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

The northern pike (Esox lucius) is an important and selective piscivore that chooses smaller prey than predicted from energy / time budgets. In a laboratory experiment, we investigated pike predatory behavior to explain this selectivity. Northern pike feeding on different prey sizes in aquaria were observed when foraging alone, when in the presence of chemical cues from similar-sized or larger conspecifics, and when in the presence of conspecifics that were allowed to interact with the focal pike. The results show that prey handling time increases with prey size and that the duration of manipulating and handling prey inflicts a risk of exposure to cannibals and kleptoparasites on the pike. Therefore, the risk of falling victim to cannibals or kleptoparasites increases with prey size. Attracting and experiencing intraspecific interactors can be regarded as major fitness costs. Chemical cues from foraging conspecifics have only minor effects on pike foraging behavior. Furthermore, the ability to strike and swallow prey head first improves pike predatory performance because failing to do so increases handling time. Our findings emphasize the increasing potential costs with large prey and explain previous contradictory suggestions on the underlying mechanisms of behavior, selectivity, and trophic effects of northern pike predation.