Center, US Fish and Wildlife Service, the National Oceanic and Air Administration and numerous local jurisdictions have formed a Network to find and remove this invasive animal threat. This Network is asking citizens to report these crabs wherever they are found. If you find what you think is a Chinese mitten crab, DO NOT THROW IT BACK ALIVE into the water. Freeze the crab, or keep it on ice, or as a last resort, preserve it in rubbing alcohol. Take note of the precise location where it was found. If possible, take a close-up photo, either film or digital, that shows the identifying characteristics well. If you cannot take a photo, call the Mitten Crab Hotline at 443.482.2222. Digital photos may be emailed to: SERCMittenCrab@si.edu. Do not transport Chinese mitten crabs, except to deliver them to an appropriate official.

For more information about other Invasive Species of Concern, visit the Maryland Invasive Species Council.

For more information on the Internet:

The Marine Invasions Research Lab

The Maryland Department of Natural Resources