Climate-Related Variations in Autumn Cohort of Japanese Common Squid Todarodes pacificus

The Japanese common squid Todarodes pacificus is widely distributed in the Sea of Japan, the East China Sea and the Northwest Pacific Ocean, and is largely exploited by the Asia-Pacific countries. In this study, the impacts of regime shift of the Pacific Decadal Oscillation (PDO) during 1977–2015 on the autumn cohort of T. pacificus were assessed by examining the variations in vertical water temperatures at depths of 0 m ( Temp _0 m), 50 m ( Temp _50 m) and 100 m ( Temp _100 m) and the distribution pattern of preferred spawning ground (SSG). Spatial and temporal correlation analysis revealed that the PDO index exhibited a significantly negative relationship with vertical water temperatures at different depths and was negatively related to catch-per-unit-effort ( CPUE ) and stock biomass of T. pacificus . In addition, water temperatures in the specific three water layers were positively associated with CPUE . The PDO regime shift strongly affected the thermal condition and spawning ground of T. pacificus . Comparing to the negative PDO, the waters from the surface to the deep became cool in the positive PDO phase; correspondingly, the area of SSG largely contracted at different depths. Consequently, the CPUE and stock biomass of T. pacificus profoundly decreased. From the results it can be concluded that the PDO regime shift-driven changes in vertical thermal condition and SSG ranges can yield substantial impacts on T. pacificus abundance.