Abundance estimation of schools using a fisheries sonar

An attempt of abundance estimation of fish schooling close to surface using sonar was conducted in Eastern North Sea - Skagerrak in September 1990. The method is based on measurements of the school area by the Furuno CSH-70 sonar and purse seine capture of schools to establish a school-area to school-biomass relationship. In the actual region, the biomass of herring and mackerel was estimated to about 90 000 ton and 430 000 ton, respectively. The accuracy of the method is discussed and improvements suggested