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.

The effect of vegetation density on juvenile bluegill diet and growth

“…Because piscivorous fish were not present in the ponds, it was surprising that bluegill foraged so heavily in the vegetated habitat. Shoup et al (2003) found that bluegill in the laboratory spent 40-80% of their time in artificial macrophytes even in the absence of a predator and when food was only available in the open water. Either bluegill cannot accurately assess predation risk or some other mechanism causes bluegill to forage in vegetated habitat.…”

“…However, structurally complex habitats can reduce foraging return and growth rate of juvenile fishes (Persson 1991;Diehl and Eklov 1995;Shoup et al 2003). The optimal diet for juvenile bluegill (Lepomis macrochirus) is often considered to be pelagic zooplankton (Mittelbach 1981).…”

“…Yet juveniles often forage suboptimally in structurally complex habitats, such as dense vegetation, to avoid pelagic predation risk (Mittelbach 1981), which can be a major factor determining recruitment to age-1 (Santucci and Wahl 2003). Studies of bluegill behavior in the laboratory (Gotceitas and Colgan 1987;Savino and Stein 1989;Shoup et al 2003) and in ponds (Werner et al 1983a) both show that bluegill spend more time in structurally complex habitats when predators are present. Furthermore, structurally complex habitats can negatively affect foraging returns of juvenile bluegill (Mittelbach 1981;Gotceitas 1990a;Pothoven et al 1999), and vegetation density negatively correlates with bluegill growth (Shoup et al 2007).…”

Relationships among biological elements (macrophytes, macroinvertebrates and ichthyofauna) for different core river types across Europe at two different spatial scales

“…Vegetated habitats are important refuge areas against high currents and aquatic predators, particularly for small fish (e.g., Allouche, 2002;Shoup et al, 2003). For invertebrates, the pattern of greater richness may result from higher hydrodynamic disturbance in mountain rivers, (Townsend, 1989;Voelz & McArthur, 2000;Wright & Li, 2002;Willis et al, 2005).…”

Predation of invasive crayfish on aquatic vertebrates: the effect of Procambarus clarkii on fish assemblages in Mediterranean temporary streams

“…Crayfish have been implicated in the decline of fish populations mainly indirectly due to competition for food and shelter (Guan and Wiles 1997, Miller et al 1992, Gherardi 2002, Nyström 2002, Light 2005 and through the destruction of macrophyte beds, which are important habitats for juvenile fish (Rubin and Svensson 1993, Scheidegger and Bain 1995, Shoup et al 2003.…”