Migration and schooling dynamics of herring and capelin during the spawning season - Impact on stock assessment

The assessment of Norwegian spring spawning herring and Barents Sea capelin is largely based on acoustic abundance estimates from the feeding season (both species) and wintering season (herring). There is a potential for improved assessment by estimating these stocks also during the spawning season. Due to extensive migrations and schooling dynamics during this period, there is need for increased knowledge of their behaviour in order to design appropriate surveys and obtain reliable abundance estimates. The present project will describe and quantify the migrations and schooling dynamics of herring and capelin during the spawning season, with special emphasis on biomass flux and diurnal variations in schooling behaviour. The stocks will be studied both d u ring migration towards the spawning grounds and at the spawning grounds. Analyses of schooling behaviour will be based on acoustic recordings of school packing density, size, vertical position in the water coumn and the cluster patterns, focusing on the mechanisms behind the observed behaviour. The fish distribution and movement will be modelled and different survey strategies simulated to obtain optimal survey designs that could be applied in future acoustic abundance estimation.