Fisheries & Aquaculture

Deep Water and Demersal Fisheries

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The deep-water demersal fishes are generally divided into two categories, benthic and bentho-pelagic. The benthic fishes are those that have a close association with the seabed and include species such as skates and flatfishes. Bentho-pelagic fishes are those that swim freely and habitually near the ocean floor and, in the areas where deep-water fisheries are commercially viable, they comprise most of the exploited biomass. The general concept of the deep sea is of a dark, cold, food scarce environment where biomass decreases exponentially with depth. How then do the continental slopes, underwater rises and seamounts in some areas of the world support deep-water fisheries? The demersal fish populations of the slopes of the Rockall Trough have been the subject of intensive study by the Scottish Association for Marine Science (SAMS) since the mid1970s and these studies have contributed to an explanation of this phenomenon. By using fine mesh bottom trawls capable of catching almost all sizes of fish it has been shown that there is a diverse demersal fish fauna of in excess of 130 species between about 400 metres and abyssal depths.