An Index of Biotic Integrity characterizing fish populations and the ecological quality of Flandrian water bodies

A multimetric fish Index of Biotic Integrity (IBI) was composed to assess t he biotic integrity of Flandrian water bodies. As fish communities differ s ubstantially between standing waters, running waters of the bream zone and running waters of the barbel zone, eight candidate metrics for each of thes e water types or zones were identified, representing three major classes of biological attributes. These are species richness and composition, fish co ndition and abundance, trophic composition. The metrics were tested and mod ified where needed. The IBI was applied throughout Flanders on 104 location s in standing waters, 500 locations in waters of the bream zone and 257 loc ations in waters of the barbel zone. Standing waters scored substantially d ifferent from running waters. Standing waters rarely contained no fish at a ll, but their fish communities were very often poor to very poor. Waters of the bream and barbel zone were often fishless (respectively 40% and 35% of all locations contain no fish), but the locations with fish usually scored reasonable to poor. Only 18.5% of all locations were classified as reasona ble to excellent (IBI classes 4 or lower on a scale from 1 to 9) and were c onsidered to satisfy the basic ecological quality demands. The Leie-, Dijle -, Dender- and Schelde-basins had a very poor quality (more than 50% of the locations contained no fish). The Maas-, Grote and Kleine Nete-basins scor ed rather well, with respectively, 44%, 48% and 68% of the locations achiev ing an IBI of 4 or lower. The IBI is a valuable and complementary tool to a ssess the ecological quality of water bodies as suggested in the proposal f or a Water Framework Directive by the European Commission.