Kelp gull population trends in northern Patagonia, Argentina: a regional perspective considering artificial food sources

NORA LISNIZER; PABLO GARCÍA BORBOROGLU; PABLO YORIO

Victoria, Canadá

Congreso; 1° World Seabird Conference; 2010

Food availability is a key factor influencing seabird population dynamics. The Kelp gull Larus dominicanus is widely distributed in the Southern Hemisphere, including the Atlantic coast of Argentina. It is a generalist species that feeds on a wide variety of food from natural and artificial sources. We analyzed Kelp gull population trends at 71 colonies in northern Patagonia, Argentina (1800 km of coastline, from 40°47’ to 46°00’S), considering the relationship of colonies with artificial food sources (fisheries discards and landfills). We used recent census of breeding pairs (2006-2008) integrated with unpublished and published information, extending over a 15-year period (1994-2008). We analyzed the population trend for the whole study area and then for the same set of colonies divided into four coastal sectors characterized by differences in the characteristics of artificial food sources. We tested for differences in population growth rates among sectors by fitting linear regression models and comparing regression slopes. The Kelp gull population in the study area increased 52%, from 47500 to 72000 breeding pairs (l=1.027). Population growth rates showed significant differences (p<0.05) among sectors, and trends mirrored the differential availability of artificial food sources. The northern and southernmost sectors, where availability of fish waste was greatest, showed higher rates of increase (l=1.049 and 1.046, respectively) than central sectors (l=0.989 and l=0.999) where available artificial food was lower. Our results show the marked increase in the breeding population and suggest the importance of artificial food sources, specially fisheries discards, on Kelp gull demography in Patagonia, Argentina.