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In order to understand the fish resources and spatial distribution characteristics of the Miyun Reservoir in the waterreceiving area before the South-to-North Water Transfer, the size composition, density and spatial distribution characteristics of the fish in the reservoir area were detected and evaluated by acoustic technology. The hydroacoustic data results showed that the average target intensity of fish was (-46.8±7.6) dB, the fish body length ranged from 3cm to 74.1cm, and the average body length was 10.15 cm.). From the perspective of the entire reservoir area, the average density of fish in the upper water body was 3.3 ind. ∙ 1000m-3, the average density of fish in the middle water body was 570.66 ind. ∙ 1000m-3 and the average density of fish in the lower water body was 20.55 ind.∙1000 m-3. There were very significant differences in the spatial distribution of fish density in different waters (P⪅0.01). The maximum fish density appears in the central waters of the reservoir, which was 865.2 ind.∙1000m-3, and the minimum fish density was 2.87 ind.∙1000m-3 in the waters of the inner lake. The spatial distribution of fish density among different water layers was also extremely uneven (P⪅0. 01). Most fish tend to be distributed in the middle of the water body, with a fish density of 570.66 ind. ∙ 1000m-3. The total number of fish resources in Miyun Reservoir was estimated to be 1.76×108 ind., and the total weight of fish resources was about 3.4×103 t.
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