三峡库区澎溪河鱼类时空分布特征的水声学研究

Spatio-temporal distribution of fish in the Pengxi River arm of the Three Gorges reservoir

为了解三峡库区支流澎溪河鱼类时空分布变化,2009—2010年的秋季、冬季和春季,使用Simrad EY60鱼探仪对澎溪河的鱼类资源量及其时空分布特征进行3次声学调查。结果表明:3个季节鱼类水平分布不均匀,鱼类最大密度分别为67.07尾/1000 m3,19.66尾/1000m3,17.25尾/1000m3且不同季节上层、中层鱼类密度水平分布有显著性差异(P≤0.01,P=0.03);各季节鱼类密度垂直分布也有一定差异,冬季上层鱼类密度和下层鱼类密度差异较为显著(P=0.05);另外鱼类密度昼夜分布有显著性差异(P<0.05),造成该现象的原因主要是由于鱼类的昼夜垂直节律(Diel Vertical Migration,DVM)引起;3个季节的鱼类目标强度(TS值)的差异极其显著(P<0.01),其中秋季鱼类TS最高((-57.0±5.6)dB),春季TS值最低((-58.6±4.9)dB),造成该差异的原因是4—6月是长江上游鱼类繁殖季节,仔稚鱼居多。鱼类空间分布及其位点的水深关系分析显示,鱼类密度水平分布秋季、冬季与水深不相关(︱r︱<0.2),春季与水深中度负相关(r=-0.5,P≤0.05)。

The Pengxi River has become an important anabranch of the Three Gorges reservoir following construction of the Three Gorges Dam. The river has the largest submersed area and the most extensive riparian zone of all of the tributaries to the reservoir. Changes to the hydrology of the system are expected to affect both the abundance and distribution of fish fauna and environmental conditions in the Pengxi River. We documented the temporal and spatial distribution of fish in the river by conducting acoustic surveys, using a split-beam echo-sounder （Simrad EY60, 200 kHz）, in autumn （October to November, 2009）, winter （ December 2009 to January 2010）, and spring （April to May, 2010）. During the same period, we also collected samples of the fish assemblage using gill nets and shrimp pots. The acoustic surveys were typically completed during the day, although we also surveyed some sections of the river at night during the winter. We estimated fish density using the echo integral method at three depth strata and in the entire water column several times during each of thethree seasons. The depth strata were classified as surface （from transducer to 1/3 total depth）, mid-depth （1/3 to 2/3 total depth） and bottom （2/3 total depth to the riverbed）. We tested for differences in the distribution of fish throughout the Pengxi River （ horizontally, vertically, day and night, and seasonally） using the survey data. Our results suggest there are significant differences in the spatio-temporal distribution of fish in the impounded section of Pengxi River. For example, the horizontal distribution of fish density was not homogeneous, and varied significantly among seasons within the surface （P ~〈0.01 ） and mid-depth （P= 0.03） water strata, but not among seasons within entire water column （P = 0.70）. The highest density of fishes was found at the confluence of the Pengxi River arm and the main body of the impoundment. The maximum density was 67.07, 19.66, and 17.25 ind./1000 m3 in autumn, winter, and spring, respectively. Within seasons, fish density varied vertically between the surface and bottom strata in winter （ P = O. 05 ） , but not among other depth strata or seasons （0.15 ≤ P≤0.89）. Fish density varied significantly between day and night （P〈0.05） mainly due to diel vertical migration of the fish. The target strength （TS） of the fish varied significantly among seasons （P〈0.01）, with TS highest in autumn （-57.0±5.6）dB and lowest （-58.6±4.9）dB in spring, possibly due to recruitment of juvenile fish. Catch statistics suggest the assemblage was dominated by small fish in all three seasons, which is consistent with the size estimated from the regression equation between mean target strength and length. Furthermore, a large number of fry （body length： 10--15 cm） were released prior to the survey in the spring, likely contributing to the low TS during the subsequent survey. The distribution of fish Was not correlated to the depth of water in autumn and winter （ r 〈0.2 ）, but was moderately and negatively correlated to depth in spring （r=-O. 5,P≤〈O. 05）. However, the pattern of vertical distribution suggests fish were selecting certain depths. In autumn and winter, the fish were most dense between 22-49 m, and 22-44 m, respectively. In contrast, the majority of fish selected depths between 10-dO m in spring. We hypothesize that a number of ecological factors affect the behavior and distribution of fish in this area.