Foraging habits of dolphinfish and yellowfin tuna in the northwest Atlantic

The New England coastal shelf, a historical seasonal feeding ground for pelagic predators such as yellowfin tuna (Thunnus albacares), has shown an exponential increase in landings of dolphinfish (Coryphaena hippurus) over recent decades. This suggests that dolphinfish may be expanding their distribution pole ward, and have the potential to compete for regional prey resources. The aim of the present study is to conduct a mass-based quantification of the diet habits of large pelagic predators in the northwest Atlantic. Sampling conducted at recreational fishing tournaments from New Jersey to Massachusetts during 2007-2009 has yielded a total of 97 dolphinfish and 65 yellowfin tuna stomachs. Initial analyses of stomach contents have determined that yellowfin consumed cephalopods (37%), fish (38%) and crustaceans (22%) in nearly equal amounts, while dolphinfish diets concentrated primarily on squid (69%). Prey species targeted by both predators included bluefish, shortfin squid and amphipods. A fourth sampling season is planned for 2010 and efforts will be expanded to include fish caught from charter boats and local anglers. Results will describe predator feeding habits and provide an analysis of dietary overlap using the Schoener index. This project will provide necessary information on trophic ecology of these species in the northwest Atlantic.