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Session C5: Downstream Migration of Silver Eel (Anguilla Anguilla) in the River Meuse in the Netherlands 2008 – 2012

Abstract: Downstream migration of European silver eel (Anguilla anguilla) was studied in the Meuse in the Netherlands, in the period 2008-2012. Silver eel (n = 840), with implanted NEDAP transponders, were released at different locations, in the lower part of the Meuse in Belgium (Berwijn at Moelingen) and in the upper part of the Meuse in the Netherlands (Ohé en Laak). Fish were tracked by telemetry at 41 fixed NEDAP Trail detection stations distributed along the Meuse from the confluence with the Berwijn to the North sea, a distance of more than 330 km. Over the period 2008- 2013 75% (n = 630) of the eels were detected. Eel numbers reaching the North sea varied between 6-10% yearly. Most eels migrated to sea by way of the Haringvliet. Silver eel migration showed much individual variation, with fish reaching the sea within several days after being released and fish postponing their downstream migration for more than one year. The onset of migration was stimulated by increasing river discharge. Fish from different maturation classes showed no significant differences in migration speeds. Average individual migrations speed ranged from 0,3 to 1,6 m/s, indicative for at least a partly active migration (average river flow being 1 m/s). Generally migration speed slowed when fish approached sluices and weirs in the Meuse. The influence of the hydro power station (HPS) Linne on the migration was examined. Mortality of silver eel per kilometre, over the river stretch Linne – Lith (130 km) turned out to be twice as high after fish had passed the HPS (0,43% versus 0,22% passing the weir at the same location).
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