Effects of Predation Risk and Foraging Return on the Diel Use of Vegetated Habitat by Two Size-Classes of Bluegills

Abstract

Little is known about nocturnal habitat selection by fishes under the risk of predation. Using a photoperiod of 15 h light : 9 h dark, we quantified the diel use of artificial macrophytes and open water by two size-classes of bluegill Lepomis macrochirus when the open water was empty (control), contained food, or contained both a caged predator and food. Small bluegills (6.2–7.7 cm total length) spent significantly more time in macrophytes in the predator and food treatment than in the control, followed by the food-only treatment. In addition, small bluegills spent significantly more time in macrophytes during the day than at night in all treatments. The frequency with which small bluegills were found in the same location in subsequent observations was significantly higher in the predator and food treatment during the day than in any other treatment and light combination. Large bluegills (10.2–13.0 cm total length) showed no difference in habitat use among treatments but spent significantly less time in macrophytes at night than during the day. There was no difference in the frequency with which large bluegills were found in the same location in subsequent observations among treatments or light levels. This suggests the potential for a diel littoral−pelagic habitat change by juvenile bluegills that would have important implications for the role of bluegills in lake food webs, including the possibility of nutrient translocation that could generate alternate stable states in lakes.