Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Wildlife and Fisheries Biology

Advisor

Jodice, Patrick G.

Committee Member

Powell , Robert

Committee Member

Rieck , James

Abstract

Population dynamics of seabirds have been linked to the availability of bycatch discarded from commercial fishery operations. This issue has been examined primarily in Europe where studies demonstrated that tens of thousands of seabirds each year may be supported by discards from a regional fishery, and that discards from commercial fisheries contributed to the increase in seabird abundance and to changes in their distribution in the North Sea and Northeast Atlantic. To date, however, little to no research has been conducted on seabird-fisheries interactions in the United States. This research examined this issue in the coastal waters of South Carolina where populations of two common seabirds, brown pelicans (Pelecanus occidentalis) and royal terns (Sterna maxima), are declining but where two other species, laughing gulls (Larus atricilla) and sandwich terns (Sterna sandvicensis) are increasing. The South Carolina coastal region also supports a substantial commercial shrimping industry that operates primarily in inshore waters and has fluctuated greatly in fleet size during the past two decades. This research investigated the relative abundance and distribution of ship-following seabirds at shrimp trawlers during the seabird breeding season, determined the composition of bycatch, particularly items that are appropriately sized for capture by seabirds, and also measured the consumption fate of fish species collected as bycatch. Shrimp trawlers appeared to be a strong, local attractor for seabirds out to 30km from the nesting colonies. All of the four locally breeding seabird species attended trawlers regularly, and the most generalist of these, laughing gulls, were the most abundant and frequently observed. Trawler activity, (i.e., phase of the trawler operations) was the factor which most affected the abundance in seabirds and spatial distributions varied from species to species. Brown pelicans consumed more discards than predicted based on their frequency while the other three seabirds each consumed fewer discards than predicted based on their frequency. Seabirds selected smaller discard items compared to larger items, and selected benthic fish (i.e., drum species) that typically would not be available to this suite of seabirds. Approximately 70% of the discarded bycatch in experiments was consumed by seabirds, suggesting that bycatch possibly makes up a large part of their diet at certain times of year (i.e., breeding months). My findings suggest that laughing gulls may be affected most strongly by the availability of additional food via discarded bycatch but that tern species as well as brown pelicans forage at trawlers frequently enough that changes in the size of the shrimp fleet would have the potential to affect their foraging ecology as well.

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