Community Structure of Small Demersal Fishes along the Oregon Coast

Small demersal fishes were collected along the Central Oregon coast using a shrimp trawl with small-mesh liner, which was deployed bimonthly in 1989 along three transects and along a single transect in March of 1989-1994.  Forty-three species, 19 of which are not commercially important and rarely reported in other studies, occurred in >5% of the samples.  Species assemblages were structured primarily by depth, with mid-shelf stations dominated by flatfishes, while gadids, scorpaenids, osmerids, and zoarcids were also important on the outer shelf and slope.  Additionally, four of five identified station groups were most closely associated with a single season. Seasonal assemblage structure included a broad range of species whose distributions shifted inshore in summer. This phenomenon, only previously described for a few species off Oregon, further accentuated the correlation of assemblages with depth. It appeared to be a function of juvenile settlement and ontogenetic changes in nursery habitat, of seasonal inshore-offshore movements of individuals of many sizes, and indicated that sediment type was not the only feature important in habitat selection. March assemblages were weakly structured by interannual differences, in spite of environmental conditions ranging from the cold La Niña of 1989 to the warm El Niño of 1992.  The largest annual differences were among short-lived species that likely reflected differences in recruitment. This work, targeting smaller fish than are collected in most bottom trawl surveys, illustrates the importance of seasonal changes in habitat for smaller fish and the value of understanding all life stages in a demersal fish community.