Vulnerability Patterns of Freshwater Fish Communities Across European Rivers

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Introduction: Fish species represent 25% of all vertebrates across the globe and are one of the most threatened animal groups. At least 40% of the fish fauna occurs in rivers for part of their life cycle. European rivers are home to more than 600 fish species, while also being some of the most impaired and altered ecosystems. Objective: The objective was to assess the vulnerability of freshwater fish communities in European river basins. Methodology: Using RivTool and the CCM2 database, we developed the River Restoration Units (R2Us), a set of spatial units that takes into account river network functioning and allows a higher spatial discretisation than river basins. We developed RivFish, a database about the presence of native freshwater-dependent fish in 1556 Europeans river basins. For this, we collected data from 77 references and validated synonyms and scientific names for 667 species. We used the latest International Union for Conservation of Nature (IUCN) Red List assessment to define species distributions in European rivers. After intersecting with the R2U layer, we curated and validated species names and spatial occurrence using RivFish. To map the vulnerability of freshwater fish communities, we used the Habitats Directive (HD) and the IUCN datasets. These consider a distinct number of species and assess conservation status differently: the HD evaluated 165 species, while the IUCN evaluated 516 species. The HD data allowed calculating the composite indicator of Conservation Status, whereas the IUCN data enabled calculating the vulnerability index. Results: Both ana-lyses show higher richness in central Europe, particularly in the Danube basin. Spatially, both highlight southern Europe as the area where fish communities have the highest vulnerability. However, the HD analysis also indicates the Danube and the western Atlantic basins as having high vulnerability. The IUCN analysis shows the Anatolian and Mediterranean biogeographical regions as those with the highest vulnerability values. Conclusions: Southern Europe’s higher vulnerability is likely associated with restricted distribution ranges and high levels of endemicity in Mediterranean fish communities. Overall, these findings improve current knowledge and show that input data may be key to effort allocation towards the management and conservation of European freshwater fish communities.