Reservoir to river passage of age‐0+ year fishes, indication of a dispersion pathway for a non‐native species

This study demonstrates passage of age-0+ year individuals of pikeperch Sander lucioperca, common bream Abramis brama and non-native tubenose goby Proterorhinus semilunaris from the Nove Mlýny Reservoir into the River Dyje (Danube River basin, Czech Republic) through the turbine of a hydropower facility. Most fishes had standard length (LS) in the range 12–33 mm. Seasonal patterns corresponded with spawning activity, i.e. an early single spawning event for S. lucioperca, multiple spawning events for A. brama and continuous spawning with a later start and prolonged duration for P. semilunaris. Sander lucioperca, P. semilunaris and larger A. brama (>22 mm) drifted almost exclusively during the dark; smaller A. brama displayed no preference for light or dark. Proterorhinus semilunaris displayed significantly lower mortality than other species when passing through the turbine (3% compared to 18%). The passage of high numbers of P. semilunaris from the reservoir (estimated at 473 000 individuals per year), and their subsequent mass downstream drift, may have contributed to rapid population establishment along the River Dyje and the quick downstream expansion.