The Decline of Threatened Large River Turtle Populations due to Hydrological Regulation: A Conceptual and Mathematical Analysis With Case Studies

Source abstract

ABSTRACT Large river turtles are among the most threatened freshwater vertebrates, with dam construction emerging as an important driver of sustained population decline. This paper develops a conceptual mathematical framework intended to formalize the principal ecological mechanisms linking hydrological alteration and population persistence, illustrated using three representative examples: Cyclanorbis elegans in the Volta River system, Rafetus swinhoei in the Da River and Chitra chitra in northern Thailand. We model population dynamics as a function of nesting habitat availability, hydrological stability and recruitment success, incorporating dam‐induced fluctuations in water levels and seasonal mismatches. Results from the model demonstrate that increases in water‐level variance can push populations below a critical reproductive threshold, leading to rapid extirpation. Empirical observations from the illustrative examples align with model predictions: loss of exposed sandbanks, nest inundation and disruption of reproductive timing are primary drivers, while secondary factors such as temperature and sediment changes play smaller roles. The framework predicts nonlinear tipping points, where incremental hydrological change yields disproportionate demographic effects. Conservation implications include the need for environmental‐flow regimes, protection of artificial nesting habitats and basin‐scale planning. Our findings provide a mechanistic framework suggesting that hydrological alteration may represent one of the principal drivers of population decline in regulated river systems and may therefore deserve priority consideration in conservation planning.