Diet shift of double-crested cormorants in eastern Lake Ontario associated with the expansion of the invasive round goby

Abstract

The proliferation of the invasive round goby (Apollonia melanostoma) in the Great Lakes has caused shifts in the trophic ecology in some areas. We examined the diet of double-crested cormorants (Phalacrocorax auritas) prior to, and immediately after, round goby population expansion at two colonies, Pigeon and Snake Islands, in eastern LakeOntario from1999 to 2007. Cormorantdietwas determined fromthe examination of 10,167 pellets collected over the nine-year period. By the second year round gobieswere found in the diet (2002 at Snake Island and 2003 at Pigeon Island) they were the main species consumed by cormorants at each colony. The dominance of round goby in cormorant diets had a significant effect on both daily fish consumption and seasonal trends in fish consumption compared to the pre-goby years. Seasonal differences thatwere observed during the pre-goby years were lost once gobies becamethemain diet component of cormorants. The rapid switch to a benthic prey such as round goby, from a largely limnetic fish diet demonstrates the adaptive foraging ability of cormorants. Round goby may act as a buffer for yellowperch and smallmouth bass, two sport fish impacted by cormorant predation in eastern Lake Ontario. © 2010.