Comparison of 0+ fish communities between regulated-channelized and floodplain stretches of the River Morava
Jurajda, P.; Reichard, M.; Hohausova, E.; Cerny, J.
Recruitment of 0+ fishes in two lowland stretches (regulated-channelized and floodplain) of the River Morava (Danube basin) was assessed by electrofishing, using the point abundance sampling strategy. Both stretches originally meandered with large floodplains, however, the upper stretch has been extensively channelized resulting in the cessation of flood events and 5 weirs now interrupt the flow of the river. During two years (1995-96), 49 and 37 sites were sampled, respectively, during late summer and 0+ fish communities were evaluated and used to describe reproductive efficiency and recruitment. Changes in the character of spawning sites and nursery areas, after channelization and regulation have affected the 0+ fish community. In both years the total number of 0+ fish species was higher in the floodplain stretch of the river (22 and 16 resp.) compared with the regulated-channelized stretch (18 and 13 resp.). However, the average species richness in all sampled sites was significantly higher in the regulated-channelized stretch during low discharge, although no significant difference was apparent during high discharge. The major component of 0+ fish community in the regulated-channelized stretch comprised of bitterling, bleak, chub and roach in both years. The recruitment of phytophilous species was strongly limited in this stretch of the river at all times, and during high discharge species richness and density of 0+ fish significantly decreased. In the floodplain stretch, bleak and white bream accounted for more than 50 % of the 0+ fish community during low discharge. During the higher spring discharge, ide predominated (77.4 %). The recruitment of lithophilous rheophilic species (e.g. nase, dace, barbel) in the free-flowing floodplain stretch was not markedly higher than in the regulated-channelized stretch. Reproduction of fish in the regulated-channelized stretch of the river with low habitat diversity was more uniform between years when compared to the floodplain stretch which includes a more diverse habitat due to its large floodplain area.