ASSEMBLAGES AND BIOGEOGRAPHY OF DEMERSAL FISHES OF THE EAST-COAST OF NORTH-AMERICA

This study describes and maps demersal fish assemblages for the east c oast of North America from Cape Hatteras, North Carolina, to Cape Chid ley: Labrador, evaluates evidence for interannual shifts in assemblage distribution, and examines the relationship of the assemblages to acc epted biogeographical boundaries. Demersal trawl survey data collected from 1975 to 1994 were analyzed. Visual classification of distributio n maps for the 108 most abundant demersal species revealed nine specie s groups, based on both geography and depth distribution. Eighteen ass emblage groups were identified using principal components analysis (PC A) and mapped. Assemblage groups were also identified by cluster analy sis. Fish assemblages identified by both methods were spatially cohere nt. Assemblage distribution patterns were not consistent with accepted biogeographical boundaries. The PCA explained only 56.3% of the varia nce in distribution of the species, indicating that the assemblages sh ould be interpreted as indeterminate, potentially adaptable entities r ather than as rigid ecological constructs. Assemblages were persistent in composition through time but appeared to shift, in location. The a pparent looseness of the assemblages and their persistence through tim e in spite of severe impacts from fishing suggest that single-species management approaches may not be entirely inappropriate for the major groundfish species in the study area.