The impact on fish stocks of river regulation in Central Asia and Kazakhstan

Fisheries in arid countries of Central Asia and in Kazakhstan have a relatively short tradition of less than 100 years. However, during this period, water resources, originating largely from snow and icemelt, have been subject to large-scale engineering interference required by the growing demands f...
Ausführliche Beschreibung

Fisheries in arid countries of Central Asia and in Kazakhstan have a relatively short tradition of less than 100 years. However, during this period, water resources, originating largely from snow and icemelt, have been subject to large-scale engineering interference required by the growing demands for the expansion of irrigated agriculture. Storage and diversion of flow into irrigation systems have affected original fish stocks through changes in river discharges, blockage of migratory pathways by dams and barrages, increase in dissolved salt content and agrochemicals in drainage waters. In order to boost the indigenous fish stocks, which often give poor yields, fishery managers transferred a number of fish species from other parts of Asia within the ex-Soviet Union. In order to improve the food base for such fish, fish food organisms such as mysids, gammarids and molluscs were also transferred. The introductions often increased fish yields only temporarily or interfered with the indigenous stocks. In addition to valuable fish species, unwanted fish were sometimes brought in. Where river basins became interconnected through canals, fish faunas of these basins intermingled through immigration of species. The new fish communities now form a mixture of indigenous and introduced fish, where one can rarely assume that a balanced state has been achieved. The priority of the governments remains the use of water for irrigation and hydropower production, which leaves fishery managers in the unenviable position of adjusting the management to the continuously changing situation, which is often unpredictable. In order to increase fish production present government strategies focus on the rehabilitation of rivers and terminal lakes with the aim of arresting and reversing the process of salinization of waters and of maintaining water level in lakes. This allows fishery managers to develop strategies for optimizing fish yields under more stable conditions. With the new efforts to revitalize the Aral Sea, the large artificial terminal lakes established from drainage and wash waters, will become of minor importance for fisheries, as their salinity will increase beyond the tolerance level of most fish. However, in freshwater reservoirs and lakes, including those formed from seepage in depressions near irrigation canals, there is considerable potential for raising fish yields. Culture-enhanced methodologies, when introduced, should also lead to substantial increases in fish production from these water bodies. Ausführliche Beschreibung