Role of shaded area under squid jigging boat formed by shipboard fishing light in the processes of gathering and capturing Japanese common squid, Todarodes pacificus

The behavior of Japanese common squid Todarodes pacificus under a squid jigging boat (research vessel Hakusan-maru, 167 gross tons) was investigated with echosounder and sonar during jigging operations in the Sea of Japan. Shipboard metal halide lamps (234 kW) were lit at night, and operations were conducted until enough squid had been gathered. Thereafter, an underwater light emitting diode lamp (600 W) was set under the boat and turned on/off. A shaded area was formed under the boat by the light of shipboard lamps, but it was partially eliminated and deformed by the light of the underwater lamp. Many squid were in the shaded area before the underwater lamp was turned on, but almost all the squid located near and above the lamp moved away from the area immediately after the lamp was turned on. Catch per unit effort (CPUE) decreased markedly while the underwater lamp was lit. Thereafter, when the underwater lamp was turned off, the squid immediately gathered in the shade area and CPUE also increased. These results indicate that the shaded area formed by the light of shipboard lamps gathers the squid under the jigging boat and helps to capture them.