Prey Location Volume of a Planktivorous Fish: A New Measure of Prey Vulnerability

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Abstract
The probability that bluegills (sunfish) (Lepomis macrochirus) will locate prey varies with distance and position of the prey in three-dimensional space. Location ability is greatest in the hemisphere directly ahead of the fish. The probability that bluegills will locate prey declines steadily when prey are placed to the side, behind, or directly above or below the fish. Bluegills could locate prey farthest when placed slightly to the side of the area directly in front of the fish. Under all experimental conditions, fish could locate prey, at least some of the time, at distances considerably farther than suggested by reported reactive distance measurements, indicating that the water volume searched by bluegills has generally been underestimated.Key words: planktivorous fish, zooplankton, reactive distance, location volume, predator search