| 英文摘要 |
Fishery managements are established on the basis of biological reference points and their life parameters, and the estimated abundance indices obtained from data of commercial fisheries are the general ones in assessments. Taiwanese longline fishery contributes a very long historical operation and catch data bases itself, meanwhile it is also expected to standardize its catch per unit effort for target species to be served as one of abundance indices in assessments. Bigeye tuna is a species of tropical tunas and contributes the highest production value worldwide recently. Taiwanese longline fishery started to target this species by 1990 and produced over than 10,000 annually since then. However, standardized catch per unit effort for bigeye tuna by Taiwanese longline data set has not displayed coincident trend with abundance changes and catch trends. The report is attempting to investigate the problems of Taiwanese longline fishery data bases in using the daily logbooks submitted by national fleet, in which contain the catches by vessels, abundance distribution and the characteristics of standardizing models for commercial fisheries. Through analyses of Taiwanese longline data bases targeted bigeye tuna in the Atlantic, the results indicated that the questionable problems showing in these logbooks include too many zero catch record in all, too many operation days, too many daily lifted hooks over a possible manpower load, too large discrepancies between catch estimates and catch reported, distribution of nominal catch per unit effort by vessels did not confront the assumed model, and severely, too large magnitude of the parameters of median and variance of lognormal distribution. Based on these facts, the assessment may over-estimate the parameters of population dynamics and may obtain a high uncertainty of estimated biological reference points in situ when Taiwanese longline fishery data bases were used in stock assessment for the bigye tuna stock in the Atlantic Ocean. |