Pike as a Selective Predator. Effects of Prey Size, Availability, Cover and Pike Jaw Dimensions

An experiment was performed to study the influence of prey size, availability, the presence or absence of cover and pike jaw dimensions on prey consumption by pike. Rudd in schools of 10 were offered to pike in outdoor pools. Pike weighed between 66.4 and 182.1 g. Schools of 10 rudd contained two, five or eight fish with mean sizes between 5.6 and 6.8 g, the remaining fish weighing between means of 12.4 and 14.1 g. Cover was provided by a 1 m2 mat of plastic netting supporting simulated plant stems spaced at 5 cm intervals. Pike chose mostly from the small size category and the presence of cover did not significantly influence the choice made. Increased availability of the chosen prey size increased food intake. Pike never completely dropped the large prey from the diet despite its low availability; a case of partial preference. The jaw dimensions of the pike were most closely correlated with the body dimensions of the small rudd. It is suggested that the prey size eaten was determined by an interaction between pike jaw morphology and the relative swimming speeds of pike and rudd, rather than by a behavioural choice.