Is the distribution of potamodromous and native Iberian fish affected by artificial barriers?

Connectivity, when addressing freshwater fish species has to be thought as a longitudinal dimension problem. The breach of this dimension by the construction of barriers, such as dams and weirs, is considered to have a deleterious effect on fish population worldwide. This is clearly evident for diadromous, long migrant, species. But, this is still unproven for the typical native species of Iberian freshwater systems. This work addresses the impact of transversal barriers on the distribution of potamodromous and native fish species from three western Iberian river basins. Empirical data from 196 sites was analysed using four different generalized linear models (GLM) approaches designed for quantifying the contribution of connectivity-based variables on species occurrence. The results point towards a non-influence of barriers to longitudinal connectivity on potamodromous and on resident native fish species’ distributions. Environment and pressures, other than connectivity, surpass the individual effect of connectivity infringement. Therefore, a new archetype of the impact of isolation through barriers on fish species has to be developed. A more directed experimental design will be needed to allow a comprehensive understanding of barriers’ effects on potamodromous and native Iberian freshwater fish species.