Great Black-Backed Gull (Larus marinus) Predation on Seabird Populations at Two Colonies in Eastern Canada

Abstract

Abstract. The increase in gull (Laridae) populations through the 20th century, largely due to an upsurge in anthropogenic food sources, has raised concerns about the effects of gulls on sympatric populations of other seabirds. In Newfoundland and Labrador, Canada, a reduction in fisheries discards due to the collapse of cod (Gadus morhua) populations and a phenological delay in the early 1990s and early 2000s in spawning capelin (Mallotus villosus) has supposedly resulted in increased seabird predation by gulls. Accordingly, the diet of Great Black-backed Gulls (Larus marinus) was quantified at two colonies (Gull Island, Witless Bay, Newfoundland, and Gannet Islands, Labrador), and the total mortality on sympatric breeding seabirds at each site was extrapolated. At the Gannet Islands, Great Black-backed Gulls primarily kleptoparasitized Atlantic Puffins (Fratercula arctica) bringing sandlance (Ammodytes sp.) to their chicks, whereas at Gull Island, seabirds formed the bulk of the gulls' diet. Great Blackb...