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On the southwest coast of Baja California Sur, Mexico, we record four shark species: Carcharhinus falciformis, Prionace glauca, Isurus oxyrinchus and Sphyrna zygaena, which are sharks of economic and ecologic importance which coexist in the same ecosystem. However the trophic role of each species is poorly known. Stable isotopes of nitrogen and carbon ([Delta]15N, [Delta]13C) are used as indicators of feeding habits on different time scales, allowing to know the foraging areas and trophic position. Also the stable isotope analysis in blood and muscle, will allow to infer trophic level and trophic breadth, and the intraspecific and interspecific interactions in different time life. The stable isotope results showed values in blood for C. falciformis: 15N = 16.65 ± 0.68 ‰, 13C = -17.03 ± 0.25 ‰; I. oxyrinchus: 15N = 18.34 ± 0.61 ‰, 13C = -17.47 ± 0.53 ‰; P. glauca: 15N = 18.17 ± 0.78 ‰, 13C = -17.22 ± 0.83 ‰; S. zygaena: 15N = 19.28 ± 1.14 ‰, 13C = -16.94 ± 0.63 ‰. Whereas in muscle were: C. falciformis: 15N = 16.66 ± 0.69 ‰,13C = -17.03 ± 0.25 ‰; I. oxyrinchus: 15N = 19.41 ± 1.16 ‰,13C = -17.18 ± 0.52 ‰; P. glauca: 15N = 17.83 ± 0.66 ‰,13C = -17.76 ± 0.59 ‰ and S. zygaena: 15N = 19.66 ± 1.10 ‰,13C = -16.68 ± 0.37 ‰. Significant isotopic differences were found between tissues, sex and maturity stages within species, which would indicate interspecific trophic segregation at different time scales.

Palabras clave: stable isotopes; feeding interactions; elasmobranchs.

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