Ecological responses to flow variation inform river dolphin conservation

Many environmental flow studies have relied on state- and rate-based metrics of lower trophic species to build flow-ecology relationships, with limited incorporation of population processes and species traits. Effects of flow on keystone freshwater megafauna remain poorly understood. We incorporated habitat selection traits of the Ganges River dolphin (GRD, Platanista gangetica gangetica), an apex predator, to quantify flow-ecology responses in Nepal’s Karnali River during the low-flow season, defining ecological responses as suitable habitat templates (usable surface area) that support GRD fitness. Using temporally and spatially measured available and occupied habitats, we developed flow-ecology responses. Variation in flow generated substantial differences in ecological responses across time and space, indicating aquatic species adjust among habitats to support life histories. Limited availability of suitable habitats combined with uninformed water regulations likely place GRDs under severe physiological stress during January–April, suggesting reduced flows contribute to endangerment of endemic aquatic biodiversity. Ad hoc flow management is no longer tenable. Quantifying flow-ecology relationships of foundational species, particularly megafauna, is crucial for monitoring water alteration effects and determining minimum flows to maintain healthy, functional freshwater ecosystems in the Anthropocene.