Resumen del producto

Diet analysis is a fundamental aspect of the management of elasmobranchs and is used to determine interactions between species and their environment. The biochemical analysis of stable isotopes 13C and 15N in tissues allows to quantitatively analyze the assimilated diet and the spatio-temporal trophic habitat. Nursery areas work as refuges for neonate and juvenile sharks, are characterized by a higher abundance of prey and offer protection against predators. The objective of this study was to describe the trophic habitat of the Pacific sharpnose shark and the Munk’s devil ray within their nursery areas in La Paz Bay using the analysis of stable isotopes 13C and 15N in whole blood samples. Isotopic values were compared between sexes, stages, season of year, niche overlap, trophic position, and trophic amplitude. Blood samples were taken from the caudal vein of Pacific sharpnose sharks and from the pectoral fin in Munk’s devil rays. 182 samples were taken from Pacific sharpnose sharks and 57 from Munk’s devil rays all from live specimens caught in the wild. Neonates of both species have enriched isotopic values, due to isotopic fractionation that occurs from the mother to the embryo during pregnancy. In both species, juveniles presented lower values than adults in 13C and 15N, likely because they are feed on organisms with lower trophic positions and in coastal zones. The estimated trophic positions, match for a tertiary carnivorous predator (Pacific Sharpnose shark, PT = 4.4) and a secondary consumer (Munk´s devil ray, PT = 3.29). Pacific Sharpnose sharks showed a greater trophic amplitude, being generalist feeders (Variance= 1.05), unlike Munk’s Devil ray that are more specialized (Variance = 0.32). Pacific Sharpnose shark and devil ray juveniles and neonates are reflecting the same trophic niche role when they are adults. The analysis of stable isotopes using whole blood demonstrates an acceptable and non-lethal technique to use on sensitive stages as well as protected species.

Palabras clave: Rhizoprionodon longurio; Mobula munkiana; nursery areas

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