Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

David Kerstetter

Second Advisor

Amy Hirons

Third Advisor

Matt Ajemian


Describing trophic ecology of top predators in marine ecosystems is key to understanding the dynamics of these environments. Feeding ecologies of large predatory fishes were assessed using a combination of stomach content and stable isotope analysis. The target species for this study inhabit the epipelagic ecosystem of the U.S. South Atlantic Bight in the western North Atlantic Ocean. The studied species included five tuna species, five billfish species, Common Dolphinfish, and Wahoo. The goal of this study was to describe and compare the trophic dynamics of each species. From these data, the trophic complex of the offshore pelagic ecosystem was then compared to that of the previously described nearshore pelagic trophic complex. Stomach content analysis found that teleost and cephalopods were the dominant or most common prey type for the studied species. Schoener’s Diet Overlap Indices found a high diet overlap amongst all five tuna species, Wahoo, Common Dolphinfish, Sailfish and Swordfish. Stable isotope analysis found that there are two trophic levels present. Bluefin Tuna are occupying a unique isotopic niche, feeding at the highest trophic position. Stable isotope results also displayed that Bigeye Tuna, Yellowfin Tuna, and Swordfish are feeding on similar depleted carbon sources, potentially due to their unique vertical migrations. The results of this study indicate that the trophic interactions occurring offshore reflect previous findings based on the nearshore trophic complexes. The data from this study contributes to the feeding ecology and trophic understanding of these pelagic species and can be used in ecosystem-based fishery management efforts.



Available for download on Tuesday, September 12, 2023