Modelling the acoustic effect of swimbladder compression in herring

Abstract

Obtaining accurate data on fish target strength (TS) is important when determining the quality of the results from acoustic surveys. However, this requires an improved understanding of both behavioural and environmental influences on the acoustic backscattering by fish. It is well known that the increased pressure with depth compresses the swimbladder of herring, and it has been confirmed by in situ measurements that the TS of adult herring (30–34 cm) is 3–5 dB weaker at 300 m than that of fish close to the surface. Understanding exactly how swimbladder compression may influence herring TS is, therefore, of great interest, and is the main motivation behind this study. Taking account of swimbladder volume changes with depth, we obtained analytical solutions using the Modal-Based, Deformed-Cylinder Model (MB-DCM). The mean-backscattering cross-section is then computed with selected orientation patterns, length distributions, and contrast parameters. The depth-dependence of TS at different acoustic frequencies has been studied. We conducted a sensitivity analysis to show how TS is dependent on the contraction rates of the bladder dimensions and on the fish-orientation distribution. Our theoretical results are compared with TS measured at 38 kHz.

Instantaneous 3D Continental-Shelf Scale Imaging of Oceanic Fish by Multi-Spectral Resonance Sensing Reveals Group Behavior during Spawning Migration

“…The greatest differences in target strength between and within fish species typically occur at and below swimbladder resonance. Far less variation between and within species occur as frequency increases above swimbladder resonance and geometric scattering issues begin to dominate [34][35][36][37].…”

Differences in swimbladder volume between Baltic and Norwegian spring-spawning herring: Consequences for mean target strength

“…Details of the model routines can be found in Fässler et al (2007). The modal-series-based deformed-cylinder model (MSB-DCM) used to model the swimbladder is described in Gorska and Ona (2003a).…”

Simulations of multi-beam sonar echos from schooling individual fish in a quiet environment

“…In the simulation model, this equation is expressed as r 0 ðf 0 Þg C ¼ S m 10 À6:54 g C , where 40 ) is the long dimension of the prolate spheroid corresponding to swim bladder length. For values of kL ¼ 48:2, 49.2,…, 300.2, the method used by Tang did not perform satisfactorily, and estimates of the target beam pattern were calculated by use of the KRM model of a prolate spheroid despite its limited accuracy at large angles of incidence.…”