Foraging among cannibals and kleptoparasites: effects of prey size on pike behavior

The northern pike (Esox lucius) is an important and selectivepiscivorethat chooses smaller prey than predicted from energy / timebudgets.In a laboratory experiment, we investigated pike predatorybehavior to explainthis selectivity. Northern pike feedingon different prey sizes in aquariawere observed when foragingalone, when in the presence of chemical cues fromsimilar-sizedor larger conspecifics, and when in the presence of conspecificsthatwere allowed to interact with the focal pike. The results showthat preyhandling time increases with prey size and that theduration of manipulatingand handling prey inflicts a risk ofexposure to cannibals and kleptoparasiteson the pike. Therefore,the risk of falling victim to cannibals orkleptoparasites increaseswith prey size. Attracting and experiencingintraspecific interactorscan be regarded as major fitness costs. Chemicalcues from foragingconspecifics have only minor effects on pike foragingbehavior.Furthermore, the ability to strike and swallow prey head firstimprovespike predatory performance because failing to do so increaseshandlingtime. Our findings emphasize the increasing potential costswithlarge prey and explain previous contradictory suggestionson the underlyingmechanisms of behavior, selectivity, and trophiceffects of northern pikepredation.