Diet of the Neotropical Cormorant (Phalacrocorax brasilianus) in a Patagonian Freshwater Environment Invaded by Exotic Fish

The diet of the Neotropical Cormorant (Phalacrocorax brasilianus) was evaluated in the Limay River basin, a freshwater system invaded by exotic salmonids. Analyses of 106 pellets showed that fish were the most important prey (79.9% by numerical frequency, and 86.2% by frequency of occurrence), followed by two crustacean species. Among fish, the most common species were exotic salmonids, representing 84% by numerical frequency. Morphometric comparisons enabled differentiation of sagitta otoliths from Oncorhynchus mykiss and Salmo trutta and permitted determination of similar contributions of these species to the diet. Although a wide prey-size range was found, 85% of fish were smaller than 150 trim in length. The results suggest that the Neotropical Cormorant has adapted to changes in the fish community: after the introduction of salmonids. Flexible feeding strategies of the Neotropical Cormorant and/or its capacity to exploit different environments probably make it less vulnerable to environmental changes produced by introduction of exotic fish. Received 21 March 2011, accepted 17 November 2011.