- 學位論文
中西太平洋大目鮪之豐度指標標準化及資源評估
Standardization of abundance indices and stock assessment for the bigeye tuna Thunnus obesus in the western and central Pacific Ocean
摘要
大目鮪(bigeye tuna, Thunnus obesus)為經濟價值極高的大洋性熱帶鮪類，廣泛分佈於三大洋的熱帶及亞熱帶海域。中西太平洋海域的大目鮪資源相當豐富，為多種漁具包括鮪延繩釣、鰹鮪圍網及鰹竿釣等所開發利用，但主要仍以臺灣、日本及韓國鮪延繩釣漁業之漁獲成魚為主，大多數的幼魚則由其他漁具所漁獲，例如鰹鮪圍網等。其中2007年鮪延繩釣漁業約佔大目鮪總漁獲量之57%；鰹鮪圍網漁業約佔大目鮪總漁獲量之27%。 單位努力漁獲量標準化(Standardized CPUE)是最常被用來反應資源豐度的指標之一，但是單位努力漁獲量容易受到時空、環境因子和漁業策略等因素的影響，在引用到生產量模式進行資源評估之前，需藉由單位努力漁獲量標準化，將各種可能影響單位努力漁獲量的因子排除，以獲得較符合真實狀況的資源量變動趨勢。因此，本研究利用泛線性模式(GLM)進行中西太平洋1975年至2007年臺灣遠洋鮪延繩釣及1975年至2006年日本遠洋鮪延繩釣漁業之大目鮪名目單位努力漁獲量標準化，將名目漁獲努力量(nominal effort)轉換為更效漁獲努力量(effective effort)。 以1975至 2007年中西太平洋大目鮪之日本遠洋鮪釣漁業、臺灣遠洋鮪釣漁業、其他國家鮪釣漁業及其他漁業等四組漁業別的年總漁獲量及年總更效漁獲努力量資料，套適ASPIC非平衡生產量模式(non-equilibrium production model)評估此系群之資源狀態，估計最大持續生產量(MSY)為60,710 公噸、相對漁獲死亡率(F/FMSY)為1.74、相對系群生物量(B/BMSY)為1.342，顯示中西太平洋大目鮪資源已處於過漁(overfishing)狀態，目前漁獲量已經超過MSY最適利用水準的兩倍以上，應持續降低漁獲量或漁獲努力量，且該資源狀況仍應持續加以密切監視與評估。
並列摘要
Bigeye tuna (Thunnus obesus) is an economically important species, widely distri-buted in the tropical and subtropical waters of Atlantic, Indian and Pacific Oceans. High catch is concentrated in the western and central Pacific Ocean (WCPO), which was har-vested by a variety of fishing gears (including tuna longline, purse-seine and pole-and-line). The major fishing countries of the bigeye tuna is Taiwan, Japan and Ko-rea in which the adult was fished by longliners and the juvenile by other gear types (e.g. purse-seine). 57% of the bigeye tuna catch was taken by longliners, and 27% by purse seiners in 2007. Standardized catch-per-unit-effort (CPUE) is the most commonly used as an index to reflect stock abundance. To obtain the actual abundance trend, possible factors in-fluencing the catch rate need to be removed by using standardization, because CPUE may differ across time, space, environment and fishing strategy etc. In this study, the generalized linear models (GLM) were applied to standardize the bigeye tuna catch and effort data of Taiwanese distant-water longline fishery from 1975 to 2007 and of Japa-nese distant-water longline fishery from 1975 to 2006 to convert the nominal efforts to effective efforts. The non-equilibrium production model (ASPIC) was then applied to assess the stock status of the bigeye tuna in WCPO, from 1975 to 2007. The results showed that the maximum sustainable yield (MSY) of the stock was 60,710 MT, F/FMSY was 1.74 and B/BMSY was 1.342. Current catches are more than double the MSY, indicating the bigeye tuna stock is overfishing. It is suggested that catch or fishing effort in WCPO for the bigeye tuna have to decrease continuously, and that stock's condition and develop-ment in the fisheries be monitored very carefully.