Spatiotemporal spawning patterns and early growth of Japanese sardine in the western North Pacific during the recent stock increase

Spatiotemporal patterns in spawning of fish influence growth and survival by affecting the environment experienced offspring during their early life stages. Therefore, identifying changes can help researchers understand population dynamics recruitment fluctuations. The Japanese sardine Sardinops melanostictus is a small pelagic that undergoes large stock Although are known to change spatially temporally with abundance, little information available on processes underlying increases. This study aimed describe pattern recent period increase clarify effects different periods growth. We examined trends egg abundance western North Pacific 2004–2018 analyzed hatch dates trajectories otolith microstructure analysis juveniles from Kuroshio–Oyashio transition region (the species’ main nursery area). During period, area shifted eastern part this off Japan, roughly coincided juvenile dates. Hatch also mid-March at earliest February March 2013 onward. early-hatched cohorts (which originate offshore Japan) slower initial growth, they likely played an important role increase. Successful these may have been facilitated factors such as hatching transport nursery, which reduces frequency predator encounters.