Feeding and migration of Norwegian spring spawning herring in the Norwegian Sea

After spawning on the shelf off Møre, Western Norway, the spawning stock of\nNorwegian spring spawning herring migrates to the Norwegian Sea for feeding.\nSimultaneously, the adolescent part of the stock leaves the wintering areas in\nfjords and coastal areas of northern Norway and starts feeding in the Norwegian\nSea. During two cruises in April and June 1994, a transect from coastal water over\nthe Norwegian continental shelf across the frontal zone into Atlantic water in the\ncentral Norwegian Sea was covered. Distribution and development of major prey\nspecies of the herring, Calanus finmarchicus and C. hyperboreus, were described\nin relation to hydrography and phytoplankton spring bloom dynamics.\nIn April, all year-classes of herring were found in Atlantic water where\nzooplankton biomass was high in the upper 50 m of the water column. C.\nfinmarchicus occurred in the overwintering stages CV and adult females, and\nfeeding conditions were probably good. The older year-classes of herring showed a\nwesterly movement along the transect from April to June, and the oldest herring\nwere found farthest to the west. The herring did not cross the Polar front into\nArctic water masses in June, although feeding conditions, judged from\nzooplankton biomass distributions, seemed far better than in Atlantic water. The\nherring in June was distributed in Atlantic water masses with low biomass of\nsmall stages of the new generation of C. finmarchicus, and feeding conditions\nwere probably not optimal.\nThe young year-classes of herring, which were found in Atlantic water in April,\noccurred over the shelf in June. There the zooplankton biomass was\nintermediate, but the new generation of C. finmarchicus had developed into late\ncopepodite stages and adults and served as potential large particle food items for\nthe herring.