Food and feeding conditions of Norwegian spring-spawning herring (Clupea harengus) through its feeding migrations

The feeding ecology of herring was studied using samples collected during cruises in 1994, 1995, and 1996 in the More shelf region off western Norway, where the major spawning of herring occurs, and in the off-shelf area of the eastern and central Norwegian Sea, where herring migrate after spawning. After spawning in February and March, herring fed upon euphausiids, mainly Thysanoessa inermis and Meganyctiphanes norvegica on the shelf and at the shelf edge. In late spring and summer, herring that had migrated to the Norwegian Sea fed primarily on Calanus finmarchicus, copepodid stage IV and older. In colder waters e.g., those influenced by the East Icelandic Current, C, hyperboreus was important in the diet. By July and August, a wide variety of prey organisms was found in the stomachs of herring caught in the central Norwegian Sea and on the Norwegian continental shelf. In the western part of the Norwegian Sea, amphipods, Themisto spp., were important prey. The herring showed size-selective feeding on copepodid stages of C. finmarchicus and C. hyperboreus. Larger prey, such as krill and amphipods, were preyed upon regardless of their size. The average weight of food in the stomach was generally higher in the mixed Atlantic/Arctic and Arctic waters, which were also characterized by higher zooplankton biomass. (C) 2000 International Council for the Exploration of the Sea.