Determinants of large-scale spatial distribution and seasonal microhabitat selection patterns of the endangered freshwater blenny Salaria fluviatilis in the Ebro River basin, Spain

Abstract

The freshwater blenny Salaria fluviatilis is an endangered fish species with populations that are in rapid decline, largely owing to habitat degradation caused by human activity. This situation highlights the urgent need to develop measures for the conservation and recovery of the species based on a deep understanding of its specific habitat requirements. 2. In this study, spatial distribution and habitat selection patterns were investigated to determine the limiting factors for the species at different times of the year and at different spatial scales, from macro to microhabitats. 3. The presence of the freshwater blenny was assessed at 127 sites in the Ebro River basin, Spain, between 2002 and 2012. It was only detected at 25 sites, corresponding to the intermediate and lower reaches of medium-sized tributaries and in the main river, in accordance with the ecology of the species. Whether the species was present depended on the physicochemical, habitat and biological conditions of the study sites. Freshwater blenny was very sensitive to organic pollution and eutrophication, the deterioration of substrate composition and channel structure, and the degradation of aquatic and riparian vegetation. 4. Freshwater blenny showed a selective use of microhabitat locations with high current velocity, linked to gravel or cobble substrate. It was also observed that the species is capable of adapting its selection behaviour to the flow-mediated seasonal changes in its physical environment. 5. Although the results presented indicate that the species is not a microhabitat specialist, individual survival is likely to be dependent on the availability of key microhabitats, which must be protected against detrimental human activity.