Distribution of bottom-trawl fish assemblages over the continental shelf and upper slope of the US west coast, 1977-1992

Twenty-three bottom-trawl fish assemblages were identified from the relative biomass of 33 dominant species that occurred in the National Marine Fisheries Service's triennial trawl surveys over the continental shelf and upper slope off California, Oregon, and Washington from 1977 to 1992. The assemblages accounted for about 70% of the total variation in species composition among 2565 hauls. Although the assemblages persisted over the 15-year study period and occurred within broad geographic boundaries, some had substantially different spatial distributions among surveys. The ability to differentiate assemblages across five environmental variables (latitude, depth, surface and bottom water temperatures, and surficial substrate) was low. The preponderance of bake-dominated assemblages throughout the study area suggests that Pacific bake (Merluccius productus) may play a large role in the dynamics of demersal fish communities off the west coast of the United States.