Use of fishing discards by breeding Kelp Gulls in Northern Golfo San Jorge

The Kelp Gull (Larus dominicanus) is a generalist species that includes in its diet food derived from human activities. The Parque Interjurisdiccional Marino Costero Patagonia Austral in northern Golfo San Jorge, Chubut, constitutes one of its most relevant breeding areas, and trawl fisheries operate in its adjacent waters to which it associates to take advantage of fishing discards. The main discarded component is the Common Hake (Merluccius hubbsi), a demersal species that is not normally available to surface feeding seabirds. In order to assess the interaction between the Kelp Gull and fishing activities, we analyzed the spatial association with operating vessels and diet of breeding individuals from Isla Vernacci Este during the incubation stage of 2015. We tracked 11 breeders using global positioning system loggers, recording 56 foraging trips which showed a mean maximum distance from the colony of 26.4 ± 11.9 km. Ten of the instrumented individuals mainly made offshore foraging trips and only one made trips exclusively to intertidal zones. The spatial overlap with fishing operations was 76%. The analysis of stomach samples (n=29) showed that 96% comprised fish, being Common Hake (FO=50%) and Anchovy (Engraulis anchoita) (FO=42%) the two most frequent prey. Results confirm that Kelp Gulls breeding in the Marine Park take advantage of food provided by fisheries and suggest the need to coordinate management actions within and outside the protected area.