Relationships Of Stock And Recruitment In Fish Stock Assessment

In China, the dramatically increased fishing in the coastal and offshore area, and the pollution have led to the overexploitation of most of the commercially important species and the degradation of ecosystem. All these have negative effects on the sustainable exploitation of the fisheries resources in China. Therefore, it is urgent to make more effort to study the accurate stock assessment methods and their proper application in management, which can ensure the sustainability of marine fisheries in the 21 century in China.The precautionary approach in fisheries management has become a growing worldwide trend recently. Precautionary management reference points are those intended to prevent recruitment overfishing. Recruitment overfishing is defined as a state that the fish stock is exploited to a degree that its abundance is too low to keep equilibrium between reproduction and exploitation, recruitment is the basis for sustainable use of fisheries resources. At present, most of the marine fish stocks in China are in the state of recruitment overfishing. Since different stock-recruitment (SR) models can result in quite different estimates of management quantities, thus greatly affect the fisheries stock management and fish enhancement plans, consequently implementation of study on the relationship of SR and the SR based biological reference points are important.There are usually two steps in establishing an accurate and effective stock assessment model: first, choice of an assessment model; second, estimating the parameters in the selected model without error. However, large variations in recruitment, large measurement errors in spawning stock size (errors-in-variable), correlations between the present spawning stock size and previous recruitment values (time series bias), and large spatial distribution often cause large uncertainties (bias and variability) in parameter estimates. The determination of the SR relationship is perhaps among the most difficult tasks in fish stock assessment. This thesis mainly focuses on the selection of a suitable SR relationship,...