| The naked carp, Gymnocypris przwalskii, is strictly protected by the government of Qinghai province. This fish is the key species for the food chain of Qinghai Lake ecosystem, and plays an irreplaceable role in balance and stability of ecosystem. Due to over fishing and habitat destruction, the natural population of G. przwalskii was sharply declined, and this situation was extremely seriously in the middle of the last century. Some rehabilitation measures for G. przwalskii have been conducted since 1980s. In recent years, it seems that the population of G. przwalskii obviously increased. In this study, we attempted to estimate the abundance and biomass of G. przwalskii by using hydroacoustic technology. This study hopes to provide the basis knowledge for the protection and management of G. przwalskii stock.During the four summer of 2007-2010, the BioSonics DT-X (199 kHz; 210 kHz) and Simrad EY 60 (333 kHz) split beam echo-sounders were used to estimate the abundance and spatial distribution of G. przwalskii in Qinghai. A comparative study was conducted among the two kinds of echo-sounders so as to determine the best analyzing parameters. The main results are as follows:1. The biomasses (95% confidence) of G. przwalskii in Qinghai Lake were 20176.02 (19167.39～21185.01) t,24342.15 (23125.04～255592.58) t,27260.41 (25897.38～28623.42) t and 30120.73 (28798.04～31443.42) t for each August of the year 2007,2008 2009 and 2010, respectively; accordingly the amounts (95% confidence) were 9.26×107 (8.80×107～9.72×107) ind.,1.05×108 (9.98×107～1.10×108) ind.,1.23×108 (1.17×108～1.29×108) ind. and 1.42×108 (1.35×108～1.49×108) ind.; the average density (Min value, Max value) were 1.25±0.41 (0.007, 17.3) ind./1000m3,1.46±0.28 (0.01,19.1) ind./1000m3,1.64±0.23 (0.15,19.96) ind/1000m3 and 1.83±0.36 (0.06,22.89) ind/1000 m3.2. Four time net sampling were located in the Buha River estuary, the Heima River estuary the Erlang Jian and 151 Base, respectively. Statistical analysis, indicated that the average body length and weight of the G. przwalskii in the four times samplings were 275±29.9 mm and 267.9±11.0 g (n=68),267.9±50.7 mm and 263.7±6.9 g (n=54),240.3±38.4 mm and 192.44±13.9 g (n=45),234.7±25.3 mm and 162.2±50.0 g (n=261). It suggested that the size distribution of G. przwalskii was inconsistently in Qinghai Lake, the largest size was at Buha river estuary, and the smallest size was at 151 Bases.3. One-way ANOVA analyzing on fish density among different water layer indicated that, there were significantly difference between the 1～6 m water depth and the other water depth (F=5.521, P<0.05), The G. przwalskii mainly distributes at the 1～6 m water depth. The maximum density (28.08±1.08 ind./1000m3) occurred at the 1～6 m water depth of Quanjihe river estuary, and the minimum density (0.08±0.026 ind./1000m3) occurred at the 21-26 m water depth at the north of Haixin mountain. The horizontal distribution of the fish densities was also inconsistently. The results of the four times surveys indicated that the maximum fish density were 17.3 ind./1000m3 19.1 ind./1000m3,19.96 ind./1000m3 and 22.89 ind./1000m3, respectively. They were located at the Buha river estuary, Quanji river estuary and Erlang jian area. The minimum fish density were 0.007 ind./1000m3,0.01 ind./1000m3,0.15 ind./1000m3 and 0.06 ind./1000m3, respectively, and they were located at the east area of Qinghai Lake.4. Six sampling areas were selected from Qinghai Lake, and the raw data were processed with different parameters in the software Visual Analyzer 4.1 (B1～B4) and Sonar5-Pro (Eo and E1～E4). Variance analysis among fish densities and TS which calculated from two software indicated that there were no significant difference (P=0.524>0.05; P=0.997>0.05). There was significant difference (P=0.020<0.05) among fish density analyzed by the different parameters configuration groups, however there was no significant difference (P=0.926>0.05) among TS. Based on this analysis, we consider that the BioSonics DT-X and EY60 both were applicable for the fish stock assessment in Qinghai Lake. According to the previous studies and technical analysis guides, the parameters configuration B3 and E3 most probably were the best parameters configurations. |
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