Feeding habits and trophic level of the shovelnose guitarfish (Pseudobatos productus) in the upper Gulf of California

The shovelnose guitarfish (Pseudobatos productus) is the most abundant and economically important batoid in Gulf of California fisheries. Despite the importance of the guitarfish in the demersal ecosystem, its trophic relationships are poorly understood. Results from stomach content and stable isotope analysis indicate P. productus is a specialist predator that feeds on coastal benthic organisms, mainly crustaceans, followed by fishes and cephalopods in the Upper Gulf of California. Males and females did not differ in dietary composition and isotopic values. Pseudobatos productus displayed ontogenetic changes in the diet, with smaller, immature individuals having a more specialized diet and mature individuals becoming generalist predators. Size classes I (< 570 mm) and II (> 570 mm) fed almost exclusively on crustaceans (99.78% and 82.37% IRI, respectively). Size class III (> 832 mm) increased consumption of fishes (22.11% IRI) and squid (6.54% IRI). Ontogenetic diet shifts were strongly supported by the SIAR mixing model. Stomach content and stable isotope analyses classify P. productus as a second-order predator.