Three dimensional observation of pelagic fish schools by multibeam echosounder ME70

In this study, three-dimensional observation of pelagic fish using a multibeam echosounder with a quantitative echosounder are discussed. Multibeam echosounder originally has been developed for bathymetry survey, transmits and receives fan-shaped acoustic beam, and has extensive search area compared with single beam conventional echosounder. SIMRAD ME70 used in this study was developed specifically for fisheries research while maintaining the characteristics of fan-shaped wide multibeam. Because the calibration software is built in the ME70 for quantitative analysis of the acoustic beams, the output data can be compared with that from the quantitative echosounder like the EK60. Therefore, the ME70 and the EK60 are installed in the R/V YOKO-MARU used in alternate transmission, and carried out the observation for the same fish schools. Echograms were obtained from both echosounders and compared in terms of differences in characteristics of these echograms. Multibeam echosounder covered a widespread area to the side way of the vessel that the conventional echosounder could not observe and allowed to express fish schools in three dimensions.