Target-strength estimates of schooling herring and mackerel using the comparison method

Abstract

The target strengths (TS) of schooling herring and mackerel have been estimated using the comparison method; purse-seine captures of schools measured by sonar and echo integration. For herring about 33 cm long, the results indicate an average TS of -40.8 dB, giving b= -71.1 dB as the constant in the usual TS equation (TS=20 log L+b). In the case of mackerel about 38 cm long, the average TS is -54.9 dB, which corresponds to b= -86.5 dB. The results are discussed in relation to other in situ estimates of the TS of these species. Limitations and inaccuracies in the applied method for TS estimation of schooling fish are also discussed. © 1996 International Council for the Exploration of the Sea.