北大西洋長鰭鮪資源評估

Abstract

長鰭鮪, Thunnus alalunga (Bonaterre, 1788),是三大洋重要漁業資源，北大西洋長鰭鮪主要漁業國家包括西班牙、法國、日本與台灣，以表層漁具如竿釣、曳繩釣、中層拖網與刺網為主要漁法，其次為鮪延繩釣。本研究利用不同的資源評估方法，針對北大西洋長鰭鮪資源現況與漁獲壓力，提供資源保育與漁業管理之科學性建議。分別利用泛線性模式(generalized linear model, GLM)以及delta方法，北大西洋台灣鮪延繩釣長鰭鮪漁業資料予以標準化，結果顯示年與漁區效應為最重要標準化因子，且GLM分析結果較佳。所提供台灣鮪釣長鰭鮪標準化CPUE，可反映此資源變化趨勢。CPUE在1970年之前快速下降，1970年代至1980年代後期維持相對穩定度，之後呈現緩慢下降趨勢，2003年迄今(2011)的CPUE則略有上升。漁獲曲線分析估計北大西洋長鰭鮪全死亡率為0.60 yr-1。目前的漁獲死亡率(FCUR)為0.30 yr-1。單位加入生產量分析顯示最適初捕年齡為2歲。單位加入產卵親魚量分析顯示，FCUR接近限制參考點FSSB25％ (0.31 yr-1)，但高於目標參考點FSSB40 (0.20 yr-1)，建議漁獲努力量應減少33%。以非平衡生產量模式(ASPIC)評估北大西洋長鰭鮪資源現況，估計最大可持續生產量(maximum sustainable yield, MSY)為37,210公噸，目前相對生物量B2012/BMSY = 0.68，相對漁獲死亡率F2011/FMSY = 0.82，顯示此資源處於已過漁(overfished)，但無過漁中(overfishing)，投射分析結果建議總容許漁獲量(total allowable catch, TAC)應減少至20,000公噸，可使此資源在10年後回復至MSY水準。本研究評估結果建議，北大西洋長鰭鮪應進行漁獲量管制(output control)，並配合減少漁獲努力量(input control)，以永續利用此漁業資源。

Albacore, Thunnus alalunga (Bonaterre, 1788), support important commercial fisheries globally. In the North Atlantic Ocean, many countries including Spain, France, Japan, and Taiwan fish for albacore with surface gears, including trolls, baitboats, trawls, and gillnets, and with longlines. In this study, the status of the North Atlantic albacore stock was assessed, as well as the level of fishing pressure to which it is subjected, in order to provide scientific suggestions for fisheries management and conservation. Catch and effort data for albacore from the Taiwanese tuna longline fishery in the North Atlantic Ocean were standardized using generalized linear models (GLMs) and the delta approach. Year and area were the most important factors in the model. The standardized CPUE time series from the GLM represents the best available results to reflect the abundance trend of the albacore stock in the North Atlantic Ocean. With a drop before 1970, the standardized CPUE from GLM was relatively stable during the 1970s to the late 1980s, but generally decreased thereafter and increased slightly from 2003 until present. The total mortality rate of the North Atlantic albacore was estimated by catch curve analysis at 0.60 yr-1; the current fishing mortality (FCUR) was estimated at 0.30 yr-1. Per recruit analyses indicated that the optimal age at first capture was 2 yr and the limit reference point FSSB25 was 0.31 yr-1. FCUR higher than the target reference point FSSB40 (0.20 yr-1) suggested that a reduction of 33% in current fishing effort might be appropriate. Stock assessment using a production model (ASPIC) estimated a maximum sustainable yield (MSY) of 37,210 tons, and B2012/BMSY and F2011/FMSY of 0.68 and 0.82 respectively, indicating that this stock was overfished but not subject to overfishing. Projection analysis suggested a reduction of total allowable catch (TAC) to 20,000 tons for the North Atlantic albacore stock to recover to MSY level in 10 years. Based on the assessment results of this study, a TAC regulation (output control) with a reduction of fishing effort (input control) is suggested for sustainable use of North Atlantic albacore.