Trophic diversity in deep-sea fish

The general composition and diversity of the diets of the 43 most commonly caught pelagic and demersal fish of the Rockall Trough, north-eastern Atlantic Ocean, are assessed. The fish are divided into three Groups. The 8 species in Group I consist of both pelagic and demersal species feeding on relatively few prey-classes and having a diet of low diversity and few items per meal. Group II contains 22 pelagic and demersal species with more diverse diets, less restricted dietary composition, but still consuming relatively few items per meal. Group III is the 12 demersal macrourid species with the most diverse diets, a variable dietary composition and the greatest mean number of items per meal. One species, Maurolicus muelleri , had too many unidentified components in its diet to allow classification in terms of Groups I, II or III. All diets contained dominant items, the diversity within diets offish in Groups II and III arising from the inclusion of subdominants and rare items. The diets of species in Groups I and II can be defined in terms of ecological constitution, trophic diversity and prey-species composition. Those of the Group III macrourids differ in that their definition is liable to be a compromise between the situation where ecological constitution and trophic diversity are adequately defined but not species composition.