Prey vulnerability to a gape-size limited predator: behavioural and morphological impacts on northern pike piscivory

The northern pike (Esox lucius) is a selective and important predator in la ke ecosystems. Prey size in pike is limited by pike gape size, which is a l inear function of pike body length. Here we show that the absolute gape-siz e limit in pike is greater than previously considered, and that maximum ing estible prey size is limited by prey body depth. Further, we experimentally show that pike prefer shallow-bodied roach before deeper-bodied common bre am, and small prey sizes within each prey species. Handling lime in pike in creases with prey body depth, and since common bream are deeper-bodied than roach, handling time is longer for bream than for roach of the same length , but equal considering body depth. Prey handling time is suggested to be a major cost to the pike, since it increases the risk of Losing the prey, as well as exposure to predation, kleptoparasitism and cannibalism. Consequen tly, prey vulnerability is determined by risk of predation and intraspecifi c interactions, and behavioural preferences in the pike, and not by pike ga pe-size limits. The consequences for natural populations is evaluated by an alysing size structures of predator and prey fish populations in a eutrophi c lake.