Spatial patterns of groundfish assemblages on the continental shelf of Portugal

Abstract

The analysis of catch data from groundfish surveys (1985-1988) conducted on the Portuguese shelf and upper slope (20-500 m) revealed five major geographic 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 biological transition on the Portuguese shelf takes place as one moves from areas shallower than 120 m ("Shallow Groups") towards deeper locations offshore ("Deep Groups"). Beyond the 150 m isobath, the biomass was dominated by blue whiting, whereas inshore variability in assemblage composition was much greater. Species such as sardine, horse mackerel, mackerel (to the north of Lisbon) and sparids (to the south) comprised significant and highly variable proportions of the population abundance inshore. There are similarities between the trophic and spatial organization of the marine community on the Portuguese shelf and that of other coastal upwelling ecosystems that are briefly reviewed here. © 2001 International Council for the Exploration of the Sea.