碩士 / 國立臺灣大學 / 海洋研究所 / 100 / Surplus production models have been used in fisheries stock assessment for more than a half century. These models simply pool the overall effect of growth, recruitment, and mortality into the productivity function, and just use simple data. But these three surplus components may be with different effect on the productivity, and the biological or ecological factors influencing the productivity may also be diversified. All of those diversified factors may be called “ecological uncertainty”. Some scientist introduces reconstructing surplus production models to address the ecological uncertainty. But in the actual stock assessment, it does not take the ecological uncertainty into account. Use the Schaefer model, one of the classic surplus production models, as the baseline model. And the production model with ecological uncertainty refers to the study of Johannesen and Skonhoft (2009). As they formulated, ecological uncertainty was captured by the random variable. The Atlantic Ocean bigeye tuna (Thunnus obesus) fishery was used as example to demonstrate the baseline model and the production model with ecological uncertainty, and the data was from 1961 to 2008. For the baseline model, the estimated parameters were r=0.19 and K=1,530,000 tons. Biological reference points were MSY=74,200 tons, F2008/FMSY=1.326. For the production model with ecological uncertainty, the estimated average MSY was about 66,700 tons and F2008/FMSY=1.43. The total catch of the Atlantic bigeye tuna was larger than the MSY in 2008. As the Kobe matrix illustrates, both the result of the baseline model and the production model with ecological uncertainty, the Atlantic Ocean bigeye tuna stock is overfished and overfishing in the last few years. And the Kobe matrix also shows the upward shift from the baseline model to the production model with ecological uncertainty. It implies that when take ecological uncertainty into account, the status of the stock is more likely to be overfishing than the baseline model. Therefore, the reduction of the Atlantic bigeye tuna catch quota is necessary to make the bigeye tuna stock status become healthier.
| Identifer | oai:union.ndltd.org:TW/100NTU05279009 |
| Date | January 2012 |
| Creators | Fang-Chi Hsueh, 薛方琪 |
| Contributors | 許建宗 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 56 |
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