Migration behaviour of norwegian spring spawning herring when entering the cold front in the Norwegian Sea

The distribution of Norwegian spring spawning herring when migrating to the feeding areas in the Norwegian Sea in spring was mapped by acoustic surveys in April 1995 and 1996. The schooling behaviour of the herring was recorded by a high-resolution sonar, and the swimming speed and swimming direction were quantified by tracking individual schools for up to one hour. In early April the herring migrated in the Norwegian Sea from the continental shelf off Norway, between 66° and 68°N, and westward to 2°W. When reaching the cold-water front, at about 0°, the herring turned southward along the front. During daytime the herring migrated in large schools at 300–400 m depth; at night they rose to surface and either dispersed or maintained schooling.