Trends of a bitterling (Rhodeus sericeus) population in a man-made ditch network

This study describes the trends of a bitterling population in the Bourgneuf Marsh in relation to human activities. Although there were no bitterling during the period 1987-91, the species rapidly colonized the ditch network sampled (density reaching 61.7 +/- 47.0 individuals/100 m2 and frequency of occurrence around 70-75%) during a 5-year period (1997-2001). Clearance operations probably favoured the expansion of this vulnerable fish species because of positive associations of bitterling with large and deep ditches that had been cleared in the last 2-3 years and characterized by a small cover of submerged plants. Management recommendations are discussed for conserving the bitterling population.