Relationship between recruitment of Japanese sardine (Sardinops melanostictus) and environment of larval habitat in the low‐stock period (1995–2010)

Abstract

AbstractStock level of Japanese sardine (Sardinops melanostictus) was high from 1980s to early 1990s and low from late 1990s to 2000s. The warm and cold water masses in the vicinity of the Kuroshio axis from winter to early spring used to be critical for the recruitment in the high‐stock period, because most of the larvae were distributed there. However, the environmental fluctuation might not affect the recruitment in the low‐stock period. Some studies reported that spawning location and spawning season, and hence the larval habitat, differ depending on the stock level. Three points were investigated in this study: (a) how spawning location and spawning season shifted from the late 1990s, (b) confirmation of the distribution area of larvae in the recent low‐stock period and (c) whether the water temperature in the vicinity of the Kuroshio axis was still related to the recruitment in the low‐stock period. The spawning location and spawning season clearly changed after 1995. Consequently, particle tracking experiments suggested that the larvae appeared in the vicinity of the Kuroshio axis from winter to early spring decreased. Nevertheless, only the ambient temperature of larvae that appeared in the vicinity of the Kuroshio axis from winter had a significant negative correlation with an index of the recruitment in the low‐stock period. It is suggested that the warm and cold masses in the vicinity of the Kuroshio axis are critical for the recruitment regardless of the stock level.