Abstract :
[en] The fitness of restocked European eel (Anguilla anguilla), an endangered fish species, was studied in relation to
the environmental variables of habitats in six upland rivers that are typologically different in terms of their
hydromorphological and physicochemical characteristics, food resources and fish communities. These rivers received
a total of 76,370 imported glass eels in 2017. During a three-year period, we monitored eels with respect
to total length, annual growth rate, condition factor and density using capture-mark-recapture experiments to
understand the effects of the characteristics of receiving rivers on restocking success levels. Our results showed
the survival of the restocked eels in the six rivers and revealed significant differences between them in terms
of total length, condition factor and density. Better performance in eel yield variableswas observed in a eutrophic
alkaline river with greater roughness of riverbed substrates, dominant pool- and riffle-type flowfacies and lower
brown trout density. The variables conductivity and total hardness had higher explanatory power and were
strongly associated with increased eel density. This study suggests that a well-selected habitat/river in a
restocking programme can be beneficial for the species and recommends restocking practice as a management
tool to achieve eel conservation goals.
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