Habitat suitability modelling at mesohabitat scale and effects of dam operation on the endangered Júcar nase, Parachondrostoma arrigonis (River Cabriel, Spain)

Abstract

Habitat degradation has reduced the complexity of the Mediterranean streams in Spain and contributed to decreasing the historical range of the endangered Júcar nase, Parachondrostoma arrigonis. This species is endemic to the Júcar River Basin (Spain), and most of its populations live in the Cabriel River, which is divided into two segments by the large Contreras Dam. The main objective of this study was to develop a multivariate habitat suitability model (HSM) for this species that can be used to evaluate environmental flows and water management scenarios for the Cabriel River. We first assessed the fish densities (from 2006 to 2008) and compared the habitat characteristics and variability among eight study sites based on the physical characteristics of hydromorphological units (HMUs) or mesohabitats. The abundance of the Júcar nase then was related to the HMU type, and generalized additive models of fish abundance were developed for the sites for both small and large fish. Both models showed acceptable or good performance (adjusted R 2 of 69.4 for small fish and 72.4 for large fish), and fish abundance was used as an indicator of potential habitat quality ['potential nase habitat' (PNH)] for the Júcar nase. The final step was to apply the HSM to evaluate environmentally friendly flow regimens. Hydraulic simulations were used to estimate the PNH under two flow regimen scenarios and in the actual flow regimen for the regulated study site located below the large dam. This article supports the need for new management actions in the Cabriel River, such as implementation of an environmental flow regimen, and illustrates a procedure for the practical application of habitat selection models at the mesohabitat scale.