Trophic interactions between shark species on the western coast of Baja California Sur: Inferences from stable isotopes

Abstract On the west coast of Baja California Sur, the shark species Mustelus henlei, Carcharhinus falciformis, Prionace glauca, Isurus oxyrinchus, and Sphyrna zygaena are of economic importance and coexist in the same ecosystem. However, the trophic role of each species in this ecosystem is poorly understood. Stable isotopes of nitrogen and carbon ( δ 15N, δ 13C) have been used as an indicator of trophic habitat at different time scales, showing the foraging area and trophic position of sharks. The isotopic values in the muscle and blood of five shark species were analyzed on the southwest coast of Baja California Sur. The isotopic values of P. glauca, S. zygaena and C. falciformis indicated a trophic habitat in oceanic areas, which is a characteristic of these species considering that they feed mainly on mesopelagic cephalopods; whereas M. henlei and I. oxyrinchus showed a benthic diet in oceanic waters. The highest trophic position based on muscle and blood results was in S. zygaena, while the lowest trophic position was in the tissue of C. falciformis, probably because this species feeds on a higher proportion of the crustacean Pleuroncodes planipes. Some of these species share prey and forage in the same area.