A series of night hauls were made both along a transect from the Danish coast to the Dogger Bank and at a fixed position in the southern North Sea. The aim was to evaluate the suitability of two midwater trawls (IKMT and MIK) for catching large herring larvae (20-40 mm), with special attention given to the influence of gear speed on catching effectiveness. An additional objective was to investigate larval distributional patterns of potential importance to sampling strategy. Gear speed had a pronounced influence on the efficiency of the IKMT. Catches per unit volume filtered decreased to one third when speed was increased by one knot. The efficiency of the MIK did not change in the speed range investigated, and this gear was in every case more efficient than the IKMT. Larvae were found to be patchily distributed at the scale of sampling, and the degree of patchiness did not increase when stations 5 nm apart were compared. At night, herring larvae are confined to the 20-40-metre water layer, whereas a migration to upper water layers at dawn and dusk was observed.
|Journal||Journal de Conseil - Conseil International pour l'Exploration de la Mer|
|Publication status||Published - 1988|