A Habitat Model for Assessing the Impact of the Three Gorges Project on Phytophilic Spawners

Riverine ecosystems provide essential functional habitats for fish reproduction through dynamic hydrological regimes. However, reservoir operations fundamentally alter these natural hydrologic rhythms, creating novel selective pressures on aquatic organisms. This study investigates how dam-induced hydrological changes affect phytophilic spawners (Cyprinus carpio and Carassius auratus) in the Three Gorges Reservoir—a group that has come to dominate the fish assemblage due to the shift from lotic to lentic conditions following impoundment. We developed a process-based habitat model that integrates hydraulic parameters with an innovative water level fluctuation suitability index to quantify functional habitat loss. Our results demonstrate that reservoir drawdown regimes reduce high suitability incubation areas by 39.5% (with WUA decreasing by 34.3%), effectively compressing viable spawning microhabitats into discrete fluvial segments. The altered hydrological conditions create temporal mismatches between embryonic developmental phases and habitat stability windows, disproportionately affecting species with specialized oviposition strategies. These findings provide a basis for ecological regulation to enhance the suitability of spawning habitats.