Biomanipulation in shallow lakes : state of the art

Present knowledge on the biomanipulation of shallow lakes, obtained from the literature and the Shallow Lakes Conference 1995, is reviewed. Establishing clear water, maintaining it, and stabilizing the improved system are discussed. Biomanipulation aimed at a clear water system which was macrophyte-dominated. It was critical to understand the factors causing turbid water. With sufficient information it might be possible accurately to target particular components of the fish community: without this knowledge, a 75 per cent removal of fish and possibly some stocking with piscivores was the best approach. Biomanipulation was best undertaken in winter to encourage spring grazing by zooplankton and the longest possible period of clear water for macrophytes to establish. The process might need repetition if macrophytes did not establish. A relative increase in piscivorous stock and a reduction in nutrient levels favoured stability. Whether biomanipulation could result in alternative equilibria involving high phosphorus concentrations was unknown. Theoretical modelling and studies of more long-term investigations were desirable. There are 108 references.