Diet and trophic level of scalloped hammerhead shark (Sphyrna lewini) from the Gulf of California and Gulf of Tehuantepec, Mexico

We examined the diet and trophic level of Sphyrna lewini in the Gulf of California (GC) during 2001 and in the Gulf of Tehuantepec (GT) during 2005 using data from stomach content and stable isotope analysis of delta N-15 and delta C-13. S. lewini diet was represented by pelagic and benthic prey species where the most important in weight was Scomber japonicus (27.70 +/- 4.54%) in GC, while in GT it was Auxis spp. (26.19 +/- 4.14%). There were differences for delta N-15 and delta C-13 between group sizes, showing a difference in the use of area and resources, while the differences for delta N-15 and delta C-13 between areas were related to changes in the isotopic signal from the base of the food web in each region. Based on delta C-13 and delta N-15 variability, diversity values (GC=3.69; GT=3.17) and diet breadth (GC=0.006; GT=0.002), 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.