On the target strength of Baltic clupeids

Fässler, S. M. M., and Gorska, N. 2009. On the target strength of Baltic clupeids. – ICES Journal of Marine Science, 66: 1184–1190. The acoustic backscattering of Baltic clupeids, herring and sprat, is explored to improve biomass estimation of these ecologically and commercially important species. Modelling approaches that account for the complexity of fish morphology are used to compute the mean backscattering cross section. The input data for modelling are based on X-ray radiographs of Baltic herring and sprat. The backscatter sensitivity to fish morphology and to other biological (fat content), acoustic (frequency), behavioural (orientation pattern), and environmental (depth and salinity) parameters is also analysed. The effect of various parameters on the TS–L relationship of Baltic clupeids is studied, and the possibility of using the same TS–L relationships for Baltic herring and sprat is discussed. The results improve the understanding of the spatial and temporal variability of the measured target strength of clupeids in the Baltic Sea.