Low frequency acoustical scattering from dynamic schools of swim bladder fish

Abstract

A time-domain computational model is used to describe the dynamic evolutions of fish schools. The individual and ensemble fish behaviors are governed by three radial parameters, representing attraction, orientation, and repulsion zones between fishes. Different combinations of these radii cause the schools to evolve into various discoid, swarming, parallelized, or toroidal geometric forms. A previously developed model [J. Acoust. Soc. Am. 99, 196–208 (1996)] is applied to study the variations in ensemble scattering from these school types for ensonification frequencies in the swim bladder resonance region, as a function of frequency and time, and predicts distinct characteristic features for the different school geometries. In particular, this work focuses on scattering from disk-shaped schools, by examining the computed resonance response for different school dimensions, packing density, and orientation, in order to identify specific features that are determinative for this type of arrangement. The ultimate goal of this work is to achieve a better understanding of the physical basis for variations in fish school scattering levels and to obtain a detailed statistical description of these objects. [Work supported by ONRG.]