Feature Story                                                                 May 2011

Citizen Science: New Website Launched Making it Easier to
Reports Sightings of Chinese Mitten Crabs

A Chinese Mitten Crab caught in Chesapeake Bay

Are you a crabber, waterman, or concerned citizen? We need your help to detect and assess the status of Chinese Mitten Crabs (Eriocheir sinensis) along the Atlantic and the Gulf Coasts. Recently a new website has been launched to provide information on the invasion of the mitten crab and to allow users to more easily report catches.

Chinese Mitten Crabs are native to East Asia and are an established invader in Europe and United States. In the United States, mitten crabs have established populations in San Francisco Bay and along the mid-Atlantic Coast, being reported from Maryland to New York. This crab has also been reported in Great Lakes and Gulf Coast, but does not appear to be established there.

Mitten Crabs can have economic and ecological impacts in their introduced range, especially during periods of high abundance. In San Francisco Bay, the crabs impaired the operation of passage facilities designed to help in fish migration, causing the loss of thousands of fish. The crabs also can increase erosion by burrowing and thereby reduce the structural integrity of banks and levees

Effects of mitten crabs on the East Coast are not yet known, because this is a relatively recent invasion and has not been studied. The first confirmed record on the East Coast was in 2005, a crab was caught by a commercial crabber in the Chesapeake Bay near Baltimore, Maryland.

Mitten crabs can be found in both freshwater and saltwater environments. The crabs are catadroumous, meaning their breeding and migration patterns are the exact opposite of salmon. Rather than going upstream to breed, these crabs go downstream to the estuary to breed. The migration of adults from freshwater streams into saltwater estuaries occurs in the late winter. Their larvae hatch from eggs and develop in marine environments during the spring and summer. Juvenile crabs migrate into freshwater tributaries where they live for two to five years before returning to the estuaries to breed.

As this year’s crabbing season begins, you may see breeding adults in the estuaries and younger adults and juveniles in the freshwater tributaries. In the Atlantic and Gulf Coast regions, native crabs are rare in freshwater, so if you see a crab upriver, chances are very good that it’s a Chinese Mitten Crab.

We are asking anyone who catches a mitten crab to keep the crab (don’t throw it back alive), photograph it, and send us a report with the photograph (and/or specimen) and the location and date of your catch. Reporting your catch and uploading your photos is easy on our new website - http://mittencrab.nisbase.org/ - just log in and go to the tab "My Crabs" to submit a report. These reports will help us understand the extent of the mitten crab invasion and will help in control efforts. If you have any questions please send us an email at SERCMittenCrab@si.edu.

Chinese Mitten Crab (Eriocheir sinensis) showing three identifying features.1) Four lateral spines, 2) a notch between the eyes, and 3) furry claws.