Heavy Metal Food Chain: Relating Diet and Mercury Bioaccumulation of Top Pelagic Predators in the Northwest Atlantic

Top pelagic predators play a major ecological role in the Northwest Atlantic ecosystem. This status as upper trophic level fishes puts them at greater risk for both harvest and bioaccumulation of toxins. This study seeks to determine the extent and sources of mercury contamination and dietary overlap among five top pelagic predators of the Northwest Atlantic. Study species include yellowfin (Thunnus albacares) and albacore (T. alalunga) tuna, shortfin mako (Isurus oxyrinchus) and common thresher (Alopias vulpinus) sharks, and dolphinfish (Coryphaena hippurus). Important prey identified for both tunas and dolphinfish included Illex illecebrosus, Dactylopterus volitans, amphipods and euphausiids. Mako shark diet consisted almost entirely of Pomatomus saltatrix; thresher diet was more diverse but similarly dominated by teleost prey. An increase in prey size range with predator size was observed in all predators. Yellowfin tuna and dolphinfish exhibited striking similarities in proportional composition by type, but differentiation in prey size when prey species were mutual. Mercury content of predator muscle and important prey will be presented upon completion, describing bioaccumulation trends with predator size and sampling year and estimated biomagnification rates. Understanding and mapping the trophic pathways of mercury through marine food webs is essential for ecosystem-based management of top pelagic predators.