Quantifying the Contribution of Diadromous Species to the Diets of Marine Predators in the Gulf of Maine

We analyzed data from the National Marine Fisheries Service’s Food Habits database to quantify the importance of diadromous species in the diets of marine predators.  Stomach content data from 1973 – 2010 were included in our analyses.  We quantified the number of stomachs that contained diadromous prey, as well as calculating the percent weight (%W) and frequency of occurrence (%O) that contained these prey types.  Additionally, we estimated predator-prey size ratios to better understand the sources of predation.  Diadromous species were common in 12 species of predators.  Results indicated that Anguiliformes was the most common diadromous prey found in diets followed by members of the shad and river herring complex.  Although predation on diadromous fishes occurred throughout the Northeast Fishery Science Center’s bottom trawl survey’s range from Nova Scotia to Cape Hatteras, diadromous fishes were consumed more frequently and made up a greater percentage of predator diets in Gulf of Maine inshore waters.  Throughout the survey range, striped bass and bluefish diets were composed of a higher %O and %W of diadromous prey than other predator species.  Gulf of Maine (GOM) inshore predation on diadromous fishes was dominated by goosefish, having a maximum contribution of 10% by weight in the southern portion of the GOM. By %O and %W, other notable GOM predators of diadromous fishes included Gadiformes (especially Atlantic cod, white hake, and silver hake) spiny dogfish, and thorny skate.  These results indicate a limited but extant coupling of freshwater production to marine food webs.  As efforts to restore diadromous species in the northeastern US continue, our study may demonstrate how the Gulf of Maine ecosystem will respond to increases in the abundance of diadromous species.