Combined gut-content and stable isotope trophic analysis of the pelagic stingray Pteroplaytrygon violacea (Bonaparte, 1832) diet from the western North Atlantic Ocean

Abstract

The understanding of trophic relationships is vital for correctly modeling ecosystems and ecosystem effects of fisheries removals. The pelagic stingray is found in epipelagic sub-tropical and tropical waters worldwide and is a common bycatch in pelagic longline fisheries. Between August 2008 and November 2011, 156 specimens (81 males; 75 females) were collected during pelagic longline fishing operations in the US South Atlantic Bight and Gulf of Mexico. Stomach content analyses found that the major prey items were cephalopod molluscs (59.18%), followed by actinopterygiian fishes (37.75%), and decapod crustaceans (35.71%). These concentrations of prey items found in the stomachs coincide with previous studies done in the Pacific Ocean. In contrast to previous studies that found high percentages of empty stomachs (63%), the current percentage of empty stomachs was much lower (25.6%), likely due to shorter times between collection and inspection. Stable isotope analysis (δ13C and δ15N) was performed on white muscle in order to correlate the trophic position with gut-content analysis. The δ13C values ranged from -18.81‰ to -16.70‰, while the δ15N ranged from 6.11‰ to 11.88‰. Modeling of stable isotope data suggest that while squid are occasionally an important part of the pelagic stingray diet, prey usually consist of shrimp and other pelagic crustaceans. Pelagic stingrays fed within two trophic levels, but their prey appeared to feed on different carbon sources than those found in other pelagic elasmobranchs. A deeper understanding of the pelagic stingray diet sources can help fisheries management as it begins to transition into ecosystem-based management.