DEMERSAL ICHTHYOFAUNAL DISTRIBUTION IN THE ABYSSAL EASTERN NORTH-ATLANTIC, WITH SPECIAL REFERENCE TO CORYPHAENOIDES-(NEMATONURUS)-ARMATUS (MACROURIDAE)

Three latitudinally separated assemblages (49-degrees-41-degrees-N,38-degrees-30-degrees-N,22-degrees-20-degrees-N in 11-degrees-25-degrees-W) of abyssal demersal fishes in the eastern North Atlantic have been identified from combined data from 13 new and 12 previously reported trawl samples. The northerly assemblage remained unaltered by the new data, but the intermediate one could be sub-divided into shallow (4370-4475 m) and deep (4835-5440 m) elements. This sub-division revealed that bathymetry was acting with latitude to influence previous results. The new, southerly, assemblage was found below surface waters enriched by upwelling along the continental margin. The composition of dominant species identified each assemblage. The biological characteristics of these species were largely consistent with the former hypothesis linking them to the influence of the overlying production regime. The contrast between this preliminary evidence for structured demersal fish assemblages in the abyss with its lack on the slope and rise was discussed in the terms of the respective patterns of trophic input. Evaluation of the population biology of 1205 Coryphaenoides (Nematonurus) armatus indicated substantial peaks in relative biomass and abundance only in the northerly assemblage, to substantiate this grouping further. Bathymetric distribution of these parameters indicated a 'smaller-shallower' trend, which was confirmed from geometric mean sizes per sample. Sexual dimorphism in size and bathymetric variation in sex ratio indicated that the smaller, male, sex occurred mainly in the upper part of the sounding range. This apparently complex bathymetric structure emphasized the importance of sampling strategy in the investigation of population biology in such species.