The rapid expansion of yellowtail (Seriola quinqueradiata) spawning ground in the East China Sea is linked to increasing recruitment and spawning stock biomass

Abstract

Abstract Biomass of the yellowtail Seriola quinqueradiata, an important fishery resource in Japan, has increased about threefold over the past 20 years to ∼300 thousand metric tons. We examined the interannual variations in distribution and abundance of S. quinqueradiata larvae [4.2–7.9 mm body length (BL), ∼7 to 18 days after hatching], based on sampling surveys over a broad area of the shelf-break region of the East China Sea (ECS) in April, the main spawning period, over 15 years (2001–2015). High abundances of larvae were found in the northern ECS off the southwestern coast of Kyushu Island throughout the survey period. After 2010, the larvae began to occur abundantly also in the southern ECS south of 29°30′N, indicating a southward expansion of the spawning ground. There has been a significant positive trend of larval abundance over the whole ECS during the 15 years, which was mainly due to the sharp increase in larval abundance in the southern ECS after 2010. Although interannual variation in larval abundance was not related to environmental conditions (temperature, salinity, and chlorophyll a concentration), it was closely correlated with the spawning stock biomass. This indicates that the increasing trend of larvae was related to the increase in egg production in the ECS. Also, the larval abundance showed a weak positive correlation with recruitment, suggesting that the increased larval abundance has, in part, contributed to high recruitment.