Growth and advection of larval herring ( Clupea harengus L.) in the vicinity of the Orkney Isles

Abstract

A patch of larval herring was located off the north coast of Scotland during early September 1986 and tracked for a period of 13 days by intensive surveying and deployments of drifting marker buoys. Two distinct cohorts of larvae were identified in the original patch, and a third, more recently hatched cohort became mixed with the other two along the drift trajectory. The length distributions of the larvae were analysed to produce growth rate estimates which were different for each cohort. Wind drag on the surface markers was shown to cause significant deviations between the trajectories of the larvae and the drifting buoys. A correction was applied to the buoy data to account for the wind drag, and, combined with data from a satellite-tracked ‘Argos’ buoy, indicated an average drift rate for the larvae of 9 km day −1 over a one-month period. The Argos buoy was carried from its release point off the west side of the Orkney Isles into the North Sea, passing through the Fair Isle Channel.