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標題: | 生態競爭對用貝氏估計生產量模式評估大西洋黃鰭鮪與大目鮪資源的影響 Effects of Ecological Competition on Assessing Yellowfin tuna (Thunnus albacares) and Bigeye tuna (Thunnus obesus) Stocks in the Atlantic Ocean by Production Model with a Bayesian Approach |
作者: | Chia-Lung Shih 石佳隴 |
指導教授: | 許建宗 |
關鍵字: | 生態競爭,delta泛線性模式,象平面分析,標準化豐度指標,總可漁獲量, ecological competition,delta generalized linear model,phase plane analysis,standardization abundance index,total allowable catch, |
出版年 : | 2014 |
學位: | 博士 |
摘要: | 大西洋黃鰭鮪與大目鮪主要棲息在熱帶海域,產卵場皆在新幾內亞灣夏季產卵,且稚魚階段混游在表水層。再則,胃內容物研究顯示此兩系群彼此間食性重疊。因此推測此兩魚種系群可能彼此間有生態競爭的影響。本研究目的是利用生產量模式評估競爭對大西洋黃鰭鮪與大目鮪資源之影響。台灣延繩釣漁獲統計資料顯示,漁業可分為兩種作業型態。一種是採用每筐鉤數比較少(8-11鉤)的作業型態,主要作業於緯度較高的海域(15oN以北與20oS以南),以捕獲長鰭鮪為主,此種作業型態稱為傳統式延繩釣。另外一種採用每筐鉤數較多(15-18鉤)的作業型態,主要在熱帶海域作業(15oN-20oS),以捕獲大目鮪為主且容易混獲大量黃鰭鮪,此種作業型態稱為深層式延繩釣。台灣延繩釣是主要捕獲大西洋大目鮪與黃鰭鮪重要漁業國家之一。本研究利用台灣延繩釣漁獲統計資料進行標準化大目鮪與黃鰭鮪CPUE序列。標準化黃鰭鮪與大目鮪CPUE序列在1994與1995年出現極高值,且隨時間序列變異很大。利用貝氏法估計生產量模式參數的敏感度分析中,發現不合理先驗參數設定範圍與有問題的國家漁業CPUE序列對資源評估影響很大。當輸入資料含有台灣延繩釣大目鮪CPUE序列時,會造成估計參數差異變大。評估黃鰭鮪與大目鮪彼此競爭對資源的影響,結果發現此兩系群彼此間存在競爭影響。黃鰭鮪系群會明顯降低大目鮪系群資源量(w2=0.2304),而大目鮪系群對黃鰭鮪系群的抑制影響很小(w1=0.0981)。比較模式是否有考慮競爭參數所估得生物參考點的差異,當模式考慮競爭參數時黃鰭鮪與大目鮪的估計值變小,其中大目鮪在考慮競爭參數模式下的最大持續生產量(7.3萬公噸)比未考慮競爭參數估值(最大持續生產量: 9.5萬公噸)小很多。本研究建議每年可捕獲量,黃鰭鮪可維持在目前漁獲量(11萬公噸),但大目鮪需由歷年設定的8.5萬公噸調降到4萬公噸,以避免過度利用此資源。 Yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) stocks in the Atlantic Ocean are mainly distributed in the tropical waters. These two stocks spawn in the Gulf of Guinea during summer. When they are in their juvenile stage, these two stocks mix in the surface waters. In addition, the stomach contents of these two stocks show dietary overlap. Thus, we hypothesized that these two stocks may show the effects of ecological competition on both. The objective of this study is to investigate the effects of ecological competition on assessing yellowfin tuna and bigeye tuna stocks by using the surplus production model with a Bayesian approach. In the analysis of Taiwanese longline fishery data, the results showed that there were two fishing types in the fishery. One fishing type was using lower number hooks of per basket (8-11 hooks), operating majorly in the higher latitude of waters (north of 15oN and south of 20oS), targeting on albacore and called as regular longline fishery. Another fishing type was using higher number hooks per basket (15-18 hooks), operating majorly in the lower latitude of waters (15oN-20oS), targeting on bigeye tuna and bycatching yellowfin tuna, and called as deep longline fishery. The standardized yellowfin tuna and bigeye tuna abundance indexes of this study showed extreme high CPUEs in 1994 and 1995, and highly temperal variation. In the sensitivity analysis of Bayesian approach, the results showed that unreasonable priors setting and questionable country fishery abundance indexes would result in bias of stock assessment. While input data included bigeye tuna abundance indexes of Taiwanese longline fihsery, the estimated parameters of production model showed a slight diference. In the analysis of the effects of competition on assessing yellowfin tuna and bigeye tuna stocks, the results showed that the competition exist in the two stocks. Yellowfin tuna stock could obviously decrease the biomass of bigeye tuna stock (w2=0.2304) and bigeye tuna stock would lightly decrease the biomass of yellowfin tuna stock (w1=0.0981). The estimated parameters of yellowfin tuna and bigeye tuna stocks estimated by the model with competition became smaller than these estimated by the single-species model, but the maximum sustainable yield (73,000 tons) of bigeye tuna estimated by the model with competition were smaller than that (maximum sustainable yield: 95,000 tons) estimated by the single-species model. Thus, we suggested that the total allowable catch of yellowfin tuna stock could be maintained at the current catch level (110,000 tons), whereas that of bigeye tuna stock should be decreased from 85,000 tons to 40,000 tons to avoid overexploiting this stock. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/16656 |
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顯示於系所單位: | 海洋研究所 |
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