Factors challenging the European eel (Anguilla anguilla) Stock recovery in continental waters

• Main Author: Prigge, Enno
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Anguilla anguilla
• Online Access: https://oceanrep.geomar.de/id/eprint/19991/; https://oceanrep.geomar.de/id/eprint/19991/1/diss_prigge.pdf; https://macau.uni-kiel.de/receive/diss_mods_00011163

In the present thesis, it was for the first time possible to directly assess the entire silver eel escapement from a medium freshwater system in Northern Germany (Schwentine river system) over a 3-year period (Chapter I). The rare possibility to document the complete escapement of silver eels out of the system and the complete recruitment (via stocking) to the system, allowed for the characterization of factors acting on the amount of emigrating spawners. Thereby, it was possible to document the potential of the Schwentine river system to produce (healthy) silver eels and compare the results with the escapement requirements of the EU Regulation. It became obvious that current estimates of the silver eel escapement from a freshwater system in Northern Germany are overstated. Such an overestimation will have severe consequences for the future development of the European eel stock, because it might lead to a false-positive evaluation of the management success. As it is usually not possible to directly assess the entire silver eel escapement from a freshwater system, scientists across Europe rely on population dynamics models to describe the spawner output. To evaluate the accuracy of such model-approaches, it is of high importance to assess how close to reality the model output actually is. Comparing modeled escapement numbers with the directly assessed in situ silver eel output provides possibly the best evaluation of the model potential. In Chapter II, the German Eel Model II (GEM II), applied in the German EMP, was used to estimate the potential silver eel output of the Schwentine river system. To do so, it was first necessary to adjust the GEM II for the system-specific population characteristics of the Schwentine river eel population. Estimated escapement numbers were in the same range of the actually documented escapement in Chapter I. Results, thereby, document the potential of the GEM II in providing the necessary base for sound management decisions. At the same time, however, Chapter II illustrates the ...