California Department of Fish and Wildlife

Bay Delta Region

Main Office
  7329 Silverado Trail
  Napa, CA 94558
  (707) 944-5500

Stockton Office
  2109 Arch Airport Rd
  Stockton, CA 95206
  (209) 234-3420

Regional Manager:
Scott Wilson

What's New on the Mitten Crab Front?

Tanya Veldhuizen, DWR, and Kathy Hieb, DFG

The Chinese mitten crab, Eriocheir sinesis, has rapidly increased its distribution in the San Francisco Estuary and watershed since it was first discovered in south San Francisco Bay in 1992. As of July 1998, the known distribution of the Chinese mitten crab extends north to Hunter's Creek(near Delevan National Wildlife Area) in the Sacramento River drainage and near Nicolaus in the Feather River, east to Roseville(Cirby Creek) and eastern San Joaquin County (Escalon-Bellota Weir on the Calaveras River and Littlejohns Creek near Farmington)and south to the San Luis National Wildlife Refuge near Gustine. We also have an unconfirmed report from the lower Stanislaus River. The mittencrab's distribution is also expanding in tributaries to San Pablo Bay, with sightings from all the major tributaries to Petaluma Creek and from a tributary to Sonoma Creek near Sonoma. It has been found throughout the Delta and South Bay tributaries.

Any crab found in fresh water is likely to be a mitten crab. The main identifying characteristic of the mitten crab is brown "hair" on the frontclaws. Very small juveniles (< 25 mm carapace width)rarely have "hairy" claws and may be confused with another non-native crab, the Harris mud crab (Rithropanopeus harrisi).The Harris mud crab is occasionally found in fresh water and can be distinguishedfrom small mitten crabs by the ridges on its carapace and lack of a notchbetween its eyes. Please refer to the chart below for more specifics onthe identifying characteristics.

If you find a mitten crab beyond the current known range, please notify Kathy Hieb with the collection information (i.e. date, location, size,number, collection method, and contact person). You do not need to send us the crab.

Remember, it is illegal to import, transport, or possess live Chinese mitten crabs (Title 14 of the California Code of Regulations). Accidental release or escape will spread these crabs to uninfested waters. If you keep a mitten crab, it must be dead.