Effects of Exploitation, Introductions, and Eutrophication on Percids in Lake Balaton

Percid populations in Lake Balaton have undergone changes which are considered to have been caused by individual or combined effects of overfishing, interspecific competition from nonnative species, and loadings of nutrients and pesticides. Eurasian perch (Perca fluviatilis) has almost disappeared and the ruffe (Gymnocephalus cernua) population is declining, probably as a result of competition from the eel (Anguilla anguilla) and effects of cultural eutrophication. Growth rate of pikeperch (Stizostedion lucioperca) is declining while that of the bream (Abramis brama) is increasing. Production of cyprinids has increased up to 10% in recent years, apparently in response to accelerated eutrophication. The exploitation rate of pikeperch is far in excess of that considered necessary for maximum sustained yield. The environment in the most eutrophic part of the lake is now considered to be unfavourable for pikeperch. Key words: Percidae, Stizostedion, Perca, Gymnocephalus, exploitation, eutrophication, introductions, ruffe, Lake Balaton