Contribution à l'étude de l'écosystème "rivière de la zone à barbeau supérieure" : densité, biomasse et production des populations de poissons dans l'Ourthe

In the fish community (23 spp.) of the upper barbel-zone of the River Ourthe (River Meuse basin, Belgium) 3 large rheophilic cyprinids (barbel Barbus barbus, nase Chondrostoma nasus, chub Leuciscus cephalus) and 2 salmonids (brown trout Salmo trutta, grayling thymallus thymallus) make up about 90 % of the total biomass caught by electrofishing in a 9,6 km (26,9 ha) reach of the river. Mark-recapture experiments performed in the same reach by late summer 1973 give estimates of absolute density (1321+/_ 83 fish/ha; juveniles not included) and biomass (286,9 +/_ 18 kg/ha) for 7 species. Annual production of the catchable part of two of the studied populations amounted to 4,77-6,42 kg/ha and 13,77-15,78 kg/ah respectively for the chub (> 2 ++; somatic production only) and for the nase (>3++, somatic + sexual production). Results for other species are not yet available. Production data presented in this report must be improved by complementary treatments.