DISTRIBUTION AND TROPHIC ECOLOGY OF SOME GADOID FISH OF THE NORWEGIAN DEEP .2. FOOD-WEB LINKAGES AND COMPARISONS OF DIETS AND DISTRIBUTIONS

The paper concerns the ecology of selected species of the suborder Gadoidei (Pisces, Gadiformes) inhabiting the deeper parts of the northeastern North Sea and Skagerrak. In this final part of the paper, interspecific relationships and comparisons are emphasised. The nine large gadoids considered are primarily benthopelagic and pelagic predators on fish and crustaceans. Because of their abundance and wide distribution, they are key members of the upper part of the food-web in the Norwegian Deep and its slopes. Particularly important trophic relationships exist between the gadoids and the euphausids, caridean decapods and Norway pout. It is likely that the strongest interactions involving the gadoids are of predator-prey type and exist between the most abundant gadoids and their main prey: small saithe and blue whiting as predators and the euphausids as prey, and between saithe and Norway pout. Because it seems unlikely that any of the species, even those showing rather extensive overlaps in their diets and spatial distributions, experience resource shortages, the overall impression is that competition plays a minor role among the gadoids. However, intraspecific resource overlap seemed rather strong among the lifestages found in this area. Therefore, significant influence of competitive interactions are more likely to be found between size groups of the same species than between different species.