Influence of sea temperature on herring distribution and migration in the Norwegian Sea in April 1997
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After spawning at the west coast of Norway, the Norwegian spring spawning herring migrates northwestwards into the Norwegian Sea to feed in early April. The herring enters areas with distinct oceanographic features both horizontally and vertically in the frontal zone between the warrn Atlantic water and the cold Arctic water. The Atlantic water enters the central Norwegian Sea by means of the outer branch of the Norwegian Atlantic current which runs northeastwards and further north- and northwestwards from the Faroe Islands as an unstable frontal jet. To investigate the influence of sea temperature on the distribution and migration of herring, we performed two synoptic transects with the research vessels R/V "G.O. Sars" and R/V "Håkon Mosby" in April 1997. The R/V ''G.O. Sars" recorded the herring distribution by echo integration, tracked selected schools by sonar and took samples by pelagic trawl, while R/V "Håkon Mosby" canied out continuous sea temperature and salinity recordings of the transects by operating a SeaSoar vehicle, undulating from sea surface to 300 m depth. The relations between sea temperature, herring distribution and migrations horizontally and vertically are studied by combining the synoptic recordings from the two research vessels.