POSITION CHOICE BY DRIFT-FEEDING SALMONIDS - MODEL AND TEST FOR ARCTIC GRAYLING (THYMALLUS-ARCTICUS) IN SUB-ARCTIC MOUNTAIN STREAMS, INTERIOR ALASKA

Assumes that a fish chooses the position that maximizes its net energy intake rate. The fish's habitat is represented as a series of stream cross-profiles, each divided into vertical strips characterized by water depth and velocity. The fish may select a focal point in any of these strips, and include several neighbouring strips in its foraging area. Number of prey the fish encounters depends on its reaction distance to prey, water depth, and water velocity; proportion of detected prey the fish is able to capture declines with water velocity. The fish's net energy intake rate is its gross energy intake rate from feeding minus the swimming cost calculated by using water velocity at the fish's focal point. -from Authors