Estimations Of Biological Reference Points And The Application Of Them In The Stock Assessment Of The Hairtail (Trichiurus Haumela) Fishery In The East China Sea

The status of the hairtail (Trichiurus haumela) fishery in the East China Sea has not been quantitatively determined using biological reference points, despite its commercial importance and declining stock abundances since the mid 1990s. This is an attempt to incorporate uncertainty into the estimation of F_0.1 and F_max and make utilization of them in the fishery management. We incorporated random variation to simulate uncertainties in the fishery data. The results showed that high levels of uncertainty increased variations in F_0.1 and F_max estimation, which led to a decrease in the probability that the fishery was defined as overfished. We then compared current fishing mortality Fcur with F_0.1 and F_max and found that the hairtail fishery is being overexploited. The changes of catches at various tc revealed that increasing tc reduced the probability that Fcur is greater than FBRP, for which we concluded that increasing tc can improve the stock status of the hairtail fishery.China officially announced Summer Fishing Moratorium in the waters of the East China Sea in 1995. Although Summer Fishing Moratorium was implemented twelve years ago, its effective evaluation has not been quantitatively conducted through the utilization of biological reference points. The estimation results of the population parameters of the hairtail are used in the yield per recruit model, spawning biomass per recruit model, and spawning fecundity per recruit model to evaluate the impact of Summer Fishing Moratorium. The effect of Summer Fishing Moratorium was evaluated through calculating the changes of F_0.1, F_max, F30%, F40%, and Fcun20% and variations of yield, spawning biomass, spawning fecundity per recruit with the Beverton-Holt model. The results show that the moratorium has achieved relatively good ecological and biological benefits. The system has led to the increased yields, number of juvenile fish, and spawning fecundity of hairtail fishery in the East China Sea. However, this positive effect decreased with the increase of the age at first capture (tc) and the yields, spawning biomass, and spawning fecundity per recruit are relatively low.The first part of the thesis reveals that uncertainties will influence the estimation of biological reference points F_0.1 and F_max , which can lead to negative effect to the stock assessment of the fishery. So it is necessary and essential to incorporate uncertainties into the assessment process to quantitatively and precisely evaluate fishery stock. Results of the evaluation of Summer Fishing Moratorium suggest that the management measure has a number of limitations under current fisheries situation. Thus, we proposed that the fisheries management in the East China Sea in the future ought to implement the Summer Fishing Moratorium as a leading fisheries management measure combining with management of increasing age at first capture so that the sustainable development of the hairtail fisheries can be achieved.