Diet of Double-Crested Cormorants in New York Harbor

Double-crested Cormorants,  Phalacrocorax auritus, have been breeding in New York Harbor since 1986 but the local diet has not been studied until now.  During the breeding and chick rearing seasons of 2006-2011 pellets and boli were collected in the New York Harbor area. The results indicate a diet encompassing 46 species of fish, and six species of crustaceans, and including species associated with marine, estuarine and freshwater environments.  Frequent species included scup, Stenotomus chrysops, and black seabass, Centropristis striata.  Species of interest to local fishermen such as striped bass, Morone saxatilis, and winter flounder, Pseudopleuronectes americanus, were identified in the samples in low numbers.  Differences were noted between species found in boli and those found in pellets.  One possible explanation appears to be the presence of spines in the fins of prey species – fish with spines in their fins comprised 50% of the items in boli and 95% of items in pellets.  Our results indicate that the population is not currently in competition with local fishermen.  The difference in results between pellets and boli highlights the issues involved in the use of pellets for diet analysis.