HYDROACOUSTIC SURVEYS ON TEMPORAL AND SPATIAL DISTRIBUTIONS OF STOCKED CARPS IN THE EAST LAKE

The temporal and spatial distributions of atrificial stocked carps in the East Lake were inverstigated with an echo sounder in 2000. The transducer was set horizontally and vertically to got fish echoes from surface (depth less than 1.5m) and middle bottom (depth from more than 1 5m to the bottom) water layers, respectively. Surveys both for surface and middle bottom water layers were undertaken once monthly along the same route. Statistics on fish densities were carried out separately by dividing the survey route into 114 units, which one unit was 100 meters in length. The fish preferred middle bottom to surface water layer in the East Lake. Average of density fish in middle bottom (0.0474 ind/m3) was much higher than that in surface (0.0069ind/m3), and significant difference between the two water layers was observed (T-test, P0.001). Meanwhile, significantly differences in fish densities were also observed horizontally within the 114 statistical units both in surface (F=1 62,P0.001) and middle bottom (F=2.11,P0.001). The spatial variations of horizontal distribution in fish densities in the East Lake might be caused mainly by aggregation activity of fish, water temperature, and sewage discharge. However, no significant correlation was found between the aggregation activity of fish and water depth, or distances from the sampling sites to the shores.