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Escape from the North Sea: the possibilities for pikeperch (Sander lucioperca L. 1758) to re-enter the Rhine and Meuse estuary via the Haringvlietdam, as revealed by telemetry

Brevé, N. W. P., Vis, H., Breukelaar, A. W.
Journal of coastal conservation 2019 v.23 no.1 pp. 239-252
Sander lucioperca, acoustics, estuaries, freshwater fish, lakes, lowlands, salinity, salt tolerance, searching behavior, telemetry, transponders, North Sea
The Haringvlietdam tidal barrier was erected in 1971 between the North Sea and the estuary of Rivers Rhine and Meuse (i.e. Lake Haringvliet). The mega structure safeguards the Dutch lowlands against flooding but also hampers fish migrations. Moreover, the sluices wash out on average 1000–2000 kg of freshwater fish per day. Previous studies showed that these fish die, but we suggested that under certain conditions salt tolerant fish like pikeperch can survive and re-enter the estuary. Fifty pikeperch (Sander lucioperca L. 1758) of over 42 cm LT were surgically implanted with VEMCO acoustic transmitters and 17 with transponders for the NEDAP Trail system®. The pikeperch were released in four batches at the seaside of the Haringvlietdam between January 18 and March 17, 2017. The pikeperch displayed searching behaviour at the sluices but were unable to swim against the strong currents. Nevertheless, two pikeperch re-entered Lake Haringvliet via the nearby ship-lock and nine used the fish-culverts that are integrated in pillars of the Haringvlietdam. It was concluded that at river discharges less than 2000 m3/s (which occurs 50% of the time) the chances of re-entrance are slim but increase with higher discharges causing lowered salinities behind the Haringvlietdam. Based upon the results we conclude that many fish could have been saved the past 45 years by optimizing the management of the ship-lock and fish-culverts and by decreasing the flow velocities in the discharge-sluices. We recommend implementing these options in the planned new management of the Haringvlietdam.