Analysis of seabird bycatch of Taiwanese longline in the Pacific Ocean.
研究生: 陳翊蓁 Yi-Jen Chen
近年來漁業行為對海洋生物多樣性的影響，已引起諸多關切。延繩釣漁船於佈餌時，海鳥會伺機衝向魚餌搶食而被魚鉤鉤到，造成海鳥傷亡而影響其生物資源量。本研究針對太平洋台灣鲔延繩釣漁業對海鳥的影響進行評估，分析2004 至2008 年太平洋台灣鮪延繩釣漁船之觀察員資料，由觀察員紀錄之漁業作業項目中，與海鳥可能相關之變項，以相關檢定辨別變數間無共線性存在，再利用逐步迴(stepwise)程序選取模型的最佳組合，以此做為模型分析之候選參數，以泛線性模式 (Generalized linear model, GLM) 及泛加法模式 (Generalized additive model, GAM) 檢視延繩釣漁船對海鳥混獲之影響並透過Akaike information criterion (AIC) 之統計值篩選模型之最適模式。觀察員資料總計有56 航次，總觀察天數為3,973 天，總鉤數為10,192 千鉤，海鳥總混獲隻數為380隻，海鳥總目擊隻數為11,113 隻，海鳥混獲率 (bycatch per unit effort, BPUE) 最大值每千鉤為2.49 隻，最小值每千鉤為0 隻。以Poisson 估計之BPUE 均值每千鉤為0.0373，95 % 信賴區間每千鉤為[0.0336,0.0412]。影響模型顯著性的變數分別為: 年、餌料狀態與裝置避鳥繩。最終模式解釋變異GAM 小於GLM，顯示GAM 比GLM 對於解釋海鳥混獲之影響變因更適合。海鳥混獲易發生於未裝置避鳥繩、使用冷凍餌料及目擊隻數高者，因此，本研究建議漁船於高緯區作業的延繩釣漁船應使用解凍餌料、裝置避鳥繩等措施，以減少海鳥混獲之發生。
The impacts of fishing practices on marine biodiversity have drawn attention in recent years. The seabirds can be incidental caught while contending the baits with fishes, and this has caused the decreasing of some seabird populations. Observer data from 2004 to 2008 are used to analyze the interaction between seabirds and Taiwanese longline fisheries in the Pacific Ocean. We chose those possible related variables based on previous research to identify colinearity between factors by correlation analysis test. We also use stepwise regression to choose the best parameters for the model. Applying generalized linear Models(GLM) and generalized additive models (GAM) to find the influencing factors, we then selected the fitted model by Akaike information criterion(AIC). Among those 56 trips with 3,973 observation sets, 10,192 thousand hooks, three hundred and eighty seabirds are bycatch and 11,113 sighted seabirds. The seabirds bycatch rates is varied ranged from
0 to 2.49 per thousand hooks, and the estimated average was 0.0373 per thousand hooks (with 95 % confidence interval = 0.0336/1000 - 0.0412/1000). The significant factors included year, baits condition, tori lines and the number of seabird sighted. The final GAM model is better than GLM because of smaller explained deviance. Seabirds bycatch rates were higher in high latitude, without tori line and using freeze baits during fishing practice. We suggest longline vessels operating in high latitude should use thawed baits and set tori line to reduce seabirds bycatch.
