Stock assessment of small yellow croaker in the East China Sea based on multi-source data

Abstract

Integrating the standardization of abundance indices into stock assessment models to examine the population dynamics of small yellow croaker, Larimichthys polyactis, was tested through a fisheries mixture matrix constructed with multiple data types. A precautionary approach to fishery control rules was adopted based on the logistic and Fox surplus production models, incorporating data from fishery-independent surveys, fisherydependent catch-per-unit-of-effort(CPUE), and regional harvests. A risk-averse control rule, derived from model parameters and associated uncertainty, was developed to manage fisheries for maximum sustainable yield(MSY)and rapid rebuilding of overfished stocks. The proposed control rule consists of relative biomass and relative fishing mortality rate in a deterministic environment and conservative harvest in a fluctuating environment. The results of the Fox model explained 68% of the variance observed for the stock abundance, while the logistic model explained 57%. The parameter estimates were different and the Fox model predicted a much larger decrease in population abundance at the MSY, intrinsic growth rates(r), and initial exploited levels. We compared the fishing mortality/current stock biomass from 1998 to 2006 with the fishing- and stock-related reference points, respectively. The results in a determined environment revealed that small yellow croaker stock in the East China Sea was overfished in most years, while the population was not always overfished during the entire period, although its biomass has been decreasing since 1999. However, both the Fox and logistic surplus production models indicate that the small yellow croaker fishery has been consistently over harvested in the fluctuating environment. Harvesting at a conservative level with either the Fox or logistic model could increase small yellow croaker abundance substantially with little decrease in harvest. At a conservative harvest level, there is a 24.7% increase in biomass with a 6.1% decrease in yield with the logistic model and a 44.5% increase in biomass with a 9.4% decrease in yield with the Fox model. The MSY assessment results from the Fox surplus production model was more conservative than that of logistic model, which is concordant with precautionary fisheries management strategies.