DIVERGENT DISTRIBUTIONS OF PREY AND PREDATOR, A FISHING EFFECT

To compare the vertical distributions of benthos and fish species of U pper Lake Constance (Bodensee), 552 benthos samples were taken with an Auerbach grab at four transects (10-250 m). An additional 54 samples (1-10 m) were collected elsewhere. Complementary data was taken from t he literature. In winter, most fish feed on benthos, mainly chironomid s, but in summer less than 5% do so. Formerly the bottom gill-netting aimed mainly at catching Coregonus pidschian, but it now aims at Perca fluviatilis. Contrary to expectation, in winter the greatest abundanc e of P. fluviatilis is much deeper (55 m) than that of its preferred f ood, i.e. chironomids (<20 m). Comparably, C. pidschian also stayed de eper than its main food source (chironomids and mollusks). Lota lota, Salvelinus profundus and S. alpinus - unlike the unwanted cyprinids - also stay or stayed deeper than the attractive chironomids. It is argu ed that the fish reduce their ''predation risk'', i.e. the risk of bei ng gillnetted in the upper 50 m, by ''selecting'' the deeper less dang erous, but also less food-abundant habitat. Balancing predation risk a gainst food abundance may have led to ''survival of the deepest''.