Bluefish mediation of foraging competition between roseate and common terns

The presence and foraging activities of predatory bluefish Pomatomus saltatrix differentially affect the foraging success of roseate Sterna dougallii and common terns S. hirundo, and depress the foraging activities of roseate terns. In the absence of bluefish, roseate terns had higher mean fishing success frequencies than common terns, an advantage lost in the presence of bluefish, and roseate tern foraging success was inversely correlated with bluefish feeding intensity. Roseate terns left foraging flocks more frequently as predatory fish activity increased and flock density increased. The rate at which common terns left flocks was inversely correlated with predatory fish feeding and was unrelated to flock density. Bluefish may be considered keystone competitors in this system. -Author