Ecology of the fishes of the Norwegian Deep: Distribution and species assemblages

Abstract

An account based on hydroacoustic data and trawl surveys of the distributional patterns and species assemblages of the fishes inhabiting the Norwegian Deep and adjacent slopes is presented. The Norwegian Deep is the moderately deep (275 to 700 m) shelf channel extending from the Norwegian Sea into the North Sea and Skagerrak. The Norwegian Deep has a pelagic and demersal fish fauna which is rather different from the fauna in adjacent shallow areas. Blue whiting ( Micromesistius poutassou) and Maurolicu muelleri form a widely distributed and normally two-layered pelagic association. There appears to exist a rather sharp boundary at about the 200 m isobath between species assemblages of the Norwegian Deep and those of the shallow plateaus of the North Sea and Skagerrak. The fish fauna of deeper zones of the Skagerrak differs from the areas off western and southwestern Norway. The more conspicuous feature in the Skagerrak is the rather high abundance of greater argentine ( Argentina silus) and roundnose grenadier ( Coryphaenoides rupestris) at depths greater than 300 m. The species assemblages of the Norwegian Deep resemble those found in the areas along the outer shelf of the Northeast Atlantic and the deep fjords of Norway. The western and southern slopes appear to be feeding and overwintering areas for some fish species from adjacent shallow areas, particularly populations of saithe ( Pollachius virens) and Norway pout ( Trisopterus esmarki). It is suggested that the Norwegian Deep, due to its characteristic bathymetry and the strong influence of Atlantic inflow, is colonized by mesopelagic and benthic species from the other shelf areas of the Northeast Atlantic. The shelf channel appears to be deep enough to allow outer shelf species temporary or permanent access to the inner shelf environment.