Vertical distribution of herring larvae in relation to physical mixing and illumination

Vertical distributions of 3 size groups of herring larvae Clupea harengus L. in isothermal and stratified waters off the north coast of Scotland were recorded by repetitive sampling, adjacent to dnfting markers, with an opening and closing high-speed plankton net. Concurrent measurements of light intensity at the sea surface, wind velocity and water column hydrography were related to the distributions of larvae by time series analysis. Results indicate that larvae in the size range 6 to 18 mm aggregated to form a layered distribution during the day but dispersed at night. However, the mean depth of the populahon was most strongly influenced by turbulence, especially wind-induced mixing. A predlchve model of larval vertical distribution has been derived.