Foraging ecology of large pelagic fishes in the US South Atlantic: structured piscivory shapes trophic niche variation

Sustainable management of marine fishery resources requires an understanding of the ecological relationships that contribute to community structure and population dynamics. In offshore marine ecosystems, the functional roles played by many large pelagic predators are poorly understood, yet this knowledge is essential to ecosystem-based management approaches. Here we report on the results of a multiyear (2010–2013) study to evaluate the trophic relationships within a guild of apex predatory fishes in the western Atlantic Ocean. Quantitative diet analyses were completed for wahoo Acanthocybium solandri, dolphinfish Coryphaena hippurus, yellowfin tuna Thunnus albacares, and blackfin tuna T. atlanticus during multiple seasons. Fishes were the most important prey by mass for all predators during all seasons and occurred with high frequency; however, crustacean and molluscan prey were also important dietary components for most of the predators. The diversity of prey eaten was high, with nearly 50 unique families represented; yet, a few prey groups such as scombrid fishes (Auxis spp.), flying fish (exocoetids), and ommastrephid squids, occurred more universally and dominated the diets of some predators during certain seasons. Diet similarity was highest between dolphinfish and blackfin tuna and also between wahoo and yellowfin tuna, but was generally dependent on season and driven by overlap in fish prey. Importantly, the extent of piscivory and specialization on unique fish prey groups supported a structured piscivore guild within this pelagic ecosystem, leading to separation among trophic niches and reduced overlap in prey resources. Our findings provide a temporally (seasonal and inter-annual) extensive evaluation of the trophic relationships among large pelagic fish predators in the US South Atlantic, which should inform an ecosystem-based understanding of community dynamics and fishery impacts.