1Ishikawa Prefecture Fisheries Research Center, Housu, Ishikawa 927-0435, 2Towa Denki Seisakusho Co., Ltd., Hakodate, Hokkaido 040-0077, 3National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki 314-0408, Japan
The behavior of Japanese common squid Todarodes pacificus around a squid jigging boat during night-time operation was investigated. Eighty-nine operations were conducted by R/V Hakusan-Maru (167 gross tons) equipped with 78 metal halide lamps (234 kW in total) in offshore fishing grounds in the Sea of Japan, and sonar images and squid catch were continuously recorded (logged). The positions of squid schools before they were caught were tracked from sonar image recordings using digitizer software. Squid schools moved around the boat, gradually approached the boat and then tended to locate in fore and aft areas just before they were caught. More squid were caught by jigging machines near the bow or stern than by those near the center of the boat. Underwater irradiance was lower in fore and aft areas than in port and starboard areas. These results indicate that squid schools tended to enter under the boat through fore and aft areas. Namely, fore and aft areas with low irradiance are thought to function as an entrance to the shaded area under the boat for the squid.