探討太平洋黑鮪成體年齡結構之時空變化

Spatial and Temporal Analysis of Adult Demographic Structures for the Pacific Bluefin Tuna Thunnus orientalis

陳穎萱(Ying-Shiuan Chen)

指導教授 ： 王慧瑜

國立臺灣大學/理學院/海洋研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01643

摘要

成體年齡結構（adult demographic structure）與魚類族群的繁殖能力有關，因此為重要的族群參數。本研究為了解太平洋黑鮪（Thunnus orientalis）的族群動態，探討其成體年齡結構隨時空的變化，以及成體年平均體長與0歲魚（young-of-the-year）的數量（以曳繩釣之單位努力捕獲量為指標）、幼體和成體階段的漁業死亡率之間的關係。我們分析位於太平洋黑鮪產卵場的三個漁業資料，包含在西北太平洋的台灣延繩釣（Taiwanese longliners, TWL, 1993-2013）、日本沿岸延繩釣（Japanese coastal longliners, JCL, 1994-2009），以及在日本海的圍網漁業（Japanese purse seine, JPS, 1987-2010）。我們發現黑鮪成魚的平均體長在三個漁業之間有顯著差異：TWL > JCL > JPS（分別為219.6、188.1及139.6公分）。另外，TWL和JCL的年平均體長隨時間上升，此上升趨勢與前人研究發現的漁業降低魚種之平均年齡或體長不同。我們以廣義最小平方法模式（Generalized least squares; GLS）分析發現，成體平均體長之時間變化與幼體或成體階段之漁業死亡率有顯著關係，而與0歲魚數量的關係只有在TWL觀察到。本研究顯示幼體或成體階段之漁業死亡率為影響太平洋黑鮪年齡結構之時間變化的潛在因素。我們建議在太平洋黑鮪的資源評估中應考慮其成體年齡結構之時空變化（例如：產卵生物量的估計，spawning stock biomass, SSB）。在漁業管理方面，應該長期監控太平洋黑鮪體長或年齡結構，並深入了解漁業對其族群動態的影響。

關鍵字

成體年齡結構 ； 族群動態 ； 太平洋黑鮪 ； 幼體及成體階段之漁業死亡率 ； 廣義最小平方法模式

並列摘要

Adult demographic structure is a critical parameter determining reproductive potential for the long-lived iteroparous fishes. To enhance understanding of the Pacific bluefin tuna (PBF) population dynamics, we explored spatial and temporal variation in adult size structures (indexed by mean lengths) and evaluated how adult mean lengths varied with young-of-the-year (YOY) abundance (indexed by PBF troll fishery catch-per-unit-effort, CPUE) and average fishing mortality at juvenile and adult stages. From various sources, we compiled adult lengths based on catch data of three fisheries operated on the PBF spawning grounds, i.e., the Taiwanese and Japanese coastal longliners (TWL and JCL, respectively) at the southern spawning ground in the western Pacific and the Japanese purse seine (JPS) fisheries at the northern spawning ground in the Sea of Japan. In addition, we obtained time series of YOY abundance and fishing mortality rates from the stock assessment reports. Adult mean lengths (in cm) varied considerably among the three fisheries: TWL (219.6) > JCL (188.1) > JPS (139.6). Temporally, adult mean lengths increased since mid-1990s for the TWL and JCL but not JPS. Analysis based on generalized least squares regression (GLS) revealed that juvenile and/or adult fishing morality had significant effects on annual mean lengths for these adult fisheries. In addition, the effect of YOY abundance on mean lengths was significant only for the TWL. Our results provide important information to enhance precision of the PBF stock assessment (e.g., estimation of spawning stock biomass, SSB). To achieve effective fisheries management, we suggest continuing conducting long-term monitoring of demographic changes and studying fishing-induced effects on such changes for the PBF.

並列關鍵字

adult demographic structure ； population dynamic ； Pacific bluefin tuna ； YOY ； adult and juvenile fishing mortality

參考文獻

Addis, P., M. Secci, I. Locci, A. Cau, and A. Sabatini. 2012. Analysis of Atlantic bluefin tuna catches from the last Tonnara in the Mediterranean Sea: 1993-2010. Fisheries Research 127–128: 133–141.

Beamish, R. J., G. A. McFarlane, and A. Benson. 2006. Longevity overfishing. Progress in Oceanography 68: 289–302.

Berkeley, S.A., M. A. Hixon, R. J. Larson, and M. S. Love. 2004a. Fisheries sustainability via protection of age structure and spatial distribution of fish populations. Fisheries 29: 23–32.

Berkeley, S.A., C. Chapman, and S. M. Sogard. 2004b. Maternal age as a determinant of larval growth and survival in a marine fish, Sebastes melanops. Ecology 85: 1258–1264.

Bjornstad, O. N., R. M. Nisbet, and J-M. Fromentin. 2004. Trends and cohort resonant effects in age-structured populations. Journal of Animal Ecology 73: 1157–1167.