Ecological Implications of Fish Removal: Insights from Gut-Content Analysis of roach (Rutilus rutilus) and European perch (Perca fluviatilis) in a Eutrophic Shallow Lake

Large reductions in fish biomass are common both as a method of managing lake ecosystems by fish removals (biomanipulation), and as naturally occurring fish kills. To further understand how fish reductions change feeding patterns of fish we studied the diets of small-medium sized roach (Rutilus rutilus) and European perch (Perca fluviatilis) on a monthly basis using gut-content analysis during an 18-month period before and following a whole lake fish removal in a eutrophic shallow lake. Further, we performed in-depth analyses of zoobenthos communities of the profundal and littoral zones, as well as analyzing the zooplankton community in the littoral and pelagic part of the lake to estimate abundance and biomass of potential diet items. We found that, in general, there was a trend towards increased zoobenthivory in both species and among all sized fish after the fish removal, regardless of prior diet preference. Reduced piscivory among larger perch (>150 mm), and reduced zooplanktivory among smaller perch and roach (