Summary
Juvenile bluegill sunfish, Lepomis macrochirus, are known to use beds of aquatic vegetation as a refuge from predators. This study examines the effects of increasing plant stem density on juvenile bluegill foraging. Three stem densities (100, 250 and 500 stems m−2), varying in their refuge potential for bluegills from predators, were tested. Results demonstrate that stem densities chosen as a refuge from predation (i.e. 500 stems m−2) significantly reduced bluegill foraging success and increased time required to capture prey. Therefore, juvenile bluegills seeking safety in vegetation may be faced with a trade-off between foraging success and effective refuge from predation when choosing among plant stem densities.
Methodology
Bluegill sunfish (35–50 mm, standard length) were collected from weed beds in Lake Opinicon, Ontario (40° 30’ N 76° 30’ W) by seining. This size range of bluegill is restricted to vegetated habitats by predators (Werner et al. 1983b). Fish were brought back to the laboratory at Queen’s University, Kingston, Ontario, where they were housed in flow-through tanks (56 x 53 x 30 h cm) at 20–24°C, and a light regime of 12 h L: 12 h D. While in the holding tanks fish were fed grated frozen fish.