印度洋黃鰭鮪之體長別單位加入生產量和單位加入產卵群生物量評估分析

Abstract

黃鰭鮪（Thunnus albacares）廣泛分布在全球熱帶和亞熱帶海域，是大洋洄游性魚類。黃鰭鮪是鮪類漁業的主要漁獲種類。根據印度洋鮪類委員會（Indian Ocean Tuna Commission，IOTC）資源評估結果顯示印度洋黃鰭鮪的資源量可能已經過度開發。 資源評估所用的資料來源通常是商業性漁獲的資料，有時資料會有不確定性。本研究只利用直接量測的黃鰭鮪體長資料並不參考其他漁業資訊，分析印度洋黃鰭鮪的單位加入生產量和單位加入產卵群生物量，以評估當時的漁業和資源利用情況，並和其他商業性漁獲的資料所估計的結果作比較，以了解此資料和商業性漁獲的資料的差異。樣本船資料為2006年和2007年兩年在印度洋的台灣延繩釣漁船上測量獲得，商業性漁獲資料為中華民國對外漁業合作發展協會提供。利用 Kaymaram(2000)研究發表的成長方程式代入估計其他參數和模式中。利用體長頻度資料轉換漁獲曲線估計之全死亡率為1.98(/年)至2.64(/年)，Cubillos(2003)的估計式估計之自然死亡率為0.75(/年)，漁獲死亡率為1.21(/年)至1.89(/年)，估算選擇率繪製logistic曲線圖，而t50%為1.83至2.19(歲)。將目前初捕年齡設為0.68(歲)，繪製單位加入生產量曲線圖發現2006年和2007年的漁獲死亡率都超過了Fmax和F0.1，而生殖潛能比例在這兩年也都低於20%，表示同時有成長型和加入型過漁的現象，在未來需要降低漁獲死亡率並持續監控印度洋黃鰭鮪的資源利用情形，以達永續發展的目標。根據資料的觀察和參數的估計上都可發現對外漁協的體長資料其體長分布有偏高的趨勢，使得一些參數的估計上可能就有誤差，所以在未來資源評估能像本研究一樣取得測量記錄較有代表性的資料能得到較好的結果。

Thunnus albacares known as yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide. There are important yellowfin tuna fisheries throughout tropical and subtropical seas. The main source of information for some stock assessments are from commercial fisheries data, but the data may have some uncertainties. In this study we have unsampled and direct measurement of length data. We use this data to evaluate the stock status by yield and spawning stock biomass per recruit analyses. And compare the difference between this data and commercial catches data. The growth parameters of Kaymaram(2000) were used for estimation of mortalities and per recruit analyses. The total mortalities ( Z ) were estimated as 1.98-2.64(/year) by the length-converted catch curves. The natural mortalities ( M ) were estimated as 0.75(/year) with the Cubillos’s(2003) equation. The fishing mortalities ( F ) were estimated as 1.21-1.89(/year). t50% was estimated as 1.83-2.19. Given tc as 0.68, according to the yield per recruit curves, the current fishing mortality was beyond F0.1 and Fmax , and spawning potential ratio was about 1%-3.4% suggesting that both growth and recruitment overfishing occurred in this stock. Therefore, the management policy should decrease fishing effort in order to keep the level of sustainable fisheries resource. According to data and parameter estimation can find that Overseas Fisheries Development Council’s length data has high trend of the distribution. So estimation of some parameters, such as mortality and selectivity, there may be some errors.