San Francisco Bay Invasion

In the 1970's an invertebrate systematist at the California Academy of Science (CAS) in San Francisco noticed that live mitten crabs were available for importation into the United States (Cohen and Carlton 1995). A highly valued delicacy (worth upwards of $30/kg), live mitten crabs were found for sale in seafood markets in Los Angeles and San Francisco in the 1980's by the California Department of Fish and Game (Cohen and Carlton 1997). Concern over the potential damage their burrows could cause as well as fears of a human health hazard from the parasite Paragonimus westermanii (an oriental lung fluke that causes sometimes-fatal, tuberculosis-like symptoms) for which the mitten crab is a secondary host, led to a ban of mitten crabs in California in 1987. In 1989 the United States (US) listed the Chinese mitten crab as an "injurious species" (50 CFR 16.13) making its importation, capture and possession a serious crime.

Despite this ban on the import of mitten crabs into the US, they have become successfully established in San Francisco Bay (Carlton and Cohen 1997, Halat and Resh 1996). In 1994 a shrimp fisherman in South San Francisco Bay caught an unfamiliar crab in his nets and brought it to CAS for identification (Cohen and Carlton 1995). That was the first recorded mitten crab in San Francisco Bay, although shrimp trawlers later reported having occasionally caught mitten crabs as far back as 1992. Cohen and Carlton (1997) conclude that ballast water is the most probable vector responsible for introducing the crabs. They also suggest that an intentional planting of mitten crabs to establish a food resource may have occured.

created 5/4/98