Spatial patterns of groundfish assemblages on the continental shelf of Portugal

The analysis of catch data from groundfish surveys (1985-1988) conducted on the Portuguese shelf and upper slope (20-500 m) revealed five major geogra phic areas, each characterized by the presence of a typical fish assemblage . These areas of distinct fish assemblages were found to be closely aligned with depth, in a way that resembles spatial patterns previously described for other continental shelves in the North Atlantic. The sharpest biologica l transition on the Portuguese shelf takes place as one moves from areas sh allower than 120 m ("Shallow Groups") towards deeper locations offshore ("D eep Groups"). Beyond the 150 m isobath, the biomass was dominated by blue w hiting, whereas inshore variability in assemblage composition was much grea ter. Species such as sardine, horse mackerel. mackerel(to the north of Lisb on) and sparids (io the south) comprised significant and highly variable pr oportions of the population abundance inshore. There are similarities betwe en the trophic and spatial organization of the marine community on the Port uguese shelf and that of other coastal upwelling ecosystems that are briefl y reviewed here. (C) 2001 International Council for the Exploration of the Sea.