Effect of swimming on fish target strength

The influence of the swimming movement on fish target strength is investigated through a modelling exercise. In this, several gadoid specimens are represented as acoustic scatterers through their triangulated swimbladder surfaces, assumed to be perfectly pressurereleasing. The swimming movement is described as a periodic deformation in swimbladder shape consistent with actual measurements of whole-body movements of swimming gadoids. Results of computations of target strength as would be observed with a vertical echo sounder are expressed through the probability density function. This is found to be nearly identical to that of the same fish with normal extended posture. The inconsequentiality of swimming movement to the target strength in typical echo-sounding applications is thereby demonstrated