Coocorrência de peixes ao longo de um gradiente longitudinal na bacia do rio Jaguaribe, CE, Brasil

Abstract

Understanding how fish assemblages in rivers are structured has been the subject of many ecological studies, since this knowledge allows us to establish measures of management and conservation of these ecosystems and communities that inhabit them. However, few studies have been conducted on the structuring of assemblies in semiarid rivers. This study evaluated the co-occurrence pattern of fish species along a longitudinal gradient of a semiarid river, identifying the main factors responsible for this pattern. From the hypothesis "in a river located in the Brazilian semiarid region, the longitudinal structuration pattern of fish assemblies will be segregated during the rainy season, since the presence of dams may negatively influence the ichthyofauna dispersion, as well as modify the physical and chemical variables”. Fish were collected from 16 streams during the rainy season, between the years 2014 and 2015. The influence of habitat types and dams on spatial species distribution was identified from null model, using the co-occurrence index (C -score). The combined effect of environmental conditions (turbidity, gravel and flows) and dams was obtained through a Canonical analysis of principal coordinates (CAP). The null model showed a segregated distribution pattern of fish species along the longitudinal gradient. Nevertheless, for the effect of habitats and dams this pattern was random. Partial CAP revealed that the damming and environmental conditions are responsible for the fish species distribution pattern. In conclusion, the fish assemblages of the Jaguaribe River Basin are spatially segregated. Furthermore, the main cause for this pattern is the action of damming, which alters the environmental variables and fragment the upper, middle and lower regions.