Hydroacoutics Surveys On Biomass Of Gymnocypris Przewalskii Przewalskii In Qinghai Lake

Qinghai Lake is the biggest inland saltwater lake in China. It is located in the north-east of the Qinghai-Tibet Plateau at the altitude of 3195 meters above the sea level. It covers an area of 4456 km~2 and has the water depth of 19 meters on the average, with the salinity being 14‰. It is an oligotrophic lake. Gymnocypris przewalskii przewalskii (Kessler) is the only one commercial important local aquatic animal. It is at the core status of the whole ecological system of Qinghai Lake. Because the lake is in the zone of high elevation and severe cold, and the water temperature rather low, the food organisms in the lake are in paucity. Thus, G przewalskii przewalskii grows very slowly, and has a small brood amount and low survival rate. Since the exploitation in 1958, the biomass decreased rapidly because of imperfect management and the overfishing. At present, G przewalskii przewalskii is in the danger of depletion. Their depletion will not only be the grave loss to the biological diversities and germplasm resources in China, but also will severely destroy the ecological balance of the "coexistence of fishes and birds", resulting to the collapse of the whole ecological system in Qinghai Lake, and ultimately making the lake fall into a dead lake from "the Plateau Pear ". Therefore, the saving of G przewalskii przewalskii is especially important. On the basis of the field hydroacoustic investigation from 2003 to 2005, researches have been made on the biomass of G przewalskii przewalskii. Here are the conclusions: The fish preferred the water under 1.5 meters to surface water layer in Qinghai Lake. Average density of fish in surface layer was much higher than that in middle and bottom layers, and significant difference between the two water layers was observed(T-test, p<0.05). Meanwhile, significant difference in fish densities was also observed horizontal within the 174 statistical units. The spatial variations of horizontal distribution in fish densities in Qinghai Lake was caused mainlyby aggregation activity of fish, water temperature, low density and even distribution. However, no significant correlation was found between the aggregation activity of fish and water depth, or distance from the sampling sites to the shores. The biomass in July 2002, Oct 2002, Aug 2003 and Aug 2004 were estimated to be 814.81, 2377.46, 3105.10 and 5017.69 tons respectively by applying hydroacoustic method. Based on the hydroacoustic studies of G przewalskii przewalskii, some strategies for sustainable utilization of fishery of Qinghai Lake had been put forward from a sustainable development point of view.