Distribution of the non-indigenous European green crab, Carcinus maenas,

in Humboldt Bay, 1998-2001

The European green crab, Carcinus maenas, was first detected on the West Coast in San Francisco Bay in the late 1980's. In Humboldt Bay, green crabs were first detected in 1995. Trapping studies in 1996-97 caught few (9) crabs but in 1998 large numbers were found in the intertidal areas of Humboldt Bay. Their habitat and feeding preferences overlap with many species found in Humboldt Bay, primarily those of the Dungeness crab. Documented destruction of shellfish resources on the Eastern Atlantic Coast by green crabs caused concern among local resource managers and fishermen, that green crabs may impact juvenile Dungeness crabs that settle by the thousands in Humboldt Bay and may prey upon juvenile cultured oysters, clams and mussels. The objective of this study was to determine the distribution of green crabs in Humboldt Bay. Intertidal and subtidal baited traps were deployed for 24 hours at 30 sites around Humboldt Bay each year. The number of green crabs trapped decreased between 1998 and 2000 but increased in 2001. Green crabs were found throughout Humboldt Bay in 1998 and 1999 but by 2000 and 2001, two populations, Mad River Slough and the southwest corner of South Bay, appear to be established. Both population centers are located in marshy, protected sites. No green crabs were found in subtidal traps, possibly as a result of large populations and large individuals of native Cancer spp. crabs.