Selection between Densities of Artificial Vegetation by Young Bluegills Avoiding Predation

Abstract

Young (35–50 mm, standard length) bluegills Lepomis macrochirus are restricted to vegetated habitats by predation pressure. Vegetation provides refuge by hindering predator foraging success. In this study, we tested the ability of bluegills to actively perceive and select densities of vegetation where they are safe from predation. Bluegills were presented with two plots of artificial vegetation (cover plots) of different densities (1,000, 250, 100, and 50 stems/m2) in an experimental arena and then confronted with a predator, a largemouth bass Micropterus salmoides. Prey distribution in the arena before, during, and after exposure to the predator, as well as the predatorˈs foraging activities, were recorded for each trial. Before predator introduction, bluegills in all combinations of cover plots spent most of their time in or around the thicker plot of vegetation in the arena. With the predator present in combinations with cover plot 1,000, prey chose this plot as a refuge when attacked. Cover plot 250 was selected as often as positions at the water-air interface, and plots 100 and 50 were ignored as refuges. After removal of the predator, only in combinations with cover plot 1,000 did prey remain around the thicker cover plot present. Predator success (number of prey caught/total number of attacks) was lowest in trials with cover plot 1,000 present. When confronted with a predator, young bluegills appear capable of perceiving and selecting plots of vegetation offering safety from predation.