The food of Norwegian spring-spawning herring in the western Norwegian Sea in relation to the annual cycle of zooplankton

Abstract

No abstracts are to be cited without prior reference to the author.The food of the Norwegian spring spawning herring (Clupea harengus) in the western part of the Norwegian Sea was studied. The material was collected on 3 cruises in 1995 (April, May, June) and 2 cruises in 1996 (May, June). A total of 653 stomachs of herring, ranging in length from 24.1 to 44.0 cm, were examined. Of these 622 or 95% were found to contain food. The feeding activity of the herring was higher in May and June than in April, as indicated by both the higher proportion of stomachs with food in May and June (>95%) than in April (~82%), and the higher average stomach content in May and June (~830 and ~760 mg dry weight, respectively) than in April (~40 mg dry weight). Copepods (mainly Calanus finmarchicus, C. hyperboreus and Metridia longa) were the most important prey of herring, both in terms of numbers (~25->98%) and biomass (~50-90%). In June, amphipods (mainly Themisto abyssorum) were also important in the diet both in numbers (~10-50%) and biomass (~10-30%). Euphausiids (mainly Meganyctiphanes norvegica) were most important as prey of herring in June (~0-25% and ~0-10% by numbers and dry weight, respectively). The relations between herring migrations and the seasonal development of zooplankton are discussed.