Defining critical habitat conditions for the conservation of three endemic and endangered cyprinids in a Mediterranean intermittent river before the onset of drought

Abstract

Abstract Identifying key factors in species' habitat requirements can be of use in defining critical habitats for their conservation, as well as in assisting the prioritization of habitat restoration actions. So far, most studies on habitat use by freshwater fishes have been focused on widespread and economically important species (e.g. salmonids). This study aimed to identify the early summer habitat use (i.e. before the start of the drought period) of three endemic and endangered Greek cyprinids – the Evrotas chub Squalius keadicus, the Spartian minnowroach Tropidophoxinellus spartiaticus and the Evrotas minnow Pelasgus laconicus, with regard to depth, water velocity, substrate and macrophyte cover. In the case of the chub, habitat use by juvenile and adult fish was assessed separately. Data were collected for each fish group from four habitat types (riffles, runs, glides, pools) by using a modified point‐abundance sampling with an electrofishing device. In total, 120 sampling points were sampled, in two near‐reference perennial reaches of the Evrotas River (southern Greece) in early summer 2014, when there was continuous flow and full connectivity between habitats. All three target species had their highest densities in deeper habitats with low water velocities and depositional substrates such as pools and runs. A high overlap in habitat use was evident for the three species. Habitat use curves based on microhabitat data were created for all species. Μinnowroaches, minnows and large chubs actively selected deep habitats. Minnowroaches and minnows favoured slow‐flowing, vegetated habitats with fine substrate located close to the river bank, while chubs had no clear affinity for particular velocities or substrate types. However, size class comparisons in chub indicated differences in both water depth and velocity. Overall, the results of this study provide the first detailed report of the habitat use of these endangered fish species. These patterns of habitat use highlight the importance of deep habitats that must be preserved as refugia while the drought events progress.