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

概要

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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 to 2006) in the Sea of Japan and East China Sea. The spawning area was inferred between the limitations of 21°-41°N and 121°-142°E, the 100-500m depth, the mean Kuroshio axis, and the 19.5°-23°C SST range. The results showed that the area surrounding Kyushu Island is gaining importance as a spawning area. Also, the discontinuity of the spawning ground in the East China Sea (around 29°N 128°E) during the winter spawning period was shown 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 hatchlings, which, due to adversary environmental conditions, may not be able to survive the early stages of the feeding migration.