| Surplus production models are major academic models in assessment and management of modern fishery resources. Surplus production models can be simply used in fishery assessment because of their simplicity and relatively undemanding data needs, though fishery models are getting more and more complex. Surplus-production models are classical methods to predict the MSY (maximum sustainable yield) for fisheries management, which is still one of the major fisheries management goals. Despite the prevalence of a je-structured population models, surplus production models-which generally do not incorporate age structure-remains useful for fish population cynamics. These models are of particular value when the catch can not be aged, or can not be aged precisely, and therefore age-structured models can not be applied. Surplus-production models may be used as a kind of auxiliary implement to age-structured models, providing another view of the data and the fisheries.A continuous Schaefer-form production model, which was used in this thesis, was constructed by Prager (1994). This type prod action model has been applied in practical fishery assessment at abroad, but it was not systematically studied and applied to real fishery assessment at home.In this thesis, in order to find the necessary conditions and characteristics of data which can make the continuous Schaefer-form production model to get the best assessment results, the continuous Schaefer-form production model was used to analyze different simulated and real fisheries, and the assessment results were strictly analyzed.The Monte Carlo simulation study showed: when the white noise was smaller than 10%, the estimated values of all parameters were close to the ture values.Through statistical analysis to the assessment performance of model in four kinds simulated fisheries, it could be found that the assessment performance of model on "well managed" fishery was better than the other three fisheries, and the assessment performance of model on "under exploited" fishery was the worst. The possible cause was "well managed" fishery data contained more information because it experienced two periods, overfishing and restoring, however "under exploited" fishery data contained less information, these datum can't completely reflect dynamic change of fishery. The average values of estimation biases of four simulated fisheries respectively were: "one way trip" fishery 7.27%, "restoring" fishery 11.6%, "well managed" fishery 3.78%, "under exploited" fishery 15.9%. Check the deviation significance using ANOVA, it could be got: F=3.02, p=0.0018. According to research result above, it can be determined that if we want to get good assessment results when assessing fisheries using the continuous Schaefer-form production model, the fisheries must experienced overfished and restoring two phises, biomass fluctuated in large range and the fishery datum must be relatively precise.In comparison with effort level of about 70 x 106 (hooks/yr) in the early 1990s, estimation of the optimum fishing effort of 53.15x106 (hooks/yr) from the model showed that the swordfish, Xiphias gladius fishery in the North Atlantic Ocean had been overfished. From 1993 to 2001, the average Ishing effort of Scomberomorus niphonius (Cuvier et Valenciennes) fishery in Yai Tai city was 14791 boots/year, the average catch was 44837 tons. According to assessment result, the optimum fishing effort wasllSOO boots/year, the MSY(maximum sustainable yield) was 31522 tons, it was apparent that the two fisheries (swordfish, Xipl ias gladius fishery in the North Atlantic Ocean and Scomberomorus niphonius (Cuvior et Valenciennes) fishery in Yai Tai city) were overfished. In order to sustainably util ize and protect the two fisheries, strict control must be enforced on the fishing effort. |
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