Effects of prey species composition and habitat structure on foraging by two functionally distinct piscivores

We compared foraging by two piscivores, pike (Esox lucius) and zander (Stizostedion lucioperca), on two prey fishes, crucian carp (Carassius carassius) and rudd (Scardinius erythrophthalmus), in the presence and absence of artificial vegetation in a field enclosure experiment. We found that pike had a higher predation rare than zander in the presence of vegetation, whereas zander had a higher predation rate in the absence of vegetation. In addition, both piscivores selected crucian carp over rudd, resulting in higher survival of rudd in the presence of crucian carp. Behavioral observations of the prey in the presence of artificial vegetation showed that rudd moved rapidly in shoals, spending relatively little time in vegetation, whereas crucian carp moved considerably less and spent more time in vegetation. The presence of either piscivore caused crucian carp, but not rudd, to increase its use of vegetation. Ln addition, both prey species moved more rapidly in the enclosures when vegetation was absent than when it was present. The increased movements of crucian carp were due to crucians shoaling with rudd. Our data are consistent with the notion that the structure of many European fish assemblages is related to differential vulnerability of prey species as well as differential foraging success of piscivores in open water and vegetation.