Y.E Torres Rojas
F Paez Osuna
J Camalich
F Galvan Magaña

We examined the diet and trophic level of Sphyrna lewini in the Gulf of California (GC) during ۲۰۰۱ and in the Gulf of Tehuantepec (GT) during ۲۰۰۵ using data from stomach content and stable isotope analysis of δ۱۵N and δ۱۳C. S. lewini diet was represented by pelagic and benthic prey species where the most important in weight was Scomber japonicus (۲۷.۷۰±۴.۵۴%) in GC, while in GT it was Auxis spp. (۲۶.۱۹±۴.۱۴%). There were differences for δ۱۵N and δ۱۳C between group sizes, showing a difference in the use of area and resources, while the differences for δ۱۵N and δ۱۳C between areas were related to changes in the isotopic signal from the base of the food web in each region. Based on δ۱۳C and δ۱۵N variability, diversity values (GC=۳.۶۹ GT=۳.۱۷) and diet breadth (GC=۰.۰۰۶ GT=۰.۰۰۲), we propose that S. lewini is an opportunistic predator. The trophic level of S. lewini was above four in all categories, which indicates that S. lewini is a tertiary consumer. We may conclude that S. lewini plays an important functional role as top predator within areas of Mexico.

Shark, Sphyrna lewini, Gulf of Tehuantepec, Mexico, Stomach content analysis, Stable isotopes.