Abstract
The European eel (Anquilla anquilla) has been declining throughout its area of distribution, is addressed in several pieces of legislation, and is the target of extensive restoration efforts. Therefore, investigating and conserving natural eel habitats is urgently needed. Large, near-natural rivers have become rare in Europe but the Balkans host some of the extant examples. However, several Balkan rivers–among them the transboundary river Vjosa/Aoos of Albania and Greece–are under threat from planned hydropower constructions. This study synthesizes European eel catch data from four institutions and the results of a recent electrofishing survey. Population density and structure as well as habitat choice were studied at different spatial scales. We calculated densities for each meso-habitat (0–1303 ind./ha) and extrapolated these values across three different hydromorphological channel sections (meandering: 70 ind./ha, braided: 131 ind./ha, constrained: 334 ind./ha), resulting in an overall mean density of 168 ind./ha. Proposed hydropower plants would cut off about 80% of the catchment currently accessible and impact river sections downstream of the dams by disturbing hydrological dynamics. By linking study results to relevant legislation and literature we provide evidence-based data for water management decisions. We call for the Vjosa/Aoos to be protected in order to secure its outstanding conservation value.
Highlights
European eels (Anguilla anquilla Linnaeus 1758) exhibit a highly unique catadromous life history cycle
Many authors propose that historically the European eel could access all rivers along the Adriatic and Aegean coasts [10,31]
Most studies only report on the presence of European eels and limited quantifiable data are available
Summary
European eels (Anguilla anquilla Linnaeus 1758) exhibit a highly unique catadromous life history cycle Following their reproduction in the Sargasso Sea (Western Atlantic Ocean), a portion of the larvae (leptocephali) arrive in the Mediterranean Sea on the Continental Shelf after 2–3 years of oceanic migration, covering a distance between 5000 and 10,000 km [1,2,3]. After a second metamorphosis into a sexually mature stage (silver eels), the eels migrate downstream and migrate back to their reproductive grounds in the Sargasso Sea [2] Despite their broad distribution from subarctic environments in the Kola Peninsula and North Cape in northern Europe to subtropical environments in Morocco and the Mediterranean regions of Egypt, they are considered to be one panmictic population, an hypothesis supported by genetic analysis [4,5]. The European Inland Fisheries Advisory Commission (EIFAC) and the International Council for the Exploration of the Sea (ICES) estimated that this noticeable and prolonged decline has left only 10% of the historical European eel population intact [13]
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