River flow intermittence is a natural phenomenon intensified by human activities, such as water abstraction and the effects of climate change. A growing number of rivers are predicted to experience intermittent flows, which may impact the diversity and abundance of freshwater species. Dry riverbeds directly diminish the availability of habitats for freshwater organisms, and suitable environments can turn into ecological traps with reduced survival rates, posing a significant threat to population persistence. Even though fish movements can enable drought-affected populations to persist, little is known about individual fish movement between intermittent and perennial reaches. Here, we study the movement of individual PIT-tagged Italian riffle dace (Telestes muticellus) in an intermittent and perennial river reach before, during and after two severe drying events. A high proportion of fish from the intermittent reach survived the drying riverbed through directed upstream migration. This was manifested in fish living in the intermittent reach of the river displaying significantly higher linear ranges, and net travelled distances during the monitoring period than fish in the perennial reach, which remained resident with limited linear range and net distances travelled. This finding underscores the importance of conserving longitudinal river connectivity in the face of increased water scarcity and intermittent flow patterns.
