イカ釣り漁業におけるスルメイカの誘集･漁獲過程に関する研究

抄録

In order to elucidate the process of gathering and capture of Japanese common squid Todarodes pacificus, night-time squid jigging operations were conducted by R/V Hakusan-maru （167 gross tons） equipped with 78 metal halide lamps（ 234 kW in total） in the Sea of Japan. The behavior of the squid and the changes in catch per unit effort（ CPUE） and density of the squid under the vessel were investigated during each operation. The following results and conclusions were obtained: （1） Squid schools moved around the high-irradiance area formed along port and starboard side of the vessel, and tended to locate in fore and aft areas just before they were caught. Therefore, fore and aft areas with low irradiance are thought to function as an entrance to the shaded area under the vessel for the squid.（ 2） When the shaded area was eliminated and deformed by lighting of underwater lamp, the squid moved away from the area under the vessel and CPUE decreased. Thereafter, when the underwater lamp was turned off, the squid immediately gathered under the vessel and CPUE increased. These results indicate that the shaded area is essential for gathering the squid under the vessel and capturing them. （3） CPUE increased with increasing squid density, but the extent of the increase of CPUE greatly differed by operation. When CPUE was extremely high, the increase of CPUE slowed down. The relationship between CPUE and squid density （S） was expressed as CPUE=A･S/（B− 1+S）, where A is an upper limiting CPUE and B is catchability of the squid. Furthermore, B was found to vary greatly among operations. For this reason, it was thought that higher squid density does not necessarily bring about more catch.