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Quantifying the mortality of eel in German inland waters

Project

Production processes

This project contributes to the research aim 'Production processes'. Which funding institutions are active for this aim? What are the sub-aims? Take a look:
Production processes


Project code: 2807HS010
Contract period: 01.09.2008 - 30.06.2012
Budget: 352,002 Euro
Purpose of research: Inventory & Assessment

By determining population dynamics of the European eel in an enclosed river system the pro-ject „Quantification of the Mortality of Eels in German Inland Waters” aimed at providing information for the implementation of the Council Regulation (EC) No 1100/2007 for the establishment of measures for the recovery of the stock of European eel. Over a period of 3.5 years the total number of silver eels leaving the Schwentine River was examined and their health condition and migration behavior were investigated. In addition, eel landing and re-stocking data since 1993 as well as eel predation by cormorants since the year 2000 were as-sessed and analyzed. The comparison of observed and modeled silver eel escapement should deliver information about the reliability of the German Eel Model (GEM II), which was the basis for the development of seven out of nine German eel management plans but has not yet been validated by field studies. Observed annual silver eel escapement per hectare was signif-icantly lower than considered for the river basin district Schlei/Trave. Documented annual silver eel catches by professional and recreational fisheries exceeded silver eel escapement by far. Moreover, it was observed that 32.2% of all escaping silver eels died at the trash rack of the hydropower station Raisdorf 2, despite the installation of a surface and a deep bypass. Thus, potential silver eel escapement was further reduced. Dimension and timing of annual silver eel escapement varied strongly. The onset of main escapement in autumn was apparently influenced by river discharge and temperature. Results indicate that a continuous monitoring of these environmental parameters could help predicting escapement events and reducing anthropogenic impacts during silver eel escapement. The study confirms that the GEM II is a suitable tool for the estimation of silver eel escapement from inland waters. However, to achieve realistic results a careful assessment of river specific model input parameters is re-quired. By modeling different management scenarios it could be shown that especially a re-duction of fishing pressure would result in a substantial increase of silver eel escapement. To reach the 40% escapement target in compliance with the EU eel regulation, however, a closure of all fisheries and a massive increase of restocking would be necessary. High prevalences and infection intensities with the swimbladder nematode Anguillicoloides crassus as well as Eel-Virus-European-X (EVEX) infections of a considerable fraction of the Schwentine-eels have to be considered as significantly reducing the spawner quality of successfully escaping silver eels. In addition, investigations regarding the migration behavior of tagged Schwentine silver eels in the Baltic Sea indicated remarkably slow migration speeds. Additional studies are required to clarify whether their behavior is affected by their individual life histories, since all recruitment in the Schwentine system originates from restocking accompanied by anthropogenic translocations over wide distances.

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Subjects

Framework programme

BMEL Frameworkprogramme 2008

Associated projects: Quantifying the mortality of eel in German inland waters

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