Evaluating the ecological effects of daily hydropeaking on lithophilous fish spawning habitat in a large mountainous...

Water-level fluctuations caused by hydropower operations have the strongest effects in littoral zones, where they interfere with fish reproduction. Lithophilous species, which adhere eggs to gravel surfaces in these littoral zones, face heightened mortality as hydropeaking alternately inundates and exposes their spawning substrates. However, quantitative evidence connecting the intensity of hydropeaking with ecological impact of freshwater fish is still limited. This study addresses this knowledge gap by quantifying hatching success in fishes under daily hydropeaking conditions.Field experiments were conducted to determine the effect of dehydration duration on egg-hatching success, followed by the development of a water-level-fluctuation-based method to evaluate adhesive-egg spawning grounds and identify ecological thresholds for reservoir operation. Based on the effect of dewatering on fertilized egg survival, 6-h continuous exposure was identified as the ecological threshold for air-exposure-induced egg mortality. The spawning-ground deactivation rate was then proposed, defined as the ratio of the deactivated area (≥6 h exposure) to the total potential spawning area. Finally, it is recommended that discharge variations during the reproductive period be limited to ≤2600 m³ s^-1 and water-level fluctuations be restricted to <1.5 m, to ensure that the majority of spawning grounds maintain intact ecological functions. The study elucidates the ecological mechanisms governing lithophilous fish egg hatching under daily hydropeaking and proposes ecological thresholds for reservoir operation. Furthermore, it provides a quantitative framework for assessing how hydropeaking affects lithophilous spawning habitats.