Preliminary Hydroacoustic Investigations Of Fishes Stock In Yichang & Yibin Reaches Of The Yangtze River

The target strength of main fishes and cultured Chinese sturgeon (Acipensersinensis Gray) in Yichang reach of the Yangtze River were measured by BiosonicsDT-X Scientific Echosounder(200 kHz) between October 2004 and November 2006.During this period, seven times hydroacoustic surveys on fishes had been taken in the30 km reach from Gezhouba Dam to Gulaobei in the Nature Reserve for A. sinensis inthe Yangtze River with the hydroacoustic equipment. In addition, Yibin reach fromPingshan to Mituo (with 230 km river distance), upstream of the Yangtze River, weresurveyed in April 2006 and January 2007 by using the same echosounder(200 kHz).The main results were as follows:1. The target strength of main fishes value of fishes length 16.0±2.5 cm was—49.5±2.1 dB, 25.1±2.4 cm was—45.5±1.8 dB, 35.1±2.8 cm was—42.9±1.6 dB,45.6±4.2 cm was—40.5±1.1 dB, and 55.0±3.7 cm was—39.8±1.0 dB, respectively.Juvenile Chinese sturgeon total length of 85.50±.5.39 cm, 100.35±5.58 cm,120.78±6.13 cm and 147.92±8.35 cm corresponded with TS value—38.17±1.94 dB,—36.17±1.34 dB,—34.05±2.88 dB and—32.83±2.49 dB, respectively. Theregression equation between TS value and A. sinensis total length was TS=23.295×log₁₀L—82.881.. The target strength of A. sinensis spawners downstream GezhoubaDam in the Yangtze River were from—28.8 to—23.3 dB.2. Fishes distributed inhomogeneously in Yichang reach from Gezhouba Dam toGulaobei, assembling in deep pools but rarely appearing in saults. Mean fishesdensities in the reach from Gezhouba Dam to Aijiahe were obviously higher than thosein the reach from Aijiahe to Gulaobei. In the spawning days of A. sinensis, fishesappeared to congregate in the reach from Gezhou Dam to Miaozui, and the meandensities were 62.62±24.77 ind./1000m³ in 2004, 70.58±37.45 ind./1000m³ in 2005 and132.2±14.7 ind./1000m³ in 2006. The proportion of fishes with the body length from 60mm to 106 mm was higher than other fishes along the reach, approximately over 7.0%of the total fishes. Moreover, the ratios of fishes with body length were less than 53mm and over 750 mm were both all under 2.0%. During the surveys, spawners of A.sinensis were detected. The estimates were 1453 ind. in 2004, 789 ind. In 2005 and734 ind. in 2006, and there amouts with 95% confidence limits were 1370～1537,775～803 and 706～762 ind. respectively. 3. Fishes densities along Yibin reach, upstream the Yangtze River from Pingshanto Mituo, were very low, the average under 15.0 ind./1000m³. Fish targets were likelyhigher close to downstream reach of cities and towns than other reaches. During thesurveyings, signals of large fishes were detected, They were likely Chinese paddlefish(Psephurus gladius), an critical endangered fish.After three years of research, it is primarily established to use hydmacousticmethod to assess fishery resources in the Yangtze River. And it has wide prospects inthe field of inland water for assessing fishery resources and monitoring hydroecologyand its assessment by the further and perfect studies.