A model for estimating distributions of fish school target strengths

Abstract

A model has been developed to estimate the distribution of fish school target strengths for any schooling species. The model has both biological and acoustic components. The biological component estimates distributions of school size and density for a given species. A discrete spectrum of non-dimensionalized school densities, developed by combining and synthesizing the results of experimental studies on intra-school spacing, is used to estimate school density distributions. Discrete spectra of school sizes based on empirical knowledge and assumptions of school growth and reduction are used to estimate school size distributions. The acoustic component combines estimates of target strengths of individual fish with numbers of fish insonified to calculate school target strengths at any aspect for a school of given size and density. Multiple scattering and attenuation through the school are taken into account. Provision is made for schools that are not totally insonified due to limitations of sonar beam width or pulse length. Comparison with available experimental data indicates that the model produces a realistic estimate of target strength distributions.