Meeting Abstract
Many drift-feeding fishes occupy high flow habitats that provide increased prey abundance but also incur a high cost of swimming. These fishes are thought to exploit hydrodynamic refuges to reduce energetic swimming costs. We show that the energetic cost and success rate of prey attacks are critical in determining whether refuging is energetically favorable for drift-feeding fishes. Using a flow tank respirometer, we systematically measured the oxygen consumption of rainbow trout (Oncorhynchus mykiss, 33.0±0.6 cm total length, 423±19 g) refuging behind a 5 cm D-cylinder or free swimming at variable flow speeds up to 100 cms-1. During feeding experiments, we used artificial prey to examine the energetics of repeated foraging attempts without the interference associated with the cost of digestion (i.e. specific dynamic action). We show that contrary to current belief, refuging is not an energetically beneficial strategy when foraging in high flow habitats due to the lower capture success rate and higher cost of prey attack. At flow velocities >50 cms-1, refuging causes a net energetic loss due to a 67% increase in the cost of attacking prey and a 40% reduction in attack success rate. This is most likely due to the cost of traversing a velocity gradient and tracking prey with unpredictable motions. Our results suggest that it is energetically most favorable to feed in the free stream during high flows and refuge when not feeding. Our data reveal that there is an energetic tradeoff between foraging and refuging behavior, which is influenced by prey size, prey abundance and flow velocity.
