Just go with the flow? How individual behaviour and river discharge affects silver eel mortality in the river Meuse

No abstracts are to be cited without prior reference to the author.

The European eel, Anguilla anguilla, population shows a strong decline over the past decades. Fisheries and hydropower induced mortality during the downstream migration of silver eels presumably play an important role. River discharge is assumed to play an important role in the onset of migration. This study therefore focuses on the effects of river flow on mortality of downstream migrating silver eel. Furthermore, the impact of individual behaviour on mortality is discussed. To quantify the impact of hydropower and fisheries on silver eel mortality, radio-telemetry experiments were performed in the river Meuse in 2002-2006. A total of 300 silver eels were surgically implanted with Nedap-transponders. This experiment distinguishes between individuals entering the turbine and individuals passing over the adjacent weir. Furthermore, the timing of migration and passage behaviour near detection stations was determined. Mortality rates caused by hydropower stations depended on the number of eel passing the weir/HPS and the water flux through the turbines. Observed behavioral factors, such as hesitation and avoidance of individual eels in front of a hydropower station are discussed. Furthermore, river discharge influences fisheries mortality by affecting the migration route of silver eel in the downstream area. Fishing intensity, and therefore fishery mortality, differs between the routes. The effect of river discharge and individual behaviour