In total there are 603 species of freshwater fishes recognized within European river catchments (including non-natives, and as yet undescribed species). All described freshwater fish species native to Europe recognised at the start of the project were included, with some additional assessments added later following taxonomic changes. This resulted in 531 species being assessed, of which seven species that are of marginal occurrence in Europe were considered in this assessment, but were classed as Not Applicable. Taxonomy largely follows Kottelat and Freyhof (2007).
For every freshwater fish species native to Europe or naturalised before AD 1500, the following data were compiled:
All species had their global status assessed according to the 2001 IUCN Red List Categories and Criteria: Version 3.1.
The status of species endemic to the Mediterranean basin is based on evaluations made during an IUCN workshop held in Malaga (Spain) in December 2004. All European Sturgeons were assessed at a workshop held in Wuhan (China), at the 6th International Symposium on Sturgeon in October 2009.
The status of all other European species was evaluated when preparing the Handbook of European Freshwater Fishes (Kottelat and Freyhof 2007) during an IUCN workshop held in Berlin (Germany) in December 2006, in coordination with the IUCN Freshwater Biodiversity Assessment Unit. Following these meetings, the assessments were reviewed once again and adjustments were made. All species which are found in the 27 Member States of the EU were re-assessed by the primary assessors and evaluators for their regional conservation status in 2010 via email exchange.
As part of these assessments the population trend status for each species was considered. Due to a lack of centralized monitoring data for most species of freshwater fish, this status is largely qualitatively and not quantitatively determined, with a high level of uncertainty. This is reflected in the high number of species with an Unknown population trend.
Following the review workshops and the uncertainty discussion, the data were edited, and outstanding questions were resolved through communications with the experts and members of relevant Species Survival Commission Specialist Groups (e.g. Salmon Specialist Group).
Consistency in the use of IUCN Criteria was checked by IUCN staff from the IUCN Red List Unit. The resulting finalised IUCN Red List assessments are a product of scientific consensus concerning species status and are backed by relevant literature and data sources.