Deep Demersal Fish Assemblage Structure in the Porcupine Seabight (Eastern North Atlantic): Results of Single Warp Trawling at Lower Slope to Abyssal Soundings

Abstract

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 3800 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 soundings 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.

Small-scale distribution of deep-sea demersal nekton and other megafauna in the Charlie-Gibbs Fracture Zone of the Mid-Atlantic Ridge

“…Distributions of nekton and also of large holothurians were less easy to characterize. The blue hake A. rostrata and alepocephalids were seen only in the shallower parts of the ridge covered by MIR 1, coinciding with their known depth ranges (Merrett et al, 1991). Shrimp and the squat lobster Munidopsis sp.…”

“…Large macrourids were the next most common forms, and represented more than a single species. Those seen clearly enough to identify included the abyssal grenadier Coryphaenoides (Nematonurus) armatus and probably the ghostly grenadier Coryphaenoides (Chalinura) leptolepis (the most abundantly caught macrourid of the subgenus Chalinura in the eastern Atlantic, Merrett et al, 1991). Both small and large macrourids were usually seen hovering over the bottom, and sometimes in contact with the bottom.…”

Trends in body size across an environmental gradient: A differential response in scavenging and non-scavenging demersal deep-sea fish

“…Early studies of the demersal deep-sea ichthyofauna indicated a general pattern of increased size with depth (Polloni et al 1979), which came to be known as Heincke's Law (following Heincke's (1913) description of the size of plaice in the North Sea). However, subsequent work demonstrated that the phenomenon was not ubiquitous (Snelgrove & Haedrich 1985), may be an artefact of sampling (Merrett et al 1991b) and in some regions a decline in size with depth has been reported (Stefanescu et al 1992).…”

Depth-size trends in western Mediterranean demersal deep-sea fishes

“…However subsequent studies have proved that this tendency changes according to the area C 3 Inter-Research/Printed in Germany studied (Merrett & Marshal1 1981, Sulak 1982, Snelgrove & Haedrich 1985, Gordon 1986, Merrett 1987. The confusion has led some authors to suggest that the bigger-deeper phenomenon could be nothing more than a sampling artefact (Pearcy et al 1982); in one area, at least, evidence has shown this to b e so (Merrett et al 1991b).…”

“…Within-species the observed trend is also variable (Polloni et al 1979, Mauchline & Cordon 1984, Snelgrove & Haedrich 1985, Middleton & Musick 1986, Gordon & Duncan 1987, Macpherson & Duarte 1991, Merrett et al 1991b. In some taxonomic groups (e.g, gadiforms) the occurrence of larger individuals in deeper waters is a fairly common pattern.…”