From two dimensions to three: the use of multibeam sonar for a new approach in fisheries acoustics

We present a methodology applying multibeam sonar for three-dimensional (3D ) observation of fish schools that enhances the conventional use of vertica l scientific echo sounders. The sonar we employ has 60 beams of 1.5 degrees each. Its working frequency is 455 kHz. It is applied on a vertical plan n ormal to the vessel route, observing from the surface line to the bottom wi th a range set to 100 m. The sampled volume is 14 times larger than the vol ume observed with vertical echo sounding. The contribution of this new meth odology to fisheries acoustics is detailed for school classification, inter nal school structure, spatial distribution of schools, fish behaviour, and biomass estimates. For each of these points, we present some preliminary re sults with the aim of defining the real progress in fisheries acoustics res earch as a result of 3D acoustics. Finally, we present a list of technical and methodological improvements that we are developing in order to make mul tibeam sonar fully adapted to fisheries acoustics.