利用穩定同位素分析探討臺灣東部海域旗魚之食物階層動態

Abstract

本研究利用穩定同位素分析探討臺灣東部海域旗魚類的食物階層動態，自2012年1月至2013年1月止於臺東縣新港魚市場採得黑皮旗魚(n = 216)、劍旗魚(n = 72)、白皮旗魚(n = 43)與紅肉旗魚(n = 14)肌肉樣本，並採獲2012年8月於帛琉海域作業所漁獲之黑皮旗魚(n =37)肌肉樣本。研究結果顯示，臺灣東部海域白皮旗魚與劍旗魚δ15N值最高，黑皮旗魚次之，紅肉旗魚δ15N值最低；白皮旗魚與黑皮旗魚δ13C值最高，劍旗魚與紅肉旗魚次之。δ15N值同時受到體型大小與攝食能力的影響，δ13C值的差異則顯示出不同旗魚覓食的餌料生物組成以及對碳元素不同的利用程度。本研究並收集環境餌料生物進行穩定同位素分析，結果顯示旗魚類與餌料生物δ15N值有0.71 ~ 3.03‰的差距，在一些旗魚魚體中δ15N值與餌料生物可以達到一個營養位階的差距，顯示採集之餌料生物為臺灣東部海域旗魚重要的餌料生物組成之一。黑皮旗魚δ15N值在不同季節間有顯著差異，秋季δ15N值最高，夏季次之，春季與冬季最低；δ13C值在不同季節間則沒有顯著差異，由於δ13C值受到基礎生產力的影響，臺灣東部海域基礎生產力於秋季最高，春季次之，但是黑皮旗魚δ13C值在不同季節間未具顯著差異，推測在黑皮旗魚移動的海域中含有不同海域的穩定同位素資料，長距離的移動將不同海域的情況混合記錄在肌肉組織內。本研究臺灣東部海域黑皮旗魚δ15N值有隨體長增加而上升的趨勢，但是關係並不顯著，帛琉海域黑皮旗魚δ15N值與體長則未有顯著關係，這種情況經常出現在大陸沿岸以及大洋洄游性魚類覓食的海域中，因為掠食者之間餌料生物的組成相差不大，因此顯現穩定同位素相似。在空間分布上帛琉海域黑皮旗魚δ15N值較臺灣東部海域黑皮旗魚要來得高，但δ13C值則未有顯著差異，顯示黑皮旗魚於不同海域可能覓食不同食物階層之餌料生物。

Nitrogen and carbon stable isotopes were used to study the trophic dynamics of the billfishes and prey species in the waters off eastern Taiwan, and of the blue marlin in the Palau waters. White muscle samples were taken and frozen instantly at the Shinkang fish market of eastern Taiwan for the blue marlin, swordfish, black marlin and striped marlin captured in eastern Taiwan waters and the blue marlin captured in Paulau waters. Significant difference in δ15N was found among billfishes in the eastern Taiwan waters.The black marlin and swordfish have the highest δ15N, followed by the blue marlin, and the striped marlin has the lowest δ15N. The black marlin and blue marlin have the highestδ13C, followed by the swordfish and striped marlin.δ15N are influenced by body sizes and the foraging ability, while δ13C differences indicate the feeding ecology of different billfishes and their diverse uses of carbon. The δ15N difference between prey species and billfishes up to one trophic level indicates that the prey species collected in the study might be the important source of prey for billfishes in the eastern Taiwan waters. There was a significant difference in δ15N among seasons, the highest in the fall, followed by the summer, and the lowest in the spring and winter. However, no relationship was found between δ13C and seasons. The δ13C values were influenced by the primary productivity of the ocean. The highest primary productivity of the eastern Taiwan waters occurred in the fall, followed by the spring. The results indicated there are differences in the primary productivityamong seasons. However, no relationship was found in the δ13C among seasons. When the blue marlin moved between different oceans, they combined different stable isotope conditions. The long-distance movement of the blue marlin recorded a mixture of stable isotopes in the muscle tissues among different oceans. The δ15N of billfishes slightly increased with increasing size in the eastern Taiwan waters. However, no relationship was found betweenδ15N and body sizes in the Palau waters.This situation often occurs in the coastal and oceanic waters where migratory fishes feed. Because the prey composition of the ocean are similar, the stable isotope among predators have little difference. The δ15N of blue marlin in thePalau waters was higher than that in the eastern Taiwan waters. However, no difference was found in δ13C between thePalau waters and the eastern Taiwan waters. The stable isotope values in different oceans indicate different productivity, and in the study, the stable isotope values of top predators reveal the different primary productivity in different oceans.