Spatial and temporal stability of commercial groundfish assemblages off Oregon and Washington as inferred from Oregon trawl logbooks

Abstract

Spatial and temporal characteristics of species compositions for 15 major commercial groundfish species off Oregon and Washington (U.S.A.) were studied using Oregon bottom trawl logbook data from 1987 to 1993. Screening procedures to remove questionable data from the original logbook files resulted in the exclusion of information from 46% of the total available tows. Two multivariate methods, detrended correspondence analysis and Ward's hierarchical cluster analysis, were used to derive species ordinations and groupings. A general linear model developed for the primary detrended correspondence analysis axis scores showed that the species compositions were strongly correlated with depth and minimally correlated with the other environmental variables examined (latitude, month, and year). However, there were distinct seasonal changes in species composition at the shallower depths, consistent with the movement of deepwater species onto the shelf during summer. Annual trends in the species compositions were not evident even though the study region is very dynamic oceanographically and was heavily fished during the study period.