Geographical distribution and population status of Chondrostoma nasus in the river Meuse catchment area

C. nasus is not native to the R. Meuse basin (France, Belgium, The Netherlands) where it became established around the early 1800's following the connection by artificial waterways of western and eastern European river systems. At that time, C. nasus was recorded in the Belgian Meuse basin and in the River Scheldt near Antwerpen. C. nasus is currently extinct in the Scheldt basin. It is still occurring in the R. Meuse and several tributaries (especially the R. Ourthe, Lesse and Semois in the Belgian Ardennes) belonging to the grayling and barbel zones according to Huet's classification. Our research on the status of C. nasus populations reveals two opposite population trends : i) a recovery of C. nasus in stretches of the canalized navigable R. Meuse which were previously (fifties and sixties) polluted by industrial wastes and ii) a demographic decline of C. nasus in tributaries which supported dense populations in the fifties-sixties. Causes of this demographic decline of C. nasus in the Belgian barbel and grayling streams are likely to be linked with factors such as water quality (eutrophication), loss or alteration of key habitats (spawning and nursery grounds) and overexploitation by anglers. Current efforts aiming at stopping the decline of. C. nasus in the Belgian river Meuse basin include : i) studying the ecology of the species focusing mainly on the habitat requirements for spawning, first summer growth and wintering (importance of cover features); ii) opening the migration routes by building new efficient multi species fish-passes; iii) stocking streams with hatchery reared fingerlings of local origin and iv) improving angling regulations.