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標題: | 利用耳石的年齡標記和元素組成研究南方黑鮪的生活史與洄游環境 Life history and migratory environment of southern bluefin tuna (Thunnus maccoyii) as revealed by age mark and elemental composition in otoliths |
作者: | Yu-Ting Lin 林育廷 |
指導教授: | 曾萬年 |
關鍵字: | 南方黑鮪,耳石,元素組成,洄游環境史,湧昇流,年齡,性別,成長速率, Southern bluefin tuna,otolith,elemental composition,migratory environmental history,upwelling,age,sex,growth rate, |
出版年 : | 2013 |
學位: | 博士 |
摘要: | 南方黑鮪 (Southern bluefin tuna, Thunnus maccoyii)是一種生活史長的大型遠洋洄游性魚類,其生命周期約四十歲,孵化後ㄧ歲至四歲的幼魚會在夏季聚集於澳洲大灣。南方黑鮪族群已被認為過度開發,因此瞭解其洄游生活環境史對於該漁業管理與永續利用是相當重要的。 本研究以耳石為材料,採集來自2003年6-8月與2004年6-8月間於中印度洋攝餌場 (CIO, 29-33°S, 67-91°E)的南方黑鮪耳石418對,同時也採集2005年1-2月在印尼爪哇島附近的產卵場海域 (10-20°S, 110-120°E)的南方黑鮪耳石197對。除了耳石年齡判讀外,另使用雷射光分析系統感應偶合電漿質譜儀測其耳石微量元素組成,比較不同採樣地點與發育階段之差異。耳石中鈉鈣比、鎂鈣比與錳鈣比結果顯示在幼魚階段明顯高於成熟階段,且在耳石第一個轉折點時達到高峰,其後則往下降。耳石第一轉折點恰為南方黑鮪仔稚魚發育成幼魚之階段,發現不同發育階段對於外界水體元素吸收速率有所差異,而耳石邊緣的元素組成亦反映了不同採樣地點的空間差異。澳洲大灣是全世界最大的冷水碳酸鹽沈積海域,同時也是具豐富生產力的湧昇流區域。鋇元素也僅在大洋中的湧昇流區域會出現較高的濃度,因此我們使用南方黑鮪耳石上鋇鈣比作為偵測季節性洄游的重要工具,發現南方黑鮪耳石鋇鈣比在一至四歲的夏季輪出現升高的現象,並與澳洲大灣夏季的湧昇流發生時間一致,在產卵場所採樣之成魚耳石皆在一到四歲間出現鋇鈣比升高現象,但中印度洋的幼魚耳石確有少數樣本沒有鋇鈣比升高的現象,推測可能為不會貢獻於未來產卵族群的少數迷失群。另一方面,兩個不同採樣地點的南方黑鮪耳石核心的元素組成有很高的相似性。證明了南方黑鮪是源自相同產卵場。
魚類成長的性別二形性是魚類生活史上獨特的策略,為了暸解南方黑鮪是否也有此現象出現,本研究分析南方黑鮪耳石共615對耳石判別其年齡,並使用von Bertalanffy成長方程式推算其成長曲線,以ARSS法比較雌雄在成長上差異,結果發現南方黑鮪年齡成長在不同的棲地上亦有所差異,取樣自爪哇島附近產卵場南方黑鮪皆是生殖腺成熟的產卵群,年齡與體型明顯大於中印度洋的南方黑鮪 (all P values < 0.01)。雌魚在成長初期成長較快,但極限體長較小(K=0.109 year -1, L∞=192.38 cm and t0=-1.753 years)。雄魚初期雖成長雖較慢,但極限體長卻較雌魚大(K=0.093 year -1, L∞=211.66 cm and t0=-1.602 years)。在初次性成熟的年齡約為十歲附近且雌雄尚無明顯差異(P = 0.094),但雄魚的體型在性成熟後則是明顯大於雌魚。這也指出性成熟會造成雌雄體型上的差異。南方黑鮪成長的性別二形性則可能是用於成長與生殖能量分配不同所導致。 The southern bluefin tuna (SBT, Thunnus maccoyii) is a long-lived, large, and highly migratory marine fish in the Indian Ocean. They can live up to 40 years and migrate to the Great Australian Bight in the summer when 1-4 years old. The SBT stock is believed to be overexploited. Consequently, it is important to understand its life history and migratory environment to ensure proper fishery management and sustainable exploitation. Otoliths (n=418) of SBT were collected from the feeding ground in the central Indian Ocean (CIO, 29-33°S, 67-91°E) from June to August in 2003 and 2004 (n=197) and from their spawning ground in the adjacent waters of Java, Indonesia (10-20°S, 110-120°E) from January to February 2005. After determined the age by reading age mark, element composition (Na, Mg, Mn, Ca, Sr and Ba), as measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS), and difference among sampling locations and developmental stages. Otolith Na, Mg, and Mn to Ca concentration ratios were significantly higher at the larval stage than at the adult stage. The ratio reached a peak at the first inflection point of the otolith and decreased sharply to a low level thereafter. The temporal change of the element:Ca ratios at the first inflection point corresponded to the life stage transition from larva to juvenile, indicating that the uptake rate of elements from ambient waters was significantly influenced by the ontogenetic change in the fish. The elemental composition at the otolith edge differed significantly between sub-adults on the feeding grounds and adults on the spawning ground. The Great Australian Bight is characterized as the most productive coastal upwelling zone in southern Australia and is the largest area of cool-water carbonate sedimentation in the world. The barium (Ba) level is poor in the open ocean but rich in the upwelling area. The otolith Ba:Ca ratio was used as a natural tag to confirm that SBT seasonally occupy the upwelling area. Otolith Ba:Ca ratios were significantly elevated in the summer growth zone, which corresponds to the upwelling zone when juvenile tuna enter the Great Australian Bight at the age of 1-4 years old. Although almost all of the mature SBT collected in the spawning ground had previously migrated to the Great Australian Bight upwelling area as juveniles, some fish collected from the Central Indian Ocean (CIO) didn’t migrate to the Great Australian Bight upwelling area, perhaps because they are a vagrant population and may contribute less to the spawning stock. On the other hand, the elemental composition of the otolith core of the adult was similar between feeding and spawning grounds, indicating that the SBT in the Indian Ocean had the same larval origin, which is consistent with the single spawning population hypothesis. Sexual dimorphism in growth rate is a unique life history strategy of fishes in the evolution of sex selection. To examine whether this phenomenon exists in SBT, the ages of 615 fish were determined by otolith annuli. The growth curves of SBTs were fitted by the von Bertalanffy growth equation and the growth rate between sexes were compared by the ARSS method. The age and size composition of SBT differed among habitats. The fish collected from Java were all sexually mature spawners and significantly larger and older (170.24± 9.52 cm in mean (± SD) fork length and 16.51± 2.98 years old) than those from CIO (120.07± 17.44 cm and 5.83± 2.36 years old) (all P values < 0.01). The females grew faster but reached a smaller asymptotic length (K= 0.109 year -1, L∞ = 192.38 cm and t0= -1.753 years) than did males (K= 0.093 year -1, L∞ = 211.66 cm and t0= -1.602 years). The mean age of SBT at first maturity (10 years) did not differ significantly between sexes (P = 0.094). Males were significantly larger than females after sexual maturation. The sexual dimorphism in growth rate of southern blue fin tuna was probably due to trade-offs in energy allocation between growth and reproduction. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17290 |
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