Fish Community Responses to Half-Log Additions in Warmwater Streams

Abstract

Half-log habitat enhancement structures are commonly used for stream restoration projects to increase fish abundance and biomass. Half logs (N = 108) were added to nine headwater streams of the upper Wabash River basin, Indiana, in July 2003. Study sites (25 m in length) were sampled with backpack electrofishing once each month during July–October 2003 and April–September 2004 to document the colonization and use of half logs by fish under agriculture, forest, and fallow-field land uses. Index of biotic integrity (IBI) scores did not change significantly after half-log additions. The effects of half-log habitat enhancement structures were variable by month, stream, and in some cases, individual fish species. Species richness and biomass significantly increased in two study streams during spring and fall due to the presence of bluntnose minnow Pimephales notatus and longear sunfish Lepomis megalotis. Absolute abundance within most sites increased during periods of low flow and high temperature in late summer and early fall, when fish are most vulnerable to predation and require habitat refugia. Fish use of half logs was also dictated by the amount of instream habitat, especially where percentages of aquatic vegetation (mean = 0.0%) and large woody debris (mean = 0.67%) were low and the percentage of pool habitat was moderate (mean = 10.53%). In this study, we found that with the exception of IBI scores, significant manipulation response was variable by stream and species and was influenced by instream habitat and time of year.