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MEPS prepress abstract   -  DOI:

Long-term comparison between the Japanese sardine (Sardinops melanostictus) stock level and simulated zooplankton density around the Kuroshio region

Haruka Nishikawa*, Hiroyuki Tsujino, Shiro Nishikawa, Shin-Ichiro Nakayama, Hideyuki Nakano, Toru Sugiyama, Yoichi Ishikawa

*Corresponding author:

ABSTRACT: Sardine species are known for the multi-decadal scale stock fluctuation. The Japanese sardine (Sardinops malanostctus) is one of such sardine species and distributed near the western boundary current system, Kuroshio. Like other sardines, food availability in the larval stage is thought to be an important factor for the Japanese sardine stock fluctuation. Previous studies have suggested the significance of the feeding environment, particularly in the winter and spring seasons, within the Kuroshio axis area. However, collecting zooplankton, the primary food for larvae, along the strong current is challenging, and there is a lack of long-term observational data on zooplankton in this area. Therefore, this study estimated zooplankton density in the Kuroshio axis area from 1967 to 2018 using a lower trophic level ecosystem model and compared it with the logarithm of recruitment per spawner (LNRPS) and logarithm of recruitment per egg (LNRPE) of the Japanese sardine. A significant correlation was found between the zooplankton density and LNRPS from 1967 to 2004 and a significant correlation was found between the zooplankton density and LNRPE in certain periods (1979–1996). Since the Granger causality was established between zooplankton density and LNRPS before around 2005 and between zooplankton density and LNRPE before 1996, in these periods, there is a high likelihood that zooplankton density is influencing the recruitment interannual variation. On the other hand, there was no relationship between recent food availability and LNRPS/LNRPE. This aspect remains a subject for future research.