Dutch part of the international North Sea hydro acoustic survey for herring. The survey is coordinated by ICES and has been executed annually since 1991. Scotland, Germany, Denmark and Norway also participate in the survey. The purpose of the survey is to estimate the herring stock of the North Sea. The ICES Herring Assessment Working Group (HAWG) uses this estimation is as a "tuning index" to assess the North Sea herring stock. For this survey a Simrad 38kHz splitbeam transducer was used together with a Simrad EK60 echo sounder. The applied method was echo integration. By sailing transects over the survey area, the total acoustic cross-section can be calculated by surface area sampled. Trawling identified species composition of localized schools. The length composition of each species was determined. Herring and sprat were examined on age and fecundity from which a split up stock structure was made.
Henk J L Heessen (Netherlands Institute for Fisheries Research)
International Council for the Exploration of the Sea (ICES)