Limnetica 33

On 25 April 1998, the tailing pond of the Los Frailes mine in Aznalcollar (Seville, Spain) ruptured, causing one of the most harmful environmental disasters in Europe in recent decades. Through the crack, 6 hm³ of acidic water and metallic mud were spilt, defaunating a large area of the Guadiamar River. After the spill cleanup and habitat restoration, multiple anthropogenic impacts continued to degrade the affected area. This work aimed to provide the most updated list of fish species in the Guadiamar River basin after the spill. Data were collected between 1999 and 2011 by electrofishing, light-traps, minnow-traps and multimesh gill-nests in 78 sampling sites. Species richness values for both native and exotic species in the Guadiamar River basin were high when compared with values for other right bank tributaries of the Guadalquivir River. This may be due to direct contact with the mouth of the Guadalquivir, which allowed the presence of migratory species.  It may also be due to its location in the lower part of the Guadalquivir River basin, where exotic species accumulated. Among the Guadiamar River basin species, Luciobarbus sclateri and Squalius alburnoides have the widest distribution. The former is a generalist species resistant to unfavourable habitat changes, and the latter has a very successful breeding strategy. However, when focused on the affected area, there was a marked increase in exotic species, and both pumpkinseed (Lepomis gibbosus) and carp (Cyprinus carpio) co-dominated together with the native L. sclateri and S. alburnoides. The distribution of species within the river basin suggests that the upper section (except the Agrio reservoir) and middle section tributaries may be acting as native species shelters, while the affected area becomes an exotic species source. This information should be useful for monitoring future changes in the species composition and for management planning measures.