Assessment of backwater lake management strategies based on the diets of five riverine fishes

Abstract

Swan Lake, an Illinois River backwater, has been affected by sedimentation, altered hydrological patterns, and aquatic vegetation loss. This degradation led to a habitat rehabilitation and enhancement project where the lower portion of the lake was divided into two management units, with varying connectivity to the river and frequency of lake drawdowns to compact sediments. We assessed effects of these strategies on fish habitat by analyzing the diets of five riverine fishes in 2005 and 2006. Even though habitat improvement was in its early stages, diet analysis suggested that the frequent drawdowns of the middle unit created a better fish foraging habitat. During the summer, common carp and orangespotted sunfish consumed more prey items in the middle unit where frequent drawdowns occurred relative to the lower unit where only one drawdown was conducted. Additionally, caloric intake by common carp was greater in the middle unit during both summer and winter and for crappie during the winter. The single drawdown of the lower unit did not result in the desired sediment consolidation, which likely contributed to the poor foraging habitat.