Distribución de peces continentales en una cuenca mediterránea altamente perturbadabases ecológicas para la gestión y la conservación

Laburpena

The Guadalquivir River Basin (S Spain) is one of the largest in the Iberian Peninsula and has a remarkable freshwater biodiversity. Although many studies on hydrological regimes or water quality have been conducted in this basin, the biodiversity of freshwater fish as well as their distribution and conservation status have never been globally addressed, as in other Iberian basins. In this context, we synthesized information on freshwater fish using field procedures (285 sampled sites) and other sources of information (bibliographic review, citizen science, historical data). We examined local and regional requirements to study freshwater fish assemblage and occurrence in this highly disturbed basin. Fish distribution patterns at different spatial and temporal scale were analysed, as well as general environmental conditions and the conservation status of the fish community. We documented the presence of 40 species (20 native and 20 exotic) in the basin during the 20th century until today. But we only captured 18 species during the field sampling, with the prevalence for any native species less than 23% (except Luciobarbus sclateri). We report new distribution data on four recently introduced species in this basin: chameleon cichlid (Australoheros facetus Jenyns, 1842), North American black bullhead (Ameiurus melas Rafinesque, 1820), European catfish (Silurus glanis Linnaeus, 1758) and a minnow species of unknown origin (Phoxinus spp.). A compilation of records is used to update the distribution range of these species. The information collected reinforces the evidence on the establishment and expansion of these non-native species. The highest species richness was found in mid reaches, while the lower reaches had very low diversity values. Around 50% of species are threatened, according to the IUCN, several species are declining at an alarming rate and others are probably extinct and/ or their current status is unknown. Human disturbances during the last few decades have caused serious changes in fish distribution and consequently in their conservation status. Hydrological alterations, intensive agriculture and introduced species are probably the principal reasons for the Guadalquivir’s ichthyofauna imperilment. Our study indicates an urgent and real need to identify important areas for fish conservation to guarantee a minimum fish biodiversity conservation over the long term, as well as effective strategies for fish recovery where it still is possible. We also recommend new field sampling to identify the dispersal pathways of the exotic species, especially those recently introduced, and to clarify their current statuses. Historical data sources proved to be a valuable tool for studying long-term changes in fish communities. The comparative analysis of the fish fauna of the Guadalquivir basin between the 19th and 21st centuries revealed an asymmetric process in the extinction of native species and colonization of exotic ones, mainly linked to the natural history of the species and the marked environmental asymmetry and disturbances in the basin. Fish–habitat relationships are a key element for conservation and management strategies, especially in highly disturbed areas where fish communities are subjected to many human pressures. In this regard, multiscale studies help to improve the knowledge of the spatial components and identify local (e.g. water width) and regional (e.g. elevation) key variables in species distribution. Fifteen environmental variables were considered at local scale and twenty at regional level. A total of 18 species captured during field sampling were used for spatial analysis. The global prevalence for introduced species was 25%, which can be considered a high value. The most extended introduced species were eastern mosquitofish (Gambusia holbrooki) and pumpkinseed (Lepomis gibbosus), with around 10% prevalence. Regional and local scales showed different relevance according to the level-study approach (community or species). At the community level, the local, regional and shared components revealed similar influence on the fish assemblage, while at individual species level the local component was the main factor to explain most of fish occurrences. Moreover, variables’ interaction was scarcely selected and almost no introduced species distribution was affected by the interaction of any variable. Our results highlight the poor conservation status of the native fish fauna of the Guadalquivir River Basin as well as the importance of analyzing fish–habitat relationships at different scales and approaches. These results provide useful information to assess and design conservation strategies in Mediterranean-type basin.