Fish community and fisheries management of Brno Reservoir following revitalisation measures
2015
Jurajda, Pavel | Adámek, Zdeněk | Valová, Zdenka | Janáč, Michal | Roche, Kevin
Brno Reservoir (259 ha) is one of the most intensively utilised waterbodies in the Czech Republic, being used simultaneously for recreation, sport, fisheries, boating and electric power production. Despite this, no consistent fish survey has yet been performed at the reservoir. Between 2009 and 2012, a number of measures, including fish biomanipulation, were applied to improve water quality. Large cyprinids (mainly common bream Abramis brama) were removed and predatory fish (e.g. pike Esox lucius, zander Sander lucioperca) stocked. In September 2012 and 2013, we carried out an extensive study of the fish community in order to describe the present fish assemblage and evaluate the success of biomanipulation. Fish were sampled at 11 locations using electrofishing (inlet zone) and beach seining (lake zone). Twenty-three species and one hybrid were recorded (inlet zone — 20, lake zone — 14), with roach Rutilus rutilus and bleak Alburnus alburnus (plus perch Perca fluviatilis) dominant in inlet samples, but carp Cyprinus carpio dominant by biomass; and white bream Blicca bjoerkna and roach dominant in the lake zone, both by abundance and biomass. Predatory species represented 14-17 % of biomass in both the inlet and lake zones in both years. The final results of biomanipulation were questionable. While a low proportion of adult bream suggests successful removal, populations of small cyprinids, such as roach and white bream, increased in compensation. There was little evidence for an increase in predatory fish following stocking, probably due to angling pressure. Our results indicate that biomanipulation to improve ecological water quality in reservoirs is unlikely to be successful when they are managed specifically for carp and predator angling.
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