A Multifaceted, Highly Resolved Investigation into the Trophic Role of Small Pelagic Fishes on the Northeast US Continental Shelf

The few species of abundant small pelagic fishes on the Northeast US continental shelf represent critical links between zooplankton production and higher trophic levels. Despite their importance in the overall food web, many of the details and dynamics of the trophic role of forage fishes for this region remain largely unknown. Our ongoing work, focused upon Atlantic Mackerel, Atlantic Herring, Alewife, Blueback Herring, Sand Lance and Butterfish, is taking a multifaceted approach to better understanding the temporal, spatial, and species-specific variability in diets and stable isotope signatures of these ecologically important species. Lab-based, microscopic gut content inspections indicate clear spatial, temporal, and consumer-level differences in diets, as do the consumers’ bulk stable isotope signatures (δ¹³C and δ¹⁵N). Particularly interesting are the high levels of reliance upon appendicularians by Atlantic mackerel and Atlantic herring, as well as the frequent consumption of fish larvae by Atlantic mackerel. In addition to visual inspections and bulk stable isotope analyses, ongoing work includes compound-specific (amino acid) stable isotope analysis to elucidate trophic level and base-of-the-food-web variability, as well as genetics-based prey ID of soft-bodied, morphologically unidentifiable prey frequently present in the guts.