Combined Gut-Content and Stable Isotope Trophic Analysis of the Pelagic Stingray (Pteroplaytrygon violacea) from the Western North Atlantic Ocean

The understanding of an organism's trophic level is vital to understanding the impact that a specific organism has on the ecosystem, and trophic relationships are vital for correctly modeling ecosystems and ecosystem effects of fisheries removals. The pelagic stingray is found in sub-tropical and tropical waters worldwide and is thought to inhabit the epipelagic zone of the ocean based on fishery catch records. The species is a common bycatch in the Atlantic pelagic longline fishery, yet its ecological role is poorly understood. Very few studies have been done on the diets of the pelagic stingray, most with low sample sizes. For this work, 124 specimens (63 males and 61 females) were collected during commercial pelagic longline fishing operations in the U.S. South Atlantic Bight between August 2008 and December 2009. Stomachs were fixed in formalin, then dissected and the contents quantified to the lowest taxonomic level. Preliminary dissections have shown the major dietary items are crustaceans (40%) and mollusks (30%), in contrast to previous studies from the Pacific, which found mollusks (50%) to be the dominant prey item, followed by Actinopterygiian fishes (19%) and crustaceans (17%). Due to the span of collection time, diet distributions between seasons, between sexes, and length were addressed. Comparisons have shown little differences between diets of males and females or diets between seasons. In addition, stable isotope analysis of δ13C and δ15N was performed on white muscle and liver tissues to correlate trophic feeding level data from the gut-content analysis.