Effects of a Mismatch Between the Water Temperature of Yangtze River and the Specific Requirements of Chinese Sturgeon, Acipenser sinensis

ABSTRACT: The interruption of natural reproduction in the Chinese sturgeon, Acipenser sinensis, is an urgent ecological concern, and the thermal mechanisms underlying its stepped deterioration warrant attention. To systematically elucidate these mechanisms, this study quantified thermal dynamics throughout the reproductive cycle using a multi-scale retrospective analysis of water temperature and historical spawning records. A pronounced, stepwise mismatch between Yangtze River water temperatures and the reproductive requirements of the Chinese sturgeon was identified, manifested as significantly intensified thermal stress and temporal delay. Kernel density estimation (KDE) was used to quantify the thermal requirements for overwintering gonadal development and spawning. Period-stratified statistical tests were then applied to evaluate the alignment between ambient thermal regimes and species-specific requirements. Based on the interdecadal evolution of this mismatch, an intersection analysis between seasonal cooling curves and median spawning temperature was introduced to evaluate synchrony between spawning dates and thermal cues. These analyses revealed that spawning dates passively followed the postponement of the thermal cue, whereas the preferred temperature remained fixed. Collectively, this study demonstrates that thermal mismatches have intensified stepwise through both absolute exceedance of overwintering thresholds and mistimed arrival of suitable spawning temperatures, leading to the sequential degradation of reproduction.