Characterization of European sprat acoustic backscatter through modeling techniques: A comparison with in situ observations in the Mediterranean Sea

Abstract

In fisheries acoustics, the identification of targets and the precise conversion of acoustic energy into biologically important meaningful metrics remain a challenge. Backscattering cross-section, or its logarithmic form, Target Strength (TS, dB re 1 m²), is a key parameter in this process. While numerous studies exist on the TS of commercially important species, there is a paucity of research on commercially ancillary species, such as the European sprat in the Mediterranean Sea, which is nonetheless of great importance for the pelagic ecosystem. The application of backscattering models can enhance our understanding of this species’ acoustic properties. In this study, we applied several backscattering models on three-dimensional swim bladder shapes derived from Computer Tomography (CT) scans of sprat collected during the MEDiterranean International Acoustic Survey (MEDIAS). The theoretical TS pattern was compared with empirical empirically TS measurements, demonstrating a good fit at 38 and 70 kHz between 0° (broadside incidence) and −20°. Significant differences were observed at higher frequencies and tilt angles. This study provides estimates of the relative frequency response and broadband backscatter of sprat in the Mediterranean Sea. We proposed a new relevant TS to length relationship of 20 log(L)-68.3 dB re 1 m² at 38 kHz for European sprat in the Mediterranean Sea.