Importancia de los descartes pesqueros en la dieta de la gaviota cocinera (larus Dominicanus) en el golfo san jorge, patagonia

Abstract

The consumption of fishery discards at sea is currently an important component in the feeding ecology of many gull species. Diet studies are key to assess the relative contribution of discards in their trophic ecology, and to start to understand the potential effects of fishing activities on their breeding parameters and population dynamics. The present study analyzes the dietary composition of Kelp Gulls (Larus Dominicanus) breeding on the northern coast of Golfo San Jorge, Chubut, Argentina, during the 2007 breeding season in three sites: Isla Vernacci Sudoeste (45°11’S, 66°31’O), Isla Felipe (45°04’S, 66°19’O) and Isla Laguna (45°02’S, 65°53’O). Three sampling periods were selected: incubation, small chicks and large chicks. Diet samples were obtained through stomach flushing. The results obtained in the three colonies analyzed confirm that on the northern Patagonian coast the Kelp Gull is a generalist and opportunistic species that feeds during the breeding season on a wide variety of prey, mainly fish and marine invertebrates. During the large chick stage, frequency of occurrence of fish increased while that of polychaetes decreased. Fish were the most frequent prey in the Golfo San Jorge, represented mainly by the Argentine hake (Merluccius hubbsi), a demersal species that is in general inaccessible for surface predators like the Kelp Gull. It is highly likely that Argentine hake consumed by Kelp Gulls comes mainly from fishing discards. Future studies should evaluate spatio-temporal patterns in the distribution of fishing vessels and their relation with the proportion of fishery discards in Kelp Gull diet.