Daily discharge (first line − solid black line) and air temperature (second line − solid black line) during the three eel downstream migration seasons (in columns). Solid grey lines indicated monthly means over 45 years (flow) and 30 years (air temperature monitored in Bergerac, a station located 40 km from our studied area which has a longer time-series). For river flow, dashed lines represent the average discharge over 45 years long period, and the dotted line represents the 2-year flood.