THE INFLUENCE OF INSTREAM COVER AND PREDATION RISK ON MICROHABITAT SELECTION OF STONE LEACH BARBATULA-BARBATULA (L.)

The microhabitat selection of stone leach (Barbatula barbatula) in rel ation to instream cover and predation risk was investigated in artific ial streams. In one experiment, stone leach were presented different c ombinations of shelter structures, two at a time, that provided visual isolation, flow refuge, both, or none. In all cases, visual isolation shelters were selected by the fish, with little use of clear shelters and no apparent selection of flow refuges. In a second experiment, di el activity patterns and habitat selection of stone leach were measure d when visual isolation structures were placed in the riffle only, poo l only, both riffle and pool or in no habitat. Stone leach were marked with passive integrated transponder tags and a sensor plate was place d between the riffle and pool habitats to measure diel activity patter ns. Habitat use was measured by releasing drop gates between the two h abitats at the end of each trial. More stone leach used the pool than the riffle in all treatments, but use of the riffle increased when cov er was present only there. Furthermore, stone leach were most active b etween 2100 and 0300. To determine the effect of predation threat on h abitat use by stone leach, one adult brown trout (Salmo trutta) was ad ded to each pool. The presence of trout caused stone leach to move int o the riffle, especially the smaller leach. Overall, the study showed that stone leach used cover in a visual isolation context, preferring deeper water when there was no predation risk, but made more use of sh allower water in the presence of brown trout.