Modelling the Effects of Current on Prey Acquisition in Planktivorous Fishes |
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Authors: | William McFarland Simon Levin |
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Institution: | 1. School of Aquatic and Fisheries Sciences and Friday Harbor Laboratory , University of Washington , Friday Harbor, WA, 98250;2. Department of Ecology and Evolutionary Biology , Princeton University , Princeton, NJ, 08544-1003 |
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Abstract: | Many planktivorous fishes forage in currents, where they actively maintain position and visually strike at current-entrained zooplankton. In general, the zooplankton are wafted by the foraging fish at a rate equivalent to the current velocity. From a fish's viewpoint the plankton approach either head-on or offset at varied distances from the fish's position. We present a model that describes the relative motion of particles as they approach and pass a foraging fish at different offset distances, and the rate of change in apparent size as they close on a fish. In addition, a series of experiments of fish feeding on plankton in a flume at increasing current velocities revealed that two basic tactics are utilized. At low current velocities (<10-14 cm s m 1), the fish swims toward the prey, whereas at higher current velocities the fish tends to fall back with the current to capture a prey item. The model and experimental results are discussed in terms of the visual problems associated with the detection and tracking of items in motion. |
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Keywords: | Current Velocity Relative Motion Plankton Loom Planktivorous Fish |
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