Seabird Attendance at Shrimp Trawlers in Nearshore Waters of South Carolina

Abstract

Many seabirds attend commercial fishing vessels to obtain food, but the effect on their distribution and abundance has received virtually no attention off the southeastern United States.We examined distribution and abundance of four locally breeding seabirds (Brown Pelicans Pelecanus occidentalis, Laughing Gulls Leucophaeus atricilla, Royal Terns Sterna maxima, and Sandwich Terns Sterna sandvicensis) in relation to shrimp trawling activity in the nearshore waters of South Carolina from May to August, 2006 and 2007.Since 1992, numbers of breeding Brown Pelicans and Royal Terns have declined substantially in South Carolina, while the shrimp fleet has declined concurrently for economic reasons.We counted more than 36 000 birds in surveys conducted on 39 commercial trawler-days.All four locally breeding seabirds attended trawlers regularly, but pelagic seabirds were rare.Laughing Gulls were the most abundant species observed, and Laughing Gulls and Royal Terns were each observed on >90% of surveys.Seabird abundance was highest when trawlers were discarding bycatch.Spatial distributions varied among species but abundance of each species appeared to be relatively consistent out to 30 km from colonies.Given their abundance at trawlers, Laughing Gulls may be affected most strongly by the availability of discarded bycatch, but terns and Brown Pelicans forage at trawlers frequently enough that changes in the size of the shrimp fleet might affect their foraging ecology as well.