Energetic factors influencing foraging tactics of juvenile steelhead trout, Salmo gairdneri

Abstract

Increases in water temperature and fish size should increase standard metabolism and food demand. Stream dwelling trout may then, despite the increased cost of swimming, seek faster water where food is more abundant. We tested these predictions with juvenile steelhead trout, Salmo gairdneri, in a California stream and found that increased fish size and water temperatures did result in the increased selection of microhabitats with high water velocities. Faster water provided proportionally larger amounts of drifting invertebrate food. Higher velocity, shallower, and coarser substrate microhabitats also enabled fish to capture prey form portions of the water column substantially faster and more productive than at their resting positions. Velocities selected in this stream were similar to those which would result in a doubling metabolic rate. Models evaluating trout habitat and effects of modifications should take energetic factors into account.