北太平洋長鰭鮪生活史特徵及單位加入生產量分析

Abstract

本論文主要內容為研究北太平洋長鰭鮪(Thunnus alalunga)的生物學(包括年齡、成長及生殖生物學)，並對此系群進行雌雄別單位加入生產量分析，以提供此系群生活史參數及生物參考點。在2001至2008年期間，總共採集到293尾北太平洋長鰭鮪(其中，133尾雌魚，尾叉長46 cm至101 cm；160尾雄魚，尾叉長45 cm至118 cm)，做為生物學研究樣本。耳石邊緣分析的結果驗證扁平石切片上所判讀的年輪是一年形成一輪，年輪形成盛期為9月至翌年2月。以耳石微細構造分析第一年輪形成時的魚齡，結果發現第一年輪形成時，並非魚齡皆已達1歲。本論文的結果建議第一年輪所代表的魚齡約為0.75歲。成長研究的結果指出，雌魚和雄魚具有不同的成長方程式。本論文所估計的von Bertalanffy成長參數如下：雌魚為L∞ = 103.5 cm、K = 0.340 year−1及t0 = −0.53 years；雄魚為L∞ = 114.0 cm、K = 0.253 year−1及t0 = −1.01 years。再者，此系群體長與體重關係式(指數函數)的參數估計值為：a = 2.964×10−5及b = 2.928。此系群達50%性成熟的尾叉長約為85 cm。成熟雄魚比雌魚成長到較大的體型及年齡，而雄魚和雌魚在達到性成熟後，成長速率才有較大的差異。由von Bertalanffy參數所估計的自然死亡率(M, in year−1)值顯示，雌魚的M值比雄魚高。單位加入生產量分析所估計最佳的初捕年齡為2歲(2.5歲魚平均尾叉長約為67 cm)。以雌魚為例，在M = 0.3時，模式一(使用一組漁具選擇率)所估計的參考點F0.1 (year−1)及F25% (year−1)分別為0.32及0.30，而模式二(使用另一組漁具選擇率)所估計的值分別為0.36及0.35。再者，在M = 0.5時，模式一所估計的F0.1及F25%分別為0.55及0.36，而模式二所估計的值分別為0.62及0.43。若此系群的M值大於0.3時，則以F25%做為漁業管理的參考點會比使用F0.1為佳。

This dissertation presents the results of biological investigations (including information on age, growth, and reproductive biology) and sex-specific yield-per-recruit analyses of North Pacific albacore (Thunnus alalunga) to provide life-history parameters and biological reference points for this stock. North Pacific albacore specimens (133 females, 46 to 101 cm in fork length, LF; 160 males, 45 to 118 cm LF) were collected for biological investigations from 2001 to 2008. The results of otolith edge analysis indicate that the sagittal otolith growth zones composed of relatively compact micro-increments represent annual growth marks that are primarily formed during the months of September and February. The age estimates of first annulus formation obtained by examining otolith microstructure suggest that the first annulus represents an age of less than 1 year. This dissertation estimates 0.75 years to be the age represented by the first annulus. The results of fish growth modeling indicate that this stock exhibits sex-specific growth patterns. The estimated von Bertalanffy growth parameters for females were L∞ = 103.5 cm, K = 0.340 year−1, and t0 = −0.53 years; the parameters for males were L∞ = 114.0 cm, K = 0.253 year−1, and t0 = −1.01 years. The length-weight parameters (for a power function) estimated for this stock were a = 2.964×10−5 and b = 2.928. The estimated length at 50% maturity of this stock was 85 cm LF. The results of the biological investigations suggest that males attain to a greater size and age than females and that sexual size dimorphism increases after sexual maturity is reached. The natural mortality (M, in year−1) estimates obtained with von Bertalanffy growth parameters indicate that females tend to have a higher M value than males. The simulated yield-per-recruit values suggest that the optimal age at first capture is approximately 2 years (with an average LF of 67 cm for 2.5-year-old fish). For females, the reference points F0.1 (year−1) and F25% (year−1) estimated at M = 0.3 under Model Scenario 1 (a set of gear selectivity for all age classes) are 0.32 and 0.30, respectively; the values obtained with Model Scenario 2 (another set of gear selectivity) are 0.36 and 0.35, respectively. At M = 0.5, the reference points obtained with Model Scenario 1 are F0.1 = 0.55 and F25% = 0.36, and those obtained with Model Scenario 2 are F0.1 = 0.62 and F25% = 0.43. The reference point F25% is preferable to F0.1 for the fisheries management of this stock if M > 0.3.