Five Questions About the Chinese Mitten Crab:
1) How is the Chinese Mitten Crab (Eriocheir sinensis) different from other species, like the blue crab?
Blue crabs swim, mitten crabs walk. They have incredibly long legs that can be twice the length of the carapace's width. Mitten crabs can also survive for days outside of the water; for an aquatic crab this is unusual. For large (especially adult) mitten crabs, one of the most unique physical characteristics is the furry or hairy appearance of their claws. Thick patches of setae, or bristles, cover their claws -- earning them their common name, "mitten crab."
2) The Chinese mitten crab is native to Korea and Northern China, where is it found today?
There are established populations throughout Europe that were detected in the early 20th century. The first report of a mitten crab in North America occurred in 1965, when one was caught in a water intake pipe in the Great Lakes. Even though additional crabs have been recorded in the Great Lakes region, this does not appear to be a self-sustaining population. The first established (self-sustaining) US population was in San Francisco Bay, California. It appears that the Chinese Mitten Crab has now also established a population in the mid-Atlantic region, where over 100 crabs have been recorded, including reproductive (egg-bearing) females.
3) Where would you expect to find one in the wild?
Chinese mitten crabs can be difficult to find, even when present. The commonly occur in shallow waters (<20 feet depth) in bays and estuaries, as well as upstream in rivers and streams. When in freshwater, the crabs spend much of their time burrowed in riverbanks and under rocks. They are catadromous, which means they live most of their lives in freshwater and then migrate to salt water to spawn. They've been known to move more than 800 miles inland from marine and estuarine waters. If you live near a tributary that feeds into the New Jersey intercostals or the Chesapeake, Delaware, or Raritan Bays, be on the lookout. Also, commercial fishermen have found Chinese Mitten Crabs in their traps and nets, especially in spring and early summer.
4) So what if the Chinese Mitten Crab gets established on the East Coast?
In Europe and California, the introduction of mitten crabs has had both ecological and economic effects in aquatic habitats. It's possible that similar effects would occur on the US Atlantic Coast, especially in years when the crab is abundant (if this occurs).
5) What type of economic damage could a crab with furry claws cause?
When these crabs migrate from freshwater to saltwater, they can move in large numbers. In California and Germany, their mass migrations have destroyed the nets and lines of shrimpers and other fishermen. The mitten crabs have also been known to steal bait intended for other fish. And during certain parts of their lifecycle, they may compete for food or habitat with native species, like the blue crab, and may also be an important predator during periods of high abundance.
Mitten crabs can also harm infrastructure. They have clogged water intake pipes at power plants in California and Europe and can damage levees and dikes by burrowing and increasing erosion.