Impact of the Three Gorges Dam on the spawning stock and natural reproduction of Chinese sturgeon in the Changjiang River,China

Chinese sturgeon(Acipenser sinensis) is the flagship species of the Changjiang River.The migration route of this species is blocked by the first dam,the Gezhou Dam,and its reproduction is affected by the Three Gorges Dam(TGD),one of the largest dams in the world.We studied the impact of the impoundment of the Three Gorges Reservoir(TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013.Results indicate that TGR impoundment has delayed the first spawning dates of the fish from middle-late October to late November,decreased the amount of spawning activities from twice to only once each year,and significantly reduced egg production.In particular,the fish did not demonstrate any spawning activities in 2013.Therefore,TGR impoundment significantly affects the natural reproduction of the fish downstream of the TGD.The spawning stock size of the fish is also predicted to further decrease in the future,which will lead to a risk of population extinction.Ecological regulations must be imposed on decreasing the water temperature to 20℃before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon.

Whole-genome Sequencing Reveals Autooctoploidy in Chinese Sturgeon and Its Evolutionary Trajectories

The order Acipenseriformes,which includes sturgeons and paddlefishes,represents“living fossils”with complex genomes that are good models for understanding whole-genome duplication(WGD)and ploidy evolution in fishes.Here,we sequenced and assembled the first high-quality chromosome-level genome for the complex octoploid Acipenser sinensis(Chinese sturgeon),a critically endangered species that also represents a poorly understood ploidy group in Acipenseriformes.Our results show that A.sinensis is a complex autooctoploid species containing four kinds of octovalents(8n),a hexavalent(6n),two tetravalents(4n),and a divalent(2n).An analysis taking into account delayed rediploidization reveals that the octoploid genome composition of Chinese sturgeon results from two rounds of homologous WGDs,and further provides insights into the timing of its ploidy evolution.This study provides the first octoploid genome resource of Acipenseriformes for understanding ploidy compositions and evolutionary trajectories of polyploid fishes.

CALCULATION OF FLOW FIELD AND ANALYSIS OF SPAWNING SITES FOR CHINESE STURGEON IN THE DOWNSTREAM OF GEZHOUBA DAM

The Chinese sturgeon （Acipenser Sinensis） is one of the unique and important fishery resources in China. Since the construction of the Gezhouba Dam, the traditional migration route of the sturgeon has been blocked; consequently, the length of natural spawning sites is reduced from 800 km in the past to less than 5 km at present. As an endangered species, the Chinese sturgeon has become one of the most conserved aquatic species. In this article, the flow field of its spawning states in the downstream of Gezhouba Dam was simulated and analyzed using N-S equations and k-ε turbulence model. Volume Of Fluid （VOF） method with the Finite Volume Method （FVM） was used to simulate the water-air two-phase flow to examine the computed area. On the basis of the ecological-hydraulic characteristics of Chinese sturgeon, the features of the flow field were investigated to provide theoretical support for the proper management of the Three Gorges Reservoir.

HYDRODYNAMIC CHARACTERISTICS OF CHINESE STURGEON SPAWNING GROUND IN YANGTZE RIVER

Since the construction of the Gezhouba Dam on the Yangtze River in 1981, it has been found that the Chinese Sturgeon, Acipensor sinensis, performs natural propagation annually in a narrow reach downstream close to the Gezhouba Dam site. This might allow one to better investigate the river hydrodynamic conditions of the Chinese Sturgeon spawning ground. In this article, spatial Kinetic Energy Gradient （KEG） and absolute value of vorticity were computed along the river sections from measured data. The relation between Spawn Density per Unit Area （SDUA） and vorticity strength and between SDUA and KEG were worked out. The Results showed that the vorticity and KEG were both effective parameters for describing the hydrodynamic characteristics of Chinese Sturgeon spawning ground. The Chinese Sturgeons prefer to spawn in the river sections where the value of vorticity strength is larger than 0.4 s^-1 and KEG is larger than 0.029 Jkg^-1m^-1.