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RATIONALE: Individual foraging behavior is an important variable of predators commonly studied at the population
level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context,
stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using
traditional methods.
METHODS: We determined the isotopic composition (?13C and ?15N values) of dorsal muscle and vertebrae of Sphyrna
lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta
Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values.
RESULTS: There were no significant differences in the isotopic values of muscle samples between sexes, but there were
differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche
overlap was observed between S. lewini individual vertebrae. We found differences in the ?15N values of S. zygaena
vertebrae, with lower values in the first group of samples.
CONCLUSIONS: Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap
between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen
isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies
on trophic ecology.

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