Detecting the Impacts of Commercial Shrimp Trawling on Food Webs in Core Sound, North Carolina

Core Sound, North Carolina, is an inshore estuarine area composed of nursery areas (closed to trawling) as well as waters open to trawling, creating an opportunity to study the ecological network impacts of commercial shrimp trawling.  We used field collections, fisheries data from the NC Trip Ticket program, and Ecopath with Ecosim 6 to create four models of areas Open and Closed to commercial shrimp trawling during the Spring and Fall.  Each model consisted of 65 compartments, ranging from detritus to birds, and four different fisheries (crab pots, gill nets, haul seines, and pound nets).  Two additional gear types, shrimp trawls and skimmer trawls, and an additional compartment (bycatch), were included only in the Open models.  Comparisons of biomass (gC/m²) for common bycatch species (such as pinfish, spot and croaker) indicated greater biomass in areas closed to trawling, and comparisons of infaunal benthic invertebrates, especially polychaetes, indicated greater biomass in areas open to trawling.  Since trawls only operate in the open areas, this suggests a trophic cascade, whereby trawls remove benthic-feeding fishes, releasing their prey (benthic invertebrates) from predation pressure.  Additional comparisons of the models will be presented and will further illustrate ecological network impacts of fishing in Core Sound.