Freshwater Biology (2010) 55, 1734–1746 doi:10.1111/j.1365-2427.2010.02407.x Changes in fish assemblages in catchments in north-eastern Spain: biodiversity, conservation status and introduced species ALBERTO MACEDA-VEIGA*, ANTONIO MONLEON-GETINO†, NUNO CAIOLA‡, § FREDERIC CASALS AND ADOLFO DE SOSTOA* *Department of Animal Biology (Vertebrates), University of Barcelona, Spain †Department of Statistics, University of Barcelona, Spain ‡IRTA Aquatic Ecosystems, Spain §Department of Animal Production, University of Lleida, Spain SUMMARY 1. North-eastern Spain is a hot spot for the introduction of alien fish species, and its native fish fauna is one of the most endangered worldwide. We used an extensive data set from 2002 to 2003 and historical information from the area to characterize fish diversity and establish conservation priorities in river catchments. 2. Diversity indices were used to characterize fish diversity at the basin scale. An index of conservation status was applied for each species, which considers the occurrence, abundance and endemicity of each taxon. We used indirect ordination methods to test the relationship among basin features and to identify those variables most correlated with each other. To identify physical, biotic and environmental characteristics that seem to make a basin particularly susceptible to invasion, we performed a step-wise multiple regression to examine the relationship between the number of native, translocated and introduced fish species (including the original native species richness of each basin), and landscape variables. 3. Over a period of approximately 50 years, the mean range size of native fish species has decreased by 60%. The greatest decline occurred in Gasterosteus gymnurus, Anguilla anguilla and Salaria fluviatilis, for which species over 75% of the original distribution area has been lost. The species with the highest conservation index were Gasterosteus gymnurus and Salaria fluviatilis. 4. Basin area and the catchment type explained 70% of variation in native species richness, whereas the number of dams and basin area accounted for more than 80% of variation in the number of introduced species. 5. The original native species richness and the number of introduced species at basin scale were not related, and thus there was no evidence of ‘‘biotic resistance’’ to invasion. The restoration of natural hydrologic processes and the development of specific management tools to protect native species, such as the prioritization of areas for fish conservation and the eradication of local populations of exotic species, are required to restore native fish fauna in these catchments. Keywords: conservation, damming, endangered species, fish diversity, non-indigenous species Correspondence: Maceda-Veiga, Department of Animal Biology (Vertebrates), University of Barcelona, Spain. E-mail: [email protected] 1734 Ó 2010 Blackwell Publishing Ltd Changes in Iberian fish assemblages 1735 Vilizzi, 2005). In some respects, freshwaters can be Introduction considered as ‘‘islands’’ in a sea of land and fresh- Mediterranean streams are among the most endan- water fish are unable to disperse across land and sea gered of ecosystems (Magalha˜es, Ramalho & Collares- (Gido & Brown, 1999). Identifying the factors that Pereira, 2008). The decline of freshwater fish and the make systems more or less invasible has been one of spread of alien species is a complex phenomenon the most important issues in invasion ecology (March- emerging on global, regional and local scales (Apari- etti et al., 2004; Davies et al., 2007a; Fridley et al., 2007). cio et al., 2000; Clavero, Blanco-Garrido & Prenda, From the beginning of the study of ecological inva- 2004; Leprieur et al., 2008). Fish communities are sions (Elton, 1959), many factors have been used to determined by a wide range of physical and biotic predict invasibility in freshwater ecosystems, and the processes and their composition changes over time variables highlighted in most studies are related to and space (Magalha˜es, Batalha & Collares-Pereira, anthropogenic disturbances and the strength of any 2002; Blanchet et al., 2009). A greater understanding of biotic resistance of native communities to invasion the structure of fish communities and the distribution (Fridley et al., 2007; Leprieur et al., 2008; Olden, of species is necessary to establish the conservation Kennard & Pusey, 2008). status of native species, to develop management The decline of freshwater fish species in some strategies and to analyse the spread and introduction Iberian catchments up until 1996 has been assessed, of alien biota (Filipe et al., 2004; Marchetti et al., 2004; although the various hypotheses to explain the Clavero & Garcı´a-Berthou, 2006; Magalha˜es et al., decline have not been tested (Aparicio et al., 2000). 2008). In addition, the conservation status of native species The native ichthyofauna of the Iberian Peninsula is in this region has probably declined further as a result dominated by the Cyprinidae and contains few of new alien species and ineffective management; piscivores (Sostoa et al., 1990; Doadrio, 2001). This indeed, aquatic species are usually not considered in fauna is highly adapted to the harsh climatic condi- protected areas (Aparicio et al., 2000; Filipe et al., tions of the region, in which droughts and floods are 2004). common cyclical phenomena (Magalha˜es et al., 2007). Here, we examined the distribution of freshwater Although such climatic features contribute strongly to fish to establish conservation priorities and to identify the structure of assemblages (Magalha˜es et al., 2002), the species that are most threatened. Our main goals habitat destruction and the introduction of alien were (i) to characterize fish diversity between basins; species are now strongly involved and considered (ii) to compare the spatial distribution of alien and the main threats to native biodiversity worldwide native fish; (iii) to analyse the changes in fish assem- (Aarts, Van Den Brink & Nienhuis, 2004; Marchetti blages over time, comparing the distribution in 2002– et al., 2004; Clavero & Garcı´a-Berthou, 2005; Leprieur 2003 with the original range of native fish species and et al., 2008; Blanchet et al., 2009). (iv) to identify catchment features (land-use, native The introduction of alien species has social, economic fish diversity, hydrological disturbance, habitat pro- and ecological implications. For instance, biological tection, etc.) associated with the number of native and invasions may be the cause of species extinctions introduced fish species present in each basin. (Clavero & Garcı´a-Berthou, 2005), and this phenome- non is particularly worrying in regions with high species richness (of which many are endemic), as is the Methods case in the Iberian Peninsula (Doadrio, 2001). More Study area than 50% of the species in catchments in Catalonia (NE Spain) have been classified as vulnerable, endangered This study was conducted in Catalonia, in the NE of or critically endangered (Doadrio, 2001). Moreover, the Iberian Peninsula, and involved all the rivers this region is considered a ‘‘hot spot’’ for the introduc- between the Muga and Riudecanyes basins (known as tion of alien fish in the Iberian Peninsula. ‘‘inland Catalonian catchments’’ in this region Freshwater fish communities provide excellent because both the source and mouth of these rivers is case-studies for assessing the patterns and conse- in Catalonia), plus parts of the Ebro (Noguera Palla- quences of biological invasions (Copp, Wesley & resa, Noguera Ribagorc¸ana and Segre rivers) and Ó 2010 Blackwell Publishing Ltd, Freshwater Biology, 55, 1734–1746 1736 A. Maceda-Veiga et al. Fig. 1 The mainstems of rivers in Catalonia (NE of Iberian Peninsula, Spain) whose catchments were surveyed. Se`nia basins (Fig. 1). Together, the study area covered CPUE) for all freshwater fish species at the 325 nearly 155 000 km2. The Ebro is the second largest sampling sites surveyed between 2002 and 2003. Fish river in the Iberian Peninsula, and has the highest were caught with a portable electrofishing unit which discharge, followed in the case of Catalonia by the generated up to 400 V and 2 A pulsed D.C and the Llobregat and Ter basins. The other Catalonian basins same equipment was operated across sites. Fish sam- are smaller because they rise in a coastal range of pling was based on a single-pass electric fishing mountains and their valleys slope relatively steeply method, and sites were surveyed in the same season down to the sea. Although most of these rivers follow to provide similar hydrologic conditions (mainly low a typical Mediterranean hydrological regime, with flow) within sampling sites (CEN, 2003). The location of highly variable intra- and interannual discharge, there each sampling site within a reach was selected in the are slight differences between large and small basins. field based on accessibility and representativeness, and The former are characterized by main peak flow in attempts were made to include a variety of habitat spring, as a result of snow melt and rain, and a types (pools, riffles and runs). Sampling effort was secondary peak in autumn caused by rainfall. In uniform among sites, a reach length of approximately contrast, small basins have the highest flow in autumn 100 m being fished, and only relatively shallow reaches and very low flow in summer, often being reduced to (<1 m) were selected to allow for efficient electrofish- a series of isolated pools. In addition to natural ing. Our experience indicated