Bluegill sunfish (Lepomis macrochirus) are common to lakes and ponds of the Midwest and are often considered a key player in the aquatic community. While several studies have examined reproduction in bluegill, especially their mating system, relatively little information exists on the basic nesting ecology of bluegill sunfish, particularly from populations in small ponds. We investigated nest characteristics, seasonal activity of nests, and colony activity in a small pond (~1.6 ha) for two summers. Essentially we were interested in finding out if variables that define the nesting environment, such as colony size, proportion of active nests, timing of peak nesting activity, and nest traits such as depth and size, varied between years. We marked, mapped, and surveyed all nests in Middleton Pond 2-3 times per week from May through August in 2005 and 2006. For each survey we recorded the status of the nest (e.g., unused, cleared, male present, eggs present, etc.). We also recorded nest traits such as bowl depth, maximum diameter, and proportion of overhead vegetation/shading for a subset of active and unused nests.
Results/Conclusions
We identified and surveyed 551 possible nest sites in 2005 and 497 possible nest sites in 2006. Pond depth decreased about 0.5 m from 2005 to 2006 resulting in the loss of some nest sites previously used for breeding in 2005. The bluegill population showed several peaks in nesting activity each year, but the timing of these peaks differed between years. In both years we found that at least a few males were actively maintaining nests on each survey date, thus breeding efforts did not entirely cease at any point during the summer. In examining colonies in the pond we found that the number of active colonies differed between years, with more in 2006 than in 2005. We found that active nests had deeper bowls of greater diameter compared to inactive nests and we found that nests or colonies with high activity had higher levels of shading or overhanging branches. These results point out that bluegill populations in small ponds may have different nesting experiences each year as some aspects of the nesting environment change from year to year.