Trophic dynamic of billfishes in eastern Taiwan waters inferred from stable isotope analysis

• Main Authors: Yun-Chen Chang, 張芸甄
• Other Authors: 孫志陸
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/96899212312610207535

碩士 === 國立臺灣大學 === 海洋研究所 === 101 === 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.