Seasonal and interannual variability in the community structure of small demersal fishes off the central oregon coast

Abstract

5% of the samples. Species assemblages were structured primarily by depth, with mid-shelf stations dominated by flatfishes; on the outer shelf and slope, gadids, scorpaenids, osmerids, and zoarcids were also important. Additionally, 4 out of 5 identified station groups were more closely associated with a single season. Seasonal assemblage structure included a broad range of species whose distributions shifted inshore in summer. This phenomenon, previously described for only a few species off Oregon, further accentuated the correlation of assemblages with depth. Seasonal shifts in distributions appeared to be a function of juvenile settlement and ontogenetic changes in nursery habitat and of seasonal inshore-offshore movements of individuals of many sizes, which 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 Nin∼a of 1989 to the warm El Nin∼o of 1992. The largest annual differences were among short-lived species and likely reflected differences in recruitment. This study targeted smaller fish than are collected in most bottom trawl surveys and illustrates the importance of seasonal changes in habitat for smaller fish and the value of understanding all life stages in a demersal fish community. © Inter-Research 2011.