Horizontal target strength of Cyprinus Carpio using 200Â kHz and 430Â kHz split-beam systems

Horizontal hydroacoustics is a useful tool to study fish in shallow waters and complete the density and biomass estimates calculated from vertical hydroacoustic samplings. In order to properly interpret the information obtained from acoustic studies, previously established equations that relate the fish's backscattered sound or target strength (TS) to its biological parameters such as length or weight are used. For freshwater species, these relationships are scarce and those that are already published differ in terms of acquisition systems (single, dual or split-beam; frequencies; manufacturers), acquisition methodology (recording settings, immobilised or free-swimming fish, etc.) or species and sizes.In this study, conversion equations for the species Cyprinus carpio using two different split-beam systems operating at different frequencies (200 and 430 kHz) have been developed. These split-beam equations have been compared between both frequencies and they have also been compared with other equations previously published for dual-beam systems. The results show that the applied equation has an influence on the results and the differences are greater when comparing split and dual-beam systems than when comparing the split-beam equations obtained at different frequencies. These comparisons help us establish criteria to determine the best equation to analyse our results in hydroacoustic surveys and allow us for a more appropriate interpretation of the information obtained from acoustic samplings. Moreover, this study is important to perform inter-calibration exercises as well as to establish the foundations for the standardisation of fish samplings using hydroacoustics.