Investigating diet patterns of highly mobile marine predators using stomach contents, stable isotope, and fatty acid analyses

Determining what animals eat is simultaneously challenging and yet also critical for ecologists, fisheries scientists, and resource managers. The tools of trophic ecology have expanded considerably in the last half century in pursuit of this goal. In this study, we combined stomach contents, stable isotope, and fatty acid analyses to investigate trophic patterns in three species of highly mobile, pelagic predators: striped marlin (Kajikia audax), blue marlin (Makaira nigricans), and common dolphinfish (Coryphaena hippurus). We were particularly interested in examining individual diet specialization among these species. We compared the short-term stomach contents with long-term diet proportions estimated from stable isotope ratios and fatty acid profiles using a Bayesian mixing model. Our results indicate that all three species feed on a mix of prey types. This work furthermore suggests that individuals of all three predator species demonstrate generalist feeding habits, with minimal differences in long-term (weeks, months) diet estimates between individuals with different short-term (hours, days) stomach contents. This novel, three-part analytical approach can elucidate complex and otherwise elusive trophic dynamics.