Common tern foraging: seasonal trends in prey fish densities and competition with bluefish.

Studied foraging behavior of Sterna hirundo in relation to density of fish prey off Long Island, New York, using an echo sounder to record the abundance of small prey fish and large predatory fish near a tern colony. Prey fish abundance was highest when terns were feeding young chicks and declined sharply later in the season, coincident with the arrival of large numbers of predatory bluefish Pomatomus saltatrix. Mean depth of occurrence of prey fish was shallower after arrival of bluefish. Terns fished in areas with high concentrations of prey, but there was no correlation between number of feeding terns and prey density. Number of feeding terns was inversely correlated with prey depth. Terns were strongly attracted to predatory fishes feeding near the surface. In addition to concentrating prey fish near the surface, predatory fish may have been important as competitors.-from Authors Sterna hirundo Pomatomus saltatrix Long Island New York