Effect of improved weighted branch lines on the fish catching rates of longline fisheries in the waters near Taiwan

Several Regional Fisheries Management Organisations' members have adopted measures to reduce the bycatch rates of seabirds in the longline fishing industry. This study introduced an improved longline system that included slidable clip leads, which can be located close to the hooks, and weighted branch lines. This method was easily purchased and implemented by fishing crews, and the results revealed statistically discernible variations in the catch rates for all fish species (except bigeye tuna) between unweighted and weighted (60 g) branch lines. Specifically, the average sink rate and depth of the unweighted branch lines were 0.31 m/s and 63.91 m, respectively, whereas sink rate and depth for the weighted branch lines was calculated at 0.49 m/s and 66.81 m, respectively, for the weighted branch lines. However, lower catch rates of bigeye tuna on the weighted branch lines were observed, which may have been caused by the altered swing amplitude of the branch lines and baits. Adjusting the distance of the clip leads from the hooks, as well as the weight of the clips, may reduce the effects on catch rates, but requires further study to confirm.

關鍵字

weighted branch line ； longline fishery ； catch rate ； slidable clip leads ； seabird bycatch mitigation

並列摘要

現階段已有許多各區域漁業管理組織要求該管轄區內鮪延繩釣漁船在作業時，必須選用至少兩項措施避免延繩釣漁業意外捕獲海鳥。本研究針對臺灣沿近岸小型延繩釣漁船利用支繩加重改良結構進行實驗，使配重塊經由可撓性結構設置於支繩靠近釣鉤處，另改良結構亦可讓船員裝卸時較為簡便。支繩加重忌避措施實施對鮪延繩釣釣獲率影響結果指出，支繩加重（60g）對大部分目標魚種皆有顯著的負相關影響，然而對大目鮪並無顯著的差異。另外未加重支繩下沉速率與下沉深度分別為0.31m／s與63.91m，而加重後支繩則分別為0.49m／s與66.81m。支繩加重後導致釣獲率顯著下降推測可能為加重結構影響支繩與餌料在水中的擺動方式。建議未來研究方向可針對配重塊離釣鉤位置與配置重量進行改良，以降低支繩加重裝置對釣獲率之影響。

並列關鍵字

鮪延繩釣；支繩結構；釣獲率

國際替代計量

Effect of improved weighted branch lines on the fish catching rates of longline fisheries in the waters near Taiwan

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