Feeding Ecology Of Blue Shark Based On Stable Isotope Ratio Of Vertebrae

The application of stable isotopes in the field of ecology has been increasingly widespread since 1960 s. Isotopes can be used to study the source of carbon and energy, recognize animal%s feeding, trophic position and structures, and further reveal the circulation path and complex trophic relationships between the species and organic matter. Feeding ecology of fish is the basis of marine ecosystems and fisheries resources research, involving stomach content analysis, trophic position estimates, nutrition and food habitats overlap analysis, and modeling of food chains and food webs. Stable carbon and nitrogen isotope, rather than stomach content, can carry and transmit trophic information for a long time. In recent years, stable isotope analysis has become the main method of feeding ecology. This thesis selects the representive species of tuna longline fisheries bycatch!!blue shark(Prionace glauca) to analyze its feeding ecology and trophic information. The main findings are as follows:First, for the samples from eastern Pacific, the range of "13C was-15.76 # ~-13.41 #, with the maximum difference of 2.35 #; the range of " 15 N was 10.62 # ~ 17.72 #, with the maximum difference of 7.1 #. The "13C values and " 15 N values changed with the length of individual, but not obviously. The difference in isotope ratio between the male and female was not significant. The different baseline species had impacts on calculating trophic position. The result shows that using vertebrae to obtain diet characteristic of blue shark is feasible.Second, stable isotope ratio and trophic position were calculated using samples from vertebral origin, middle part, and outer edge, respectively. The results showed that, in the Pacific Ocean, "13C value, "15N value, and trophic position ranges were-16.64 ~-13.08 #, 9.29 ~ 22.37 #, and 2.73 ~ 5.73. All of the "13C, "15N, and trophic position were not significantly different between origin and middle, middle and outer edge, and origin and outer edge(K-S test, P > 0.01). However, for the origin versus outer edge of vertebrae from Atlantic Ocean, and the origin and middle versus outer edge of vertebrae from Indian Ocean, there were significant differences in "13C values. The result shows that feeding habits in different growth stages of blue shark in the two oceans may differ.Third, for the "13C, the calculated values from the Pacific, Atlantic, and Indian Oceans were similar, with less degree of deviation. There was no significant difference between Pacific and Indian Oceans(P=0.592>0.05). And the result of statistical test shows that there was no significant difference between sexes(P=0.638>0.01).The implication of this study is that exploring the oceanic fish trophic position can refer to a baseline of adjacent waters. However, the impact of selection of baseline species should be investigated. In addition, it might be practical to choose any part of vertebrae for obtaining sample of isotope analysis. Further study is needed to intensively test this hypothesis. Blue shark, as highly migratory and top-predator species, may have no significant difference in the diet habits from the three oceans. In the future, more sampling for juvenile fish is needed, which can help explore the whole life cycle of trophic position using stable isotope analysis.