Relationships between daily growth of different groups of swordtip squid(Uroteuthis edulis)and environmental variables in the East China Sea

Swordtip squid(Uroteuthis edulis)is one of the important economical fishing target species in the East China Sea.Uroteuthis edulis is characterized by rapid growth,extensive migration,and long spawning period and sensitive to surrounding environment.In order to assess its stock status,it is necessary to explore its spawning season,growth patterns of different populations and their relationship with the environment in advance.In this paper,based on the samples of U.edulis collected in the East China Sea from September 2017 to March 2018,we explored the relationships between daily growth of statolith microstructure and environmental variables by gradient forest method and generalized additive model.The spawning season of U.edulis was found to be nearly one year,and two dominant season groups were found:the spring group with the peak period of April and the summer group with the peak period of August.Water temperature in the depth of 25 m(Temp_25),sea surface temperature(SST)and zonal velocity were the key environmental variables for the daily growth of April-spawning group.The most suitable environmental conditions for the growth of April-spawning group were water temperature(24-27℃)and velocity(0.1-0.3 m/s).SST,Temp_25 and mixed layer depth were the key environment variables for the daily growth of August-spawning group.The most suitable environmental conditions for the growth of Augustspawning group were water temperature(21-28℃)and water depth(0-50 m).Key environmental variables of different groups suggested that early growth was significantly affected by seasonal changes of water temperature,current velocity and prey abundance.This study explored the relationships between early growth and environmental variables and provided the scientific guidance for the management and conservation of U.edulis.