Growth, maturity and mortality of Johnius distinctus and J. belangerii in offshore waters of southern Zhejiang Province

Karut croaker (Johnius distinctus) and Belanger's croaker (J. belangerii) are common small economic fishes and important prey species in the ecosystem of the East China Sea. Studies on their biological characteristics are essential to understand the ecosystem and to improve the scientific management of these important fisheries in the East China Sea. Based on the seasonal surveys of fishery resources in the offshore waters of southern Zhejiang Province, we applied linear mixed effects model (LMEM) to study the growth characteristics and heterogeneity of the two species. The asymptotic body length (L_∞), growth rate (k) and theoretical growth starting age (t₀) were estimated by ELEFAN method. The natural mortality coefficient (M), total mortality coefficient (Z), development rate (E), and the 50% sexual mature body length of the two species were estimated. The LMEM results show that seasons have the most significant effect on their growth. For J. distinctus, L_∞=216.83 mm, k=0.84, t₀=−0.18; for J. belangerii, L_∞=207.38 mm, k=0.63, t₀=−0.25. For J. distinctus, Z=3.80, M=1.53, E=0.60; for J. belangerii, Z=1.88, M=1.24, E=0.34. The length of 50% maturity's estimates were 133.1 mm and 128.9 mm for J. distinctus and J. belangerii, respectively.