Distribution patterns of the Japanese common squid, Todarodes pacificus attracted around the luring lamp on the jigging boat
This study investigated luring distributions by water layer of common squid which were targeted by angling fishing vessels equipped with LED and metal-halide lamps using a scientific echosounder with a 120 kHz frequency in order to develop energy-effective underwater fish aggregation devices. In the analysis, angles of a transducer were changed from 0° to 45° and were rotated every 10° horizontally. It was shown that common squid were densely distributed from the surface to 40 m and they were also distributed in directions of 10°∼+30°, -30°∼-60°, and -120°∼-130°with the head of vessel as the center. Comparative results of angles of transducer on acoustical densities of common squid distributing in 21~40 m water depth showed an average 101.8 m2/nm2 in vertical direction of 0°, 12.3 m2/nm2 in angle of 30°, and 42.4 m2/nm2 in angle of 45°, respectively. It implied that more considerations on acoustic scattering strength by incidence angle direction of the transducer and swimming oriental angle direction of common squid would be required.