Oxygen consumption of drift-feeding rainbow trout: the energetic tradeoff between locomotion and feeding in flow
To forage in fast, turbulent flow environments where prey are abundant, predatory fishes must deal with the high associated costs of locomotion. Prevailing theory suggests that many species exploit hydrodynamic refuges to minimize the cost of locomotion while foraging. Here we challenge this theory based on direct oxygen consumption measurements of drift-feeding trout (Oncorhynchus mykiss) foraging in the freestream and from behind a flow refuge at velocities up to 100 cm s-1. We demonstrate that refuging is not energetically beneficial when foraging in fast flows due to a high attack cost and low prey capture success associated with leaving a station-holding refuge to intercept prey. By integrating optimum foraging theory with empirical data from respirometry and video imaging, we develop a mathematical model to predict when drift-feeding fishes should exploit or avoid refuges based on prey density, size and flow velocity. Our foraging and refuging model provides new mechanistic insights into the locomotor costs, habitat use, and prey selection of fishes foraging in current-swept habitats.