Mediterranean and Atlantic deep-sea fish assemblages: differences in biomass composition and size-related structure

Data obtained over a period of twenty years from 214 bottom trawls, towed on a single warp at depths between 402 and 1993 m in the western Mediterranean (Algerian and Balearic basins) and eastern North Atlantic (Rockall Trough and Porcupine Seabight), allowed a standardised comparison of density, biomass composition and size-related structure for both the whole fish fauna and for the most common species found within the deep-sea fish assemblages. All four areas are characterised by distinctly different and well-documented oceanographic conditions, biogeographical affinities and fishing exploitation. The results showed clear differences between the Atlantic and the Mediterranean deep-sea fish fauna, not only in density, species richness and composition, but also in the structure of the biomass that constitutes these assemblages. These differences are discussed in relation to environmental conditions and fishing pattern, which have determined the adaptive responses of both individual species and the whole ecosystem.