THE EFFICIENCY OF A NATURE-LIKE BYPASS CHANNEL FOR PIKE-PERCH (STIZOSTEDION-LUCIOPERCA) IN THE MARCHFELDKANALSYSTEM

This radio telemetry study is part of a large interdisciplinary resear ch program on the colonisation and development of the Marchfeldkanal(M FK)-system, a man made channel. The immigration of fishes into the MFK is dependent on the effectiveness of fish bypass channels at several weirs. To investigate the efficiency of the lower most fishway we esti mated the population densities along the MFK-system and below the weir s using electrofishing. In addition, the movements of 15 radio-tagged pike-perch at the fishway were observed. Although more than 57 000 fis hes of 35 species passed the bypass channel, pike-perch (Stizostedion lucioperca) were under-represented in the :fishway traps compared to t heir occurrence in the channel. The average daily movement of radio-ta gged pike-perch was 108 m (range 6-333 m) and the maximum observed dai ly movement was 1050 m. The entrance to the bypass channel (280 m belo w the weir, and 100 m above the release site) was approached a number of times by 6 tagged fish, though none of them entered the bypass chan nel during the period of tracking. We conclude that although pike-perc h migrate actively they do not utilise the bypass channel as much as m ost fish species of the MFK. Therefore the weir still represents a bot tleneck for the immigration of pike-perch into the MFK.