The Effect Of Water Temperature Process On Natural Reproduction Of Chinese Sturgeon

As a consequence of loss of habitat and human activities, the natural population of Chinese sturgeon has kept decreasing sharply. The interception and impoundment of the Three Gorges Reservoir has caused great changes to hydrological condition of the spawning grounds of Chinese sturgeon, especially the water temperature progress, which has significantly delayed. Based on historical observation data, Chinese sturgeon spawning activities were mainly concentrated in mid to late October and November, but showed a obvious trend of delay in recent years, to explore whether this trend was caused by the changes of water temperature process in the spawning grounds has got very important theoretically to the protection of Chinese sturgeon.In studies on the other sturgeons, high temperature, low temperature, the duration of different temperature, the variation, the changing rate and all the related parameters with water temperature process play different functional roles in gonad development of sturgeons and have different potential effect on eventual reproduction time. On the basis of these studies, this paper puts forward a hypothesis: there is a water temperature process with certain characteristics is the initiation factor of Chinese sturgeon spawning, called “the key water temperature process” which induces the eventual gonad maturation and determines the reproduction date of Chinese sturgeon in natural conditions. With this hypothesis as the theoretical basis, this paper analyzed the related observed data of Chinese sturgeon natural reproduction from 1981 to 2012 and carried on a few researches in the following three aspects:1. Multivariate sequential clustering analysis was introduced to improve the limitation of traditional change-point detecting technology on identifying asynchrony change in cycles of periodic hydrological time series and the concept of structural changing point in hydrological time series was proposed. The variation of water temperature in spawning grounds below the Gezhou dam from 1981 to 2012 was analyzed and it was indicated that the average annual water temperature had a steadily and significantly increasing trend during studying period, while since 2005, the structure of water temperature cycles had significantly mutated, the mutation showed that, after 2005, in annual warming months(from March to June), water temperature has significantly reduced, the lowest-temperature month has also changed, and in annual cooling months(from September to February the next year), water temperature had obviously increased.2. A time series decomposition model based on translation theory was developed, and with this model the water temperature hysteresis effect of Three Gorges dam on the lower reaches during 1982 ~ 2011 was evaluated quantitatively and systematically. The results showed that the water temperature hysteresis effect generated around 2003, after 2003 the water temperature cycles significantly lagged, and longer and longer. In the year 2011, the lag time of water temperature cycle was as long as a month.3. Through the similarity matching technology, the key water temperature process of different length was used to simulate the natural reproduction time of Chinese sturgeon in the past 30 years. As a consequence, the simulation results showed that: when the length of the process reached 14 days, the simulation error got almost constant and the error didn’t increase as the training length grew, which implies that the assumed key water temperature process doesn’t exist. It is concluded that the key factor leading to the Chinese sturgeon natural reproduction time to delay is the lag of the annual water temperature cycle.