Temperature effects from hydropeaking impair egg and larval development in Danube salmon <i>Hucho hucho</i> and brown trout <i>Salmo trutta</i>

Hydropeaking is considered an important stressor for salmonids and other species in rivers affected by hydropower. In this study, we investigated the in situ effects of hydropeaking on the survival of eggs and larvae of fall spawning brown trout as well as spring spawning Danube salmon. Egg-to-fry survival of these two species decreased with increasing time of dewatering and desiccation, resulting in temperature effects of overheating and freezing of eggs and larvae. Consequently, mitigation measures should aim for slow ramping rates and sufficient water cover of spawning grounds.