The "What" and the "Why"

The "What" and the "Why"

What are we trying to learn?

Chinese Mitten Crab
A Chinese Mitten Crab showing its key identifying features- furry claws, a central notch, and four spines located on each side of the carapace.


We are trying to figure out where Chinese Mitten Crabs are along the Atlantic Coast of North America. The Chinese Mitten Crab (Eriocher sinensis) is native to East Asia and is considered an established invader in Europe and the United States. The first established US population was in California's San Francisco Bay and Delta in the 1980s. Between 1998 and 2000, catches reached 100,000 - 800,00 crabs per year in some part of San Francisco Bay but has gone undetected since 2010. the first confirmed record of Chinese Mitten Crabs in the Mid-Atlantic was from Baltimore, Maryland in 2005. Between 2005 and 2014 crabs were reported in the US Mid- Atlantic from Maryland to Connecticut. Mitten crabs have also been found sporadically in the Great Lakes and the US Gulf Coast, but haven't established a breeding population in either region.

Spurred by the initial Chesapeake Bay report in 2005, we launched an online tracking system called Mitten Crab Watch ( and hotline (443-482-2222), and received new reports of Chinese Mitten Crabs throughout the U.S. Mid-Atlantic region, especially from Maryland to New York. In the early years of Mitten Crab Watch, we confirmed over 150 reports from commercial and recreational fisherman along the eastern U.S., with most from the Hudson River in New York. These public-sourced reports confirmed the first Chinese Mitten Crabs breeding population for the eastern U.S., but the last record of a live crab for the region is from Chesapeake Bay in 2014. Similarly, no crabs have been reported in California since 2010. The absence of recent records on the East and West Coasts is puzzling. Are the crabs now gone from the U.S. east or west coast?  Or, are they just in low abundance and hard to detect? We need your help to solve this mystery!

Why do we care about Chinese Mitten Crabs?

Chinese Mitten Crabs have been listed as one of the '100 worst invasive species' by the Invasive Species Specialist Group of the World Conservation Union (IUCN).

These crabs have a long planktonic stage, suggesting that ballast water (water held in the ballast tanks and cargo holds of ships- used to provide stability and maneuverability during a voyage) is most likely how these organisms were introduced in certain areas but some populations may also have been introduced through "live trade". Sometimes a new, introduced organism does not survive in the environment but other times they survive and become invasive species. Invasive species are living outside of their native range, moved by the assistance of humans and cause ecological or economic harm. (Learn more about the difference between non-native, introduced, and invasive species here). Invasive species can have major impacts on ecosystems and Chinese Mitten Crabs are no exceptions. Mitten crabs threatened to collapse river banks with their burrows and made fishing nearly impossible in some places, as they clogged gear, stole bait or ate trapped fish.