Movements and habitat use by pikeperch (Stizostedion lucioperca (L.)) in a hydropeaking reservoir

We used radio telemetry to measure the habitat use and movements of 20 tagged pikeperch (44-59 cm) in the hydropeaking Pyhakoski Reservoir, Finland, during June 1999-2000. The hydrological conditions in the 8-km-long reservoir were measured and then modeled over eight discharge rates between 30 and 700 m(3).s(-1) . Pikeperch preferred relatively low water velocities and deep water depths especially during the winter. During the summer, pikeperch moved actively in different parts of the reservoir. No relationship was found between hydroelectric plant operations and distances moved by pikeperch during the summer. Movements peaked in autumn but decreased during the winter to a restricted area. After 1 year of monitoring, 4 out of 20 tagged pikeperch remained in the Pyhakoski Reservoir, three had died when descending from hydroelectric dams, 10 had descended downstream to other reservoirs or sea, two were captured by local fishermen, and one fish's signal was lost for unknown reasons.