以生產量模式評估中西太平洋大目鮪之動態資源

Abstract

大目鮪(bigeye tuna, Thunnus obesus)是一種經濟價值極高的鮪類魚種，主要捕獲漁業為延繩釣。而在中西太平洋海域裡，鮪類漁獲量佔有舉足輕重的地位，大目鮪為其中之一標的魚種。因此近年來對海洋資源的研究越來越重視趨勢下，本篇報告先將台灣中西太平洋鮪延繩釣大目鮪的名目漁獲量(nominal effort)，使用Honma法進行努力量的標準化；再以台灣的中西太平洋延繩釣漁具漁法為中西太平洋各國家的漁具標準，求得統一的有效努力量(effective effort)單位；最後將有效努力量代入生產量模式(production model)：Schaefer model、Fox model、 和Pella-Tomlinson model，以估算中西太平洋漁區的最大永續生產量(maximum sustainable yield, MSY)、及最佳的漁獲努力量(fMSY)。以供漁業當局對漁業管理的決策參考值。 Schaefer model估算結果為：在最佳漁獲努力量為478,218萬鉤時，其最大永續漁獲量為155,380公噸；Fox model估算結果為：在最佳漁獲努力量為525,431萬鉤時，其最大永續漁獲量為129,955公噸；當曲線參數(m, curve parameters)為1.483時的Pella-Tomlinson model，是所有模式裡有最大的相關係數，其最佳漁獲努力量為488,591萬鉤時，其最大永續漁獲量為141,935公噸。 Hampton使用MULTIFAN-CL估計2003中西太平洋的MSY為40,000-80,000公噸，與生產量模式相比，有懸殊的差異。但以近來中西太平洋的總漁獲逐年增加的趨勢(2005年的總漁獲量達157,000公噸)，顯然大目鮪的資源狀況已達過漁狀態。故本報告以Pella-Tomlinson model當m=1.483時有較高的相關係數，為最適合描述中西太平洋大目鮪的資源狀態。

This paper tries to assess the exploitation of bigeye tuna, Thunnus obesus, in the western and centeral Pacific by using catch statistics longline fisheries collected by Overseas Fisheries Development Council of Republic of China and WCPFC (Western and Central Pacific Fisheries Commission). First, the nominal effort was converted to effective effort by Honma method. Then, the effective effort was fitted by production models: Schaefer model, Fox model and Pella-Tomlinson model. At last, based on the results of these models: MSY (maximum sustainable yield) and fMSY were calculated for fishery management as Schaefer model: MSY=155,380 tons; fMSY=478,218 (10,000 hooks), Fox model: MSY=129,955 tons; fMSY=525,431 (10,000 hooks), Pella-Tomlinson model when m=1.483: MSY=141,935 tons; fMSY=488,591 (10,000 hooks), respectively. Compared MSY estimated by production model with MULTIFAN-CL by Hampton, 40,000-80,000 tons in 2003 which was quite lower than that by production model. Recently, the total yield of bigeye tuna in the western and centeral Pacific was increasing. In 2005, the yield reached up to 157,000 tons. If we adopted MSY from MULTIFAN-CL, we supported to use tuna in western and centeral Pacific seems to be overfishing. Pella-Tomlinson model with m=1.483 as the optimum way to regulate the bigeye tuna stock in the western and centeral Pacific.