DEEP DEMERSAL FISH ASSEMBLAGE STRUCTURE IN THE PORCUPINE SEABIGHT (EASTERN NORTH-ATLANTIC) - RESULTS OF SINGLE WARP TRAWLING AT LOWER SLOPE TO ABYSSAL SOUNDINGS

Thirty-four tows of an 8.6-m wing-end spread semi-balloon trawl made between 2230 and 4787 m in the Porcupine Seabight and Abyssal Plain (eastern North Atlantic) were used to investigate demersal ichthyofaunal ecology. The catches yielded almost 300 specimens, representing 15 families and 43 species. In species richness the families were dominated by the Alepocephalidae and Macrouridae, in abundance by the Macrouridae and Moridae. Restricted sounding ranges of varying width produced different trends in species first and last occurrence with increased soundings. Evidence of improved sampling efficiency below 2200 m sounding suggested that relative abundance and biomass estimates of this trawl are more reliable than at shallower soundings. Tentative comparisons in abundance and biomass with samples from other regions indicated that the Porcupine area yielded similar or slightly lower values. The so-called 'bigger-deeper' trend (Heincke's Law) was examined from upper slope to abyss. It was shown to be a sampling artefact arising from avoidance of small trawls by large specimens at mid- and upper-slope soundings. At specific level, however, a 'smaller-shallower' trend was confirmed among several species.