The Feasibility Of Restoration The Chinese Sturgeon (Acipenser Sinensis) Population In The Upper Reaches Of Yangtze River: Macroinvertebrates Surveys And Releasing Trail

The Chinese sturgeon(Acipenser sinensis Gray) is a large anadromous fish,enjoying mandatory protection of the first level in China.The species forages in the near-shore continental shelf regions of East China Sea and Yellow Sea,and spawns in the Yangtze and Pearl Rivers.The Pearl River population is on the verge of extinct almost 10 years. The spawning run of the Yangtze River population was blocked and the population greatly reduced by the construction of Gezhouba Dam in 1981.For the concern of ex-situ conservation of Chinese sturgeon,reintroduction Chinese sturgeon in the upper reaches of Yangtze River is more preponderant than any other artificial environment.The fundamental research of reintroduction need carry out instantly.This study concentrates on the suitability of potential Chinese sturgeon habitat in the upper reaches of Yangtze River,including Three Gorges Reservoir(TGR).Surveys of macroinvertebrates were carried out with a bottom drift D-net and an improved Ekman grab(0.09 m²) in the mainstem of upper reaches of the Yangtze River, including Xinshi-Jiangjin reach(418.5 km),Chongqing-Badong reach(650 km) and Shuifu-Jiangjin reach(340.5 km),from March to December,2008.Community composition,densities and estimation with variable factors were checked preliminarily. The main results showed as bellow:A total of 6686 macroinvertebrates and 29 taxonomic groups,representing 27 families including 28 genera,were recovered from the upper reaches of Yangtze River.6169 individuals came from natural reaches and others were from TGR.Perla,Hydropsyche,Gammaridae and Ephemere were the dominant species of natural reaches,comparing to Mollusca in TGR.Drift varied significantly at the scales of reach,with variation among samples also high.There was clear spatial and temporal variation of macroinvertebrate drift in natural reaches.The number of drifting macroinvertebrates was usually higher in the reaches of Chuanjiang River than reaches of Jinsha River and Minjiang River.Drift densities are higher in spring and lower in winter, reflecting seasonal changes in the life cycles of particular taxa.The mean drift density of natural reaches was 165.50 ind/100·m³ in spring.The higher densities sampling sites happened in the reaches of Chuanjiang River,such as Lizhuang,Nanxi,Dadukou, Huangyi,Baisha and etc.The relationship between current velocity and drift densities was examined.Water velocity had strong support as an important predictor variable and was negatively correlated with drift density(y=511.08e^-0.094x,R²=0.67).In the whole investigation area,Nanxi is the highest density sampling site,with 1810 ind/100·m³ in density and a low water current 0.17 cm/s.On the contrary,the mean drift density of natural reaches is 27.90 ind/100·m³ in winter.Lizhuang,Shenxianqiao,Mituo and etc. happened to be the higher sites.The seasonal dynamics and secondary succession of macroinvertebrates of TGR were possibly regulated by the flowing features,such as seasonal changes in suspended particles,turbidity of the Yangtze River and its seasonal flooding account for the operational pattern of the reservoir.In the present study,the macroinvertebrate community was investigated from Chongqing to Badong.Comparing to natural reaches,reservoir had a much lower density and simpler community structure. The Changshou-Fengdu reach had a higher density at 91.77 ind/m² in average,but the other reach Zhongxian-Fengjie had even no benthos observed.The most abundant sampling sites of TGR happened in Shennongxi Bay with a density at 933 ind/m².Two hundred 7-month-old fish(TL:43.0～64.0 cm,BW:355.0～704.0 g) with external tags and five 3～5-year-old fish(TL:120～138 cm,BW:8.4～20.4 kg) with Vemco ultrasonic transmitters were released in the estuary of Jinsha River in June,2008. Ultrasonic detections and Captured records of tagged-sturgeon showing the distribution and migration were gathered in 90 days.Five 3～5-year-old fish which called big fish, coded as C1～C5,were surgically inserted ultrasonic transmitters two month before releasing.The records showed that ultrasonically fish performed a similar appearance at the releasing moment.Generally,they held position at the releasing place for a while,and then swam upstream or downstream,leaving the releasing place at last.Three big fish,C1, C3 and C4,were believable still stay in Jinsha River,upstream of the Boxi reach.The C5 fish accidently died in Jiang'an reach just six days after releasing(68 km downstream from the releasing point).With a mean speed of 2.64 km/h,the C2 fish swam downstream quickly to Wanzhou reach(712.5 km downstream from the releasing point) of TGR in eleven days.It kept swimming downstream,captured and re-released in Fengjie reach (835.5 km downstream from the releasing point) of TGR five days later.Two hundred 7-month-old fish with external tags,called small fish,had a high capture rate at 17%. They had a wide distribution along the upper reaches of Yangtze River.Captured records concentrated in twenty days after releasing.The small fish got a high speed at 2.72km/h when swimming downstream.The distance ranged 170.3～917km from releasing point to captured reach,619.29km in average.23.53%of the capture records came from natural reaches and the rest were from TGR.The mean body weight of capatured small fish rised of 7.93 per cent,indicating that they started feeding and adapted riverine circumstances gradually.In the early time of releasing,Water current was the main factor infusing tagged fish distribution,and then macroinvertebrates played a key role gradually.Three big fish stayed in the Jinsha River for them adapting riverine circumstances quickly.In conclusion,macroinvertebrates were much more abundant in the upper reaches of Yangtze River(upstream from the end of TGR) than TGR.And macroinvertebrates in main tributaries of TGR were abundant,too.Most released young sturgeon distributed in the upper reaches of Yangtze River and the end of TGR.They maintained healthy body state when captured,which showed that they enjoyed a suitable habitat in the upper reaches of Yangtze River.More research need carry on wheather released sturgeons feed on macroinvertebrates,and wheather the abundance of macroinvertebrates satisfied the growth of Chinese sturgeon.