IDENTIFYING PRIORITY SITES FOR THE CONSERVATION OF FRESHWATER FISH BIODIVERSITY IN A MEDITERRANEAN BASIN WITH A HIGH DEGREE OF THREATENED ENDEMICS. Hermoso,

The Guadiana River basin’s freshwater fish species richness and its threatened status in the circum-mediterranean context highlights the need for a large scale study to identify priority areas for their conservation. One of the most common problems in conservation planning is the quantification of a site’s relative value for the conservation of local biodiversity. Here we used a two-tiered assessment approach, which integrates an assessment of biodiversity loss and the evaluation of conservation value through sitespecific measures. These measures based on the reference condition approach introduce the ability to make objective comparisons throughout the Guadiana River basin avoiding a priori target areas. We identified a set of biodiversity priority areas with less perturbed fish communities and that contain rare taxa of special conservation significance because of their outstanding contribution to basin’s biodiversity. The inclusion of complete sub-basins in these biodiversity priority areas ensures the consideration of the main conservation planning principles: representation of all the species and their persistence. Additionally, these areas may guarantee the existence of an optimal solution in terms of spatial aggregation, and cost. However the high fragmentation which the Guadiana River basin is submitted to makes necessary further studies to evaluate the capability of the priority areas pointed out in this work to maintain the Guadiana ́s freshwater fish biodiversity. INTRODUCTION Freshwater ecosystems are among the richest and more diverse ecosystems on earth (Revenga & Mock, 2000) and fish account for a large part of this biodiversity (Saunders