ECOLOGICAL AND ENVIRONMENTAL ASSESSMENT INDEX IN THE MIDDLE-LOWER REACHES OF THE YANGTZE RIVER BASED ON THE SPAWNING POPULATION SIZE OF CHINESE STURGEON

The spawning population size of Chinese sturgeon is an important factor affecting the breeding activities. Here we suggest the spawning population size as a key index for the ecological and environmental assessment of the Yangtze River. Basing on the crucial population parameters and historical monitoring data, we determined the reference value and evaluation grade of this index using the theory of regime shift. The spawning population size more than 670 is considered “excellent”, 400—670 is considered “good”, 200—400 is considered “medium”, 50—200 is considered “poor”, and below 50 is considered “extremely poor”. The results of hydroacoustic detection indicate that this index is assessed as “good” before the impoundment of the Three Gorges Reservoir (TGR) (1998—2001), “medium” between the impoundment of the TGR and the Xiangjiaba Reservoir (XBR) (2004—2012) and “extremely poor” after the impoundment of the XBR (2013—2020). To restore the wild population of Chinese sturgeon, it is suggested to repair the function of spawning grounds, to release plenty of mature and big-size individuals, and to establish the national conservation center for Chinese sturgeon.