Limnetica 30

Fish habitat modelling results are strongly influenced by velocity and depth patterns as well as by morphological parameters of the riverbed (i.e., substrate and refuge cover). Studies regarding the use of substrate in habitat modelling are well represented in the literature, whereas the use of cover in such models is commonly neglected because it is difficult to quantify the refuges or the instream areas where fish can hide from predators. However, there is clear evidence that fish habitat use and preferences are associated with refuge cover. Ignoring this variable can lead to incorrect restoration and flow management decisions based on misleading results. To avoid this, river restoration goals should only be set with reference to habitat conditions found at undisturbed sites rather than with the aim of improving habitat heterogeneity. The aim of this study is to compare the habitat availability for two cyprinid fishes, the Southwestern arched-mouth nase (Iberochondrostoma almacai) and the Arade chub (Squalius aradensis), at undisturbed (i.e., near-natural state) and disturbed sites (i.e., sites impacted by agricultural activities that have led to nutrient enrichment, destruction of riparian woodlands, straightening of the river channel and water abstraction). This is done by alternately considering substrate or refuge cover in a weighted usable area (WUA) determination to understand the interactive effects of these morphological variables as well as their influence on habitat availability. Different outcomes were generated by the use of refuge cover and substrate in habitat simulation. The results underline the importance of considering refuge cover in habitat models and also point to the need to take into account minimally disturbed or undisturbed sites within the same river upon developing future management actions.