Migration behaviour of Norwegian spring spawning herring when entering the cold front in the Norwegian Sea
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The distribution of Norwegian spring spawning herring when migrating to the feeding areas in the Norwegian Sea in spring has been mapped by surveys in April1995 and 1996. The schooling behaviour of the herring have been recorded by a high resolution sonar, and the swimming speed and swimming direction have been quantified by tracking individual schools for up to one hour. In early April the herring is migrating westwards in the Norwegian Sea between 66° north to 68° north and the continental shelf off Norway and westwards to 0°. When reaching the cold front at about 0° the herring turn southwards along the front. The herring is migrating in large schools or extended layers at 300- 400 m depth in daytime. At night the herring rise to surface, and disperce or maintain schooling.