Effects of environmental variability on the spawning areas, catch, and recruitment of the Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae), from the 1970s to the 2000s

摘要

The Japanese common squid, Todarodes pacificus, is one of the most commercially valuable squids in the world. It spawns almost throughout the year, with a seasonal peak in autumn and winter. Long-term changes in sea surface temperature (SST) and its effect on the spawning areas and catch of T. pacificus were analysed for 27 spawning seasons (September- April 1978 - 2006) in the Sea of japan and East China Sea. The spawning area was inferred between the limits of 21 -41 °N and 121 ° - 142°E, 100-500-m depth, the mean Kuroshio axis, and the 19.5 -23°C SST range. The results revealed that the area surrounding Kyushu Island is gaining importance as a spawning area. In addition, the discontinuity of the spawning ground in the East China Sea (around 29°N 128°E) during the winter spawning period was demonstrated to be associated with a decrease in the catches by both the Japanese and the Korean fleets. This constriction of the spawning ground would act as an obstacle to either the adult squid, making it difficult for them to reach the most southern grounds, or the para-larvae and juveniles, which, because of adverse environmental conditions, might not be able to survive the early stages of the feeding migration.