Cooperative Fish and Wildlife Research Units Program: South Carolina
Education, Research and Technical Assistance for Managing Our Natural Resources

Population dynamics of seabirds have been linked to availability of bycatch discarded from commercial fishery operations. South Carolina supports a substantial commercial shrimping industry that operates primarily in inshore waters where locally breeding Brown Pelicans (Pelecanus occidentalis), Laughing Gulls (Larus auritus), Royal Terns (Sterna maxima), and Sandwich Terns (Sterna sandvicensis) forage. We examined the relative abundance of these seabirds at shrimp trawlers during the breeding season, measured the consumption fate of fish species collected as bycatch and subsequently discarded, and measured the energy density and proximate composition of these discarded items. Trawlers were attended regularly by all four locally-breeding seabirds out to 30 km from colonies. Laughing Gulls were the most frequently observed followed by brown pelicans, royal terns, and then sandwich terns. Seabirds captured ca. 70% of experimentally discarded items from shrimp tralwers. Brown pelicans consumed more discards than predicted based on their frequency while the other species each consumed fewer discards than predicted based on their frequency. Seabirds selected smaller items compared to larger items, and selected benthic fish that typically would not be available to this suite of seabirds. Energy density of common discards ranged from 2.9 – 4.1 kJ/g wet mass and there appeared to be no difference in the energy density of the pelagic or demersal fish we measured. Our data suggest that all four locally breeding seabirds forage at trawlers frequently enough that changes in the size of the shrimp fleet would have the potential to affect their foraging ecology.