Abstract: Decapterus maruadsi is an important small pelagic fish species in the South China Sea. Effective assessment of stock status and formulation of management recommendations based on the best available science are urgently needed for the conservation and sustainable development of this species. Based on the Bayesian state space modeling framework, we assessed the stocks of D. maruadsi by integrating a surplus production function with fishery production data to establish a baseline assessment scenario. The results showed that the evaluation scheme constructed based on the Fox surplus production function and fishing vessel power exhibited the best fitting effect. The results derived from this scheme indicated that the fishing intensity of D. maruadsi population in the South China Sea initially increased and then decreased from 1990 to 2023, yet it remained at a relatively high level. Overall, the biomass showed a fluctuating downward trend. During the model evaluation period, the maximum sustainable yield (MSY) of D. maruadsi was estimated to be 497000 t. The biomass required to maintain MSY and fishing intensity required to maintain MSY were 644000 t and 0.79, respectively. In 2023, the biomass of D. maruadsi population in the South China Sea was 688100 t, which was greater than that required to maintain MSY. The fishing intensity was 0.52, which was lower than that required to maintain MSY. It was determined that D. maruadsi population in the South China Sea did not experience overfishing in 2023 and was at a healthy state. The prediction results showed that fishing at a limit of 120% of the 2023 catch (i.e., 427000 t) would result in an upward trend in biomass over the next decade. The sensitivity analysis results indicated that increasing the prior mean values of the population parameter initial resource consumption rate (P₁₉₉₀) and environmental carrying capacity would lead to an overestimation of biomass and an underestimation of fishing intensity, with P₁₉₉₀ having a more significant impact. In summary, the residual yield model based on Bayesian state space was suitable for the assessment of fishery resources of D. maruadsi in the South China Sea under limited data conditions. It was recommended to set the total allowable catch of D. maruadsi in the South China Sea at 427000 t, conduct continuous monitoring, and regularly update assessment results to improve resource conservation and management effectiveness.

Key words: Decapterus maruadsi, surplus production model, population dynamics, catch limit