Fish communities on the slop of the eastern Norwegian Sea

Abstract

Bortom trawl data from the depth interval 300-2050 m on the slope off Norway were analysed to study distribution of fish biomass and the associated species assemblages. It is hypothesised that the pronounced hydrographic front between the warm Atlantic Waterrnass and the cold Norwegian Sea Deep-water, combined with a declining food supply with depth and distance from the shelf, structure the assemblages on the continental slope of the eastem Nmwegian Sea. From a high level at the shelf edge and upper slope, the fish biomass declined abruptly at about 720 m when crossing the 0"C-isotherm associated with the hydrographic front. Beneath the frontal zone, the fish biornass was only 11% of that above it and decreased further with increasing depth. In upper slope waters, the fish biornass increased with increasing latitude. Arctic species such as Lycodes frigidus and Paraliparis bathybius were dominant in the deep cold slope waters. The high fish biomass associated with the steep temperature gradient at 600-720 m was rnainly attributable to a few large and/or abundant boreo-arctic species, i.e. Greenland halibut Reinhardtius hippoglossoides, redfishes Sebastes mentella and S. marinus, roughhead grenadier Macrourus berglax, and Raja hyperborea. In the shallower and warrner upper slope waters a species assemblage occurred which resembled that associated with adjacent deep shelf areas strongly influenced by the Atlantic Watermass.