Modelling herring target strength pressure dependence in the frequency domain

Abstract

Improved understanding of the acoustic scattering properties of the fish is needed when trying to remove potential bias is acoustic abundance estimates. The paper address the problem of systematic pressure or depth dependency in herring target strength, as due to the uncompensated compression of the swimbladder with depth. As a first stage, a theoretical approach to the problem is developed using a Modal-Based Deformed Cylinder Model. This includes the pressure effects on the swimbladder and the effect of the fish flesh. Using the theoretical solutions obtained, a sensitivity analysis on fish target strength with pressure is made at various acoustic frequencies, and compared with real target strength data on adult herring.