Feeding Ecology of the Sandbar Shark (Carcharhinus plumbeus) in South Carolina Estuaries Using delta 13C and delta15N Stable Isotope Analysis
Shiffman, David Samuel
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Shark populations worldwide have greatly declined since the 1970s, and an ecosystem-based fisheries management plan would improve how U.S. shark species are managed. This study utilized stable isotope ratios of carbon and nitrogen (delta13C and delta15N) to examine the feeding ecology of a heavily exploited shark species, the sandbar shark Carcharhinus plumbeus. Data from this study can be used for a future ecosystem-based fishery management plan. Two hundred and sixty two sandbar sharks were sampled in five South Carolina estuaries. There were no significant differences in delta13C or delta 15N between estuaries, years or between male and female sharks, indicating that diet does not change between years, estuaries, or sexes. There were significant differences in delta13C (F=62.9, P=<0.0001) and delta 15N (F= 6.43, P=0.012) signatures between young-of-year (YOY) and juvenile sharks, indicating that South Carolina's sandbar sharks have an ontogenetic diet shift similar to a shift described in Virginia and Hawaii populations. Juvenile sandbar sharks in South Carolina have a wider diet breadth than YOY sharks, which is a common pattern found in elasmobranchs. This study demonstrates that non-lethal sampling methods can obtain the kind of data needed for fisheries managers.