Redd dewatering effects on hatching and larval survival of the robust redhorse

Abstract

Riverine habitats have been altered and fragmented from hydroelectric dams and change spatially and temporally with hydropower flow releases. Hydropeaking flow regimes for electrical power production inundate areas that create temporary suitable habitat for fish that may be rapidly drained. Robust redhorse Moxostoma robustum , an imperiled, rare fish species, uses such temporary habitats to spawn, but when power generation ceases, these areas are dewatered until the next pulse of water is released. We experimentally simulated the effects of dewatering periods on the survival of robust redhorse eggs and larvae in the laboratory. Robust redhorse eggs were placed in gravel in eyeing-hatching jars (three jars per treatment) and subjected to one of four dewatering periods (6, 12, 24 and 48 h), followed by 12 h of inundation for each treatment, and a control treatment was never dewatered. Egg desiccation was observed in some eggs in the 24- and 48-h treatments after one dewatering period. For all treatments except the control, the subsequent dewatering period after eggs hatched was lethal. Larval emergence for the control treatment was observed on day 5 post-hatching and continued until the end of the experiment (day 21). Larval survival was significantly different between the control and all dewatering treatments for individuals in the gravel. These findings support the need for hydropower facilities to set minimum flows to maintain inundation of spawning areas for robust redhorse and other species to reduce dewatering mortality.