Demersal fish on the continental slope off Norway

Abstract

Investigations on distribution and abundance of demersal fish in 400-1000 m depth were carried out in three selected areas off Norway in July-August 1974. Based on catches in 48 hauls by bottom trawl and 3 long-line settings the relationships between depth, fish quantity and species composition were determined. In 800 m the catch in weight was reduced to about 10% and in 1000 m to 1 % of that taken on the edge of the shelf (400-500 m). The number of fish species caught was reduced from about 10 to 3 over the same depth range as boreal species were replaced by a few arctic species. Trawl catches were small, about 70 kg per hr in 600 m, while long-line in this depth gave 150 kg per 1000 hooks; mostly Macrourus berglax, Raja hyperborea and Reinhardtius hippoglossoides. The abundance and vertical distribution of the fish on the continental slope are closely related to the hydrography of the Norwegian Sea. Atlantic water with temperature 5-7º C cover the edge of the shelf down to a bout 500 m while deep water of arctic origin with typical temperature -0.9º C is found along the slope in depths below 600-700 m. A variable transitional layer occurs between. Prospects of commercial utilization of the fish resources on the slope are briefly discussed.