台灣東部海域白皮旗魚生活史參數與生物參考點之估計 及相關未確定性分析

Abstract

本研究利用MULTIFAN多體長頻度分析法分析台灣東部白皮旗魚的體長資料，估計其年齡、成長、死亡率、單位加入量及生物參考點，並於單位加入量分析中將未確定性因子列入考量，以提供該魚種資源評估之參考。自2004年7月至2007年5月間於台東成功新港魚市場共量測5,160尾白皮旗魚體長資料，其中雄魚731尾，雌魚4,225尾，性別不明的204尾。由於雄性白皮旗魚量測的樣本資料不足，且每月之體長資料分布不均，不符合MULTIFAN之基本假設，故雄性白皮旗魚不列入本篇研究之範疇。 雌性白皮旗魚經不同假設之分析，在最小年齡群加入月份為9月，體長樣本數為12 (依月份併合成一年)，以及體長頻度區間為5公分之假設下獲得最佳套適，共分離出12個年齡群，各年齡的平均體長為：L1 = 114.98 cm、L2 = 138.66 cm、L3 = 160.30 cm、L4 = 180.08 cm、L5 = 198.16 cm、L6 = 214.68 cm、L7 = 229.77 cm、L8 = 243.57 cm、L9 = 256.19 cm、L10 = 267.71 cm、L11 = 278.25 cm、L12 = 287.87 cm，其中以第六年齡群為優勢年齡群。von Bertalanffy成長參數為: 成長係數K = 0.090 yr-1，極限體長L∞ = 390.1 cm，體長為零時的理論年齡t0 = - 2.88 yr。估計最大壽命(tmax)為30.41歲，全死亡率為0.55與0.57 yr-1，自然死亡率為0.17與0.20 yr-1，漁獲死亡率為0.35 - 0.40 yr-1，開發率為0.27 - 0.30。在單位加入生產量分析中，最適初捕年齡為6歲，目前漁獲死亡率(FCUR=0.37 yr-1)已超過目標參考點F0.1 (0.31 yr-1)，而在單位加入產卵親魚量分析中，FCUR (0.37 yr-1)亦高於目標參考點FSSB40 (0.16 yr-1)與限制參考點FSSB25 (0.28 yr-1)，因此不建議增加漁獲努力量。另外，利用蒙地卡羅模擬(Monte Carlo simulation)，在7組模擬情境(scenario)下求得生物參考點，發現自然死亡率的未確定性是影響F0.1、FSSB40與FSSB25估計的主要因素，處於目前自然死亡率(M=0.19 yr-1)下，FCUR大於目標參考點F0.1與FSSB40之機率大於85%，FCUR大於限制參考點FSSB25之機率約為50%。為使此魚種的資源達永續利用，不宜再增加漁獲努力量，另應持續對該資源進行評估以及嚴密監測漁業的長期發展。

Age, growth, and mortality of black marlin (Makaira indica) in the waters off eastern Taiwan were estimated based on the length data using MULTIFAN, and applied to the per-recruit analyses with uncertainty incorporated into the parameters. Length data of 5,160 black marlin were collected at Shinkang Fish Market of Taitung during July 2004 to May 2007, of which 731 were males, 4,225 were females, and 204 were sex-unknown. Male black marlin were not discussed in this study due to the sample size of length data, which is not enough to analyze. In the search of MULTIFAN, the best fitting results were obtained when Month 1 was September, the number of sample was 12, and the length interval was 5 cm can obtain.

Twelve age-classes were discriminated in Month 1 sample, and the corresponding von Bertalanffy growth parameters are: growth coefficient (K) was 0.090 yr-1, asymptotic length (L∞) was 390.1 cm and age at zero length (t0) was -2.88 yr. The lifespan was 30.41 yr. The estimates were 0.55 and 0.57 yr-1 for total mortality rates (Z), 0.17 and 0.20 yr-1 for natural mortality rates (M), and 0.35 to 0.40 yr-1 for fishing mortality rates (F), with the exploitation rates (E) being 0.27 - 0.30. Based on the yield-per- recruit analyses, the current fishing mortality (FCUR = 0.37 yr-1) exceeded the target reference point (F0.1 = 0.31 yr-1), and the optimal age at first capture (tc) was suggested to be 6 yr. Increasing the fishing effort could produce the maximum yield, but also result in the risk of overexploitation. For the spawning- biomass-per-recruit, FCUR (0.37 yr-1) also exceeded the target reference point (FSSB40 = 0.16 yr-1) and limit reference point (FSSB25 = 0.28 yr-1). The sensitivity analysis suggested that the natural mortality was the most important impact factor on estimating F0.1, FSSB40, and FSSB25. The probability of FCUR exceeded F0.1 and FSSB40, and FSSB25 are more than 85% and about 50% respectively for the currently understanding of natural mortality (mean ± SE). Therefore, the stock condition and developments in the fishery need to be monitored closely for sustainable exploitation of this stock.