THE INFLUENCE OF PREDATION RISK ON HABITAT SELECTION AND FOOD-INTAKE BY ARCTIC CHARR, SALVELINUS-ALPINUS (L)

Large piscivorous fish are assumed to affect habitat selection and foo d intake of prey fish. To study the effects of cannibalistic Arctic ch arr, Salvelinus alpinus (L.), on smaller stunted charr, we sampled the prey fish in littoral and pelagic habitats using gill nets, before an d shortly after the release of large charr in a small lake (0.52 km(2) ). In the habitats where the risk of predation was highest, the catch per unit effort decreased from 13.3 to 4.8 fish per 100 m(2) of gillne t after release of predators. The large decrease in numbers of charr < 18 cm corresponded with the predicted vulnerable prey sizes, according to a model based on the size distribution of predators. The occurrenc e of planktivorous fish and weight-specific food intake decreased in t he high risk habitat and remained unaffected in the low risk habitats. Changes in the food intake of prey fish could not be explained in ter ms of fish length, indicating that prey fish changed diet when the ris k of predation was high.