Temporal and Spatial Comparisons of Pelagic Apex Predator Foraging Ecology

We examined diet, dietary niche width, and diet overlap of blue marlins Makaira nigricans, dolphinfish Coryphaena hippurus, yellowfin tuna Thunnus albacares, and wahoos Acanthocybium solandri caught in the western North Atlantic Ocean during the Big Rock Blue Marlin Tournament (BRT) in 1998–2000 and 2003–2009 and dolphinfish captured outside the BRT from 2002 to 2004.  Additionally, we compared trophic data for these species between the early 1980s and 2000s and among North Atlantic, South Atlantic, and North Pacific oceans.  Scombrids were important prey of blue marlins, yellowfin tuna, and wahoos; other frequently consumed prey included cephalopods (for yellowfin tuna and wahoos) and exocoetids (for yellowfin tuna).  Dolphinfish diets included exocoetids, portunids, and conspecifics as important prey.  Blue marlins and wahoos consumed relatively few prey species (i.e., low dietary niche width), while dolphinfish had the highest dietary niche width; yellowfin tuna had intermediate niche width values.  Most interspecific diet overlap values with dolphinfish were not significant; however, blue marlins, yellowfin tuna, and wahoos had significant diet overlap due to their reliance on scombrid prey. Prey types found in blue marlins, dolphinfish, and wahoos were more consistent among BRT years than prey found in yellowfin tuna.  The prey of yellowfin tuna and wahoos collected during BRT years correlated with historic diet data from North Carolina, the Gulf of Mexico, and the Bahamas.  Based on principal components analysis, diets from North Atlantic and North Pacific clustered together for blue marlins, dolphinfish, yellowfin tuna, and wahoos.  Although differences were found, the diets of each predator were largely consistent both temporally (e.g., over the past three decades in the Gulf Stream) and spatially (among oceans), despite potential effects of fishing or environmental change.