Long-term succession of fish biodiversity in the Yellow River Estuary under the influence of water–sediment regime changes

The estuarine reach of the Yellow River (YRE), located within the core zone of the Yellow River Delta Reserve, serves as a critical zone where the conservation and restoration of fish biodiversity constitute essential elements for achieving high-quality development in the Yellow River Basin. However, the fish population in this area is subject to multiple disturbances (especially water‒sediment regime changes), and because of the year-round fishing ban, relevant data are lacking. By integrating historical fish species records with water‒sediment phases classified via Bayesian mutation analysis and key drivers identified via principal component analysis, this study elucidates the reasons for the evolution of fish biodiversity. The results revealed mutation points of the annual runoff (2001) and sediment load (2004) in the YRE during 1950–2023, with a marked declining trend preceding these shifts (P < 0.05), accompanied by fluctuations in fish taxonomic diversity and obvious changes in the dominant fish ecological types. Moreover, the key water–sediment factors influencing fish biodiversity were associated primarily with fish reproduction and migration during the investigation periods, including the proportion of monthly mean discharge relative to the natural baseline phase, minimum daily ecological flow guarantee rate, and annual flow cessation days in zero-flow years. We emphasize that these findings are based on empirical observations from implemented water regulations, but the causal relationship requires rigorous testing via process-based models or controlled experimental studies. Nevertheless, this study still provides the necessary empirical data and initial hypotheses for subsequent research, which can serve as a reference for optimizing protection measures for the YRE.