The fish fauna of the Scheldt basin in Wallonia

In 1978-1982, a survey of the fish fauna was carried out in the fresh waters of Wallonia including a study of a part of the Scheldt basin. A sample of 88 stations were fished with the electricity (direct current; single intensive catch-effort). Futher qualitative informations on the fish fauna in canalized navigable rivers and canals were obtained from questionnaires sent to anglers. This study allowed the assessment of the faunal resources (biodiversity), zoogeography (comparison between the Scheldt and Meuse basins), population dynamics (species extinction, demographic decline), relationship between the characteristics of the fish fauna and the water and habitat quality parameters, measures for conservation and management (species protection, reintroduction of species, stocking). Around the early 1980's the total number of indigenous species recorded in the Walloon part of the Scheldt basin amounted to 23, out of 44 species belonging to the Belgian freshwater ichtyofauna. Maps of the geographical distribution were produced for each species. Most of the fish communities are strongly altered by human influences : water pollution, river canalization, deepening and straitening, perturbation of fish mobility by small dams, weirs and sluices. Nevertheless, relict populations still locally exist in some well preserved habitats.