Distribution, migration and abundance of norwegian spring spawning herring in relation to the temperature and zooplankton biomass in the Norwegian sea as recorded by coordinated surveys in spring and summer 1996

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Abstract
The distribution and migration of Norwegian spring spawning herring (Clupea harengus) in the Norwegian Sea in spring and summer 1996 were mapped during 13 coordinated surveys carried out by Faroese, Icelandic, Norwegian and Russian research vessels. After spawning at the banks of the Norwegian Coast in February-March, most ofthe spent herring migrated out in the Norwegian Sea through a corridor between 67°N and 68°N. In May, 4 and 5 year old herring, which form the younger part of the spawning stock, were distributed in small schools or scattered layers at 25-100 m depth over large areas of the central Norwegian Sea. Older and larger herring formed large schools, generally at 250-400 m depth near the cold front along the eastern part ofthe Icelandic Exclusive Economic Zone (EEZ). The total abundance of herring in the Norwegian Sea was estimated to be about 47 billion individuals or about 8 million tonnes. In June, the older and larger herring had migrated northwards into the Jan Mayen zone, while the younger herring remained in the southern and central Norwegian Sea. In July, the younger herring had migrated back to the area offVesterMen, northern Norway. In July/August, the larger herring were found in small schools near the surface in the northern Norwegian Sea. Relationships between the temperature distribution, zooplankton abundance and herring distribution and migration are considered. In May, the lowest zooplankton biomass was observed in the central and southern Norwegian Sea. At that time, there were high zooplankton concentrations in the westernmost part of the Norwegian Sea, within the domain of the East Icelandic Current. The herring did not enter this body of cold water with temperatures of 1–2°C in the uppermost 300 m, but migrated to the north and north-east in search of food.