| Biomanipulations have often been used in small (<25 ha) shallow (<2.5 m mean depth) impoundments as a lake restoration technique. A biomanipulation was conducted on Campus Lake, a small southern Illinois impoundment, to improve water clarity. Specifically, 13,500 bluegill and 300 largemouth bass (30% and 15% of the estimated populations, respectively) were removed from the lake during fall 2006 and early spring 2007. Secchi depth, chlorophyll a concentration, zooplankton abundances, and total phosphorus (TP) were recorded as well as diet, annual growth rates, and size structure of bluegill, largemouth bass, and redear sunfish. Finally, bioenergetics models were used to determine the consumptive demand of bluegill and largemouth bass for prey. The biomanipulation did not significantly improve chlorophyll a or secchi depth due to high TP concentrations during the summer despite a significantly higher abundance of Bosmina after the removal. Diet analysis indicated that bluegill, largemouth bass, and redear sunfish feeding strategies were not altered due to the biomanipulation, and the annual growth rates of these fishes were not affected. However, the size structure of the bluegill population (proportional stock density (PSD)) was increased, and bluegill and largemouth bass population size structures (PSD) suggested a balanced predator-prey community. Bioenergetics modeling estimated that a bluegill removal of 75% would have been necessary to significantly reduce the consumptive demand of this species on cladocerans. Using biomanipulation to improve water clarity in Campus Lake is limited due to internal TP loading, especially during the summer. However, biomanipulation does appear to be a feasible technique for increasing the size structures (i.e., PSD) of fish populations. |
