Population biological characteristics and resource exploitation status of Johnius belangerii in Zhanjiang Bay

Johnius belangerii is an important fishery resource in the Zhanjiang Bay, and its population and distribution have a significant impact on fishery production and ecological balance. We investigated the life history traits and exploitation status of J. belangerii in the Zhanjiang Bay based on data from bottom trawl surveys conducted during 2016–2021. ELEFAN I, Pauly's empirical formula and length conversion capture curves were used to estimate growth parameters and mortality rates. Virtual population analysis (VPA) and Beverton-Holt model were used to assess the exploitation status. The results indicate that the body length of J. belangerii ranged from 27.03 mm to 182.00 mm, with mass ranging from 0.19 g to 137.34 g. The estimated asymptotic length (L_∞) was 185.85 mm, the growth coefficient (K) was 0.61, and the theoretical age at growth (t₀) was –0.27. The total mortality coefficient (Z), natural mortality coefficient (M) and fishing mortality coefficient (F) are 2.40, 0.75, and 1.65, respectively. The current catchable size (83.74 mm) was significantly smaller than the optimal size (131.95 mm), suggesting a large composition of juveniles and a trend towards population miniaturization. The exploitation rate (E) of 0.69 exceeded the maximum sustainable rate (E_max=0.63), indicating a state of overfishing and extensive exploitation. The study reveals the life history traits of J. belangerii and provides insights into its sustainable management and conservation.