Longitudinal and temporal water temperature patterns in the Yangtze River and its influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835)

In this study, water temperature longitudinal and temporal patterns were investigated in four locations of the Yangtze River to identify their influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835). The results showed that, historically (1960-1980), the four locations, Pingshan (PS, 2,687river kilometres [rkm]), Yichang (YC, 1,640rkm), Chenglingji (CLJ, 1,265rkm), and Hukou (HK, 805rkm), all had similar average annual water temperatures (around 18.0 degrees C) but very different amplitudes: The upper two locations, PS (11.4-23.2 degrees C) and YC (9.1-25.9 degrees C), were relatively stable and had smaller amplitude than the lower two ones, CLJ (6.0-30.0 degrees C) and HK (5.9-30.8 degrees C). On the basis of the physiological effects for Chinese sturgeon, we defined three water temperature ranges: stressing (>23 degrees C), holding (23-20 degrees C), and spawning (20-16 degrees C). We found that the upper two locations with successful spawning of the Chinese sturgeon (PS and YC) had short or no stressing period but long holding and spawning periods. Currently (2013-2016), the impoundment of the Three Gorges Reservoir increases the time for water temperature decreasing to 20 degrees C at the current spawning ground (YC) in autumn, which increases the stressing and holding periods, and has significant negative impact on the spawning of Chinese sturgeon. Nonetheless, considering the very high stressing temperature and the short duration of the holding and spawning periods at CLJ and HK, we propose that YC is still the most suitable spawning location for the Chinese sturgeon.