Hydrological and water chemical factors in the Yichang reach of the Yangtze River pre- and post-impoundment of the Three Gorges Reservoir: consequences for the Chinese sturgeon Acipenser sinensis spawning population (a perspective)
[Xiao, H.] China Three Gorges Project Corp, Inst Chinese Sturgeon Res, Yichang City 443100, Hubei Province, Peoples R China; [Duan, Z. -H.] Chinese Acad Sci, Inst Hydrobiol, Wuhan, Peoples R China
In order to understand the downstream hydrological and water chemical status after impoundment of the Three Gorges Reservoir (TGR) and to assess the impact of changes on the spawning of Chinese Sturgeon, we assessed hydrological factors (water temperature, water level, water discharge and sediment concentration), and some water chemical factors (dissolved oxygen and ammonia-N) at the Yichang spawning reach during pre- and post-impoundment periods. In addition, hydro-acoustic survey on the occurrence and distribution of Chinese sturgeon were undertaken and investigations on sturgeon-egg-eating predatory fishes were conducted to evaluate the spawning occurrence date of the Chinese sturgeon during autumn between 1997 and 2008. The main subject of interest is whether changes in spawning ground conditions occurred in pre- and post impoundment periods, from 1998 to 2008. After impoundment of TGR, when spawning occurred, many environmental factors decreased from pre-impoundment levels: sediment concentration (down 96.30%), water discharge (down 33.44%), flow velocity (down 12.20%) and water level (down 4.52%). Judging from the annual cycle, annual mean ammonia-N decreased by 50.9%, annual mean dissolved oxygen concentration also decreased by 9.6%. However, some factors increased: monthly average water temperature (increase 7.5% to a mean of 18.7 degrees C) in every Nov after impoundment. The analysis showed that the number of days with suitable water temperature for Chinese sturgeon spawning between Oct and Nov varied according to the highest impoundment level of the TGR. The annual natural spawning activity showed that there were two spawning periods each year from 1997 to 2002 (pre-impoundment period) with the exception of 1998, but there was only one spawning period each year from 2003 to 2008 (post-impoundment period). There was annual average 369 adults in 1998-2002, and there was annual average 231 adults in 2004-2008. There was annual spawning magnitude 3547.5 ten thousand eggs in 1997, and there was only 193.5 ten thousand eggs in 2008. The date for the beginning of spawning was delayed gradually by the impoundment of TGR. The later spawning periods may relate to a change in original water temperature rhythm in the Yichang spawning reach and reaching the upper limit of the spawning temperature in the fall after 2003 may also be the key to regulate occurrence of reproduction and its intensity.
Xiao, H.; Duan, Z. -H..Hydrological and water chemical factors in the Yichang reach of the Yangtze River pre- and post-impoundment of the Three Gorges Reservoir: consequences for the Chinese sturgeon Acipenser sinensis spawning population (a perspective),JOURNAL OF APPLIED ICHTHYOLOGY,2011,27(2):387-393