Study on the Geographic Variation and Trophic Variation of Todarodes pacificus in Different Areas Based on Stable Isotope Information from the Gladius

SIMPLE SUMMARY: Todarodes pacificus is an important cephalopod. This study analyzed the migration path and feeding ecology of T. pacificus by the stable isotope values of the proostracum of the gladius. This result showed that T. pacificus in the East China Sea migrated to low latitudes and nearshore areas during their life history, and the trophic level of their food exhibited no large changes during migration. T. pacificus in the Sea of Japan migrated to high latitudes and offshore areas during their life history, and the trophic level of their food decreased during migration. When the proostracum grew to 120 mm from the distal end, T. pacificus in both areas began to migrate. This study provides a scientific basis for further study on the fishery ecology and life history of T. pacificus. ABSTRACT: The Japanese flying squid (Todarodes pacificus) is an important cephalopod in the northwest Pacific Ocean. In this study, the proostracum of the gladius of T. pacificus samples collected by Chinese squid fishing vessels in the East China Sea and the Sea of Japan in August and December 2018 were continuously cut, and stable isotope values of the cut fragments were used to analyze the migration path and feeding ecology of T. pacificus. The results showed that when the proostracum grew to 120 mm from the distal end, T. pacificus began to migrate. In the East China Sea, T. pacificus migrated to low latitudes and nearshore areas, and the trophic level of their food showed no large changes during migration. In the Sea of Japan, T. pacificus migrated to high latitudes and offshore areas, and the trophic level of their food showed a decreasing trend during migration. There was no significant difference in migration or feeding ecology between females and males, but the competitive capacity of the females may be stronger than that of the males. The results provided a scientific basis for the scientific management and development of T. pacificus resources.