Habitat use by juvenile Dungeness crabs in coastal nursery estuaries

Juvenile Dungeness crabs are found extensively throughout U.S. West Coast estuaries. Trawl surveys targeting juvenile Dungeness crabs were conducted in the summers of 1998-2000 in four West Coast estuaries: Coos Bay and Yaquina Bay, Oregon, and Grays Harbor and Willapa Bay, Washington. Additional data from surveys in Willapa Bay (1985-1988) and Grays Harbor (1983-1988) were also utilized in this study. Densities of age 0+ and age 1+ juvenile crabs were analyzed using analysis of variance techniques for each of the four estuaries. Patterns of crab density in each of the four estuarine systems suggest they prefer lower side channel sites close to the estuary mouth. Our trawl survey data indicate that crabs utilize these subregions of estuaries which are characterized by broad intertidal flats with extensive secondary subtidal channels. These subregions are further characterized by abundant local refuge (shell, macroalgae), high prey abundance, shallow depths, temperatures less than 18degreesC, and relatively high salinities. Significant interannual variation was evident for both age classes. Mean density for age 0+ crabs varied by a factor of 54 over the years studied, while mean density varied only by a factor of 7 for age 1+ crabs.