| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 105 === Scalloped hammerhead (Sphyrna lewini), and smooth hammerhead shark (S. zygaena) are the top predators in the marine ecosystem. These two species have been listed on the Appendix Ⅱ and their stockstatus is of great concern by environmental groups. After in order to provide detail data to the ecosystem management in the future, this study use stomach composition analysis and stable isotope analysis to compare the diet between scalloped hammerhead (n= 474) and smooth hammerhead shark (n= 163), from Oct. 2009 to Jan. 2011 and Sep. 2015 to Nov. 2016. The result of stomach composition analysis showed that the main prey items of scalloped hammerhead shark were Scombridae (IRI%= 41.73%), Cepgalopoda (IRI%= 33.46%) and Carangidae (IRI%= 8.19%), stomach empty rate was 67.93%. For smooth hammerhead shark, Cepgalopoda (IRI%= 32.69%), Coryphaena hippurus (IRI%= 31.65%) and Lepidocybium flavobrunneum (IRI%= 14.84%) were the main prey items, stomach empty rate was 48.47%.The stable isotope analysis indicated that δ13C ranged from -18.03 to -15.75‰ with a mean of -16.57± 0.439‰, and δ15N ranged from 11.65 to 14.28‰ with a mean of 13.17± 0.594‰ for scalloped hammerhead shark. For smooth hammerhead shark, δ13C ranged from -17.48 to -16.23‰ with a mean of -16.82± 0.257‰, and δ15N ranged from 11.29 to 14.05‰ with a mean of 13.01± 0.573‰. The Pair-wise comparison was applies for different size classes, the dietary compositions was significantly different for scalloped hammerhead shark. The dietary compositions were significantly different between sexes for smooth hammerhead shark. The dietary comparsitions were significantly different between seasons for two shark species (scalloped hammerhead shark: spring/winter; smooth hammerhead shark: spring/autumn, autumn/winter). Stable isotope analysis by using SPSS statistical software. The δ15N value were significantly different between small size and large size for scalloped hammerhead shark. The δ15N and δ13C values were not significantly different between sexes for two shark species. The δ15N value weres significantly different among seasons the scalloped hammerhead shark: spring/autumn, autumn/winter; smooth hammerhead shark: spring/summer, summer/winter.
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