Modern state of the Small (Northern) Aral Sea fauna

Abstract

AbstractThe Aral Sea is a terminal lake lying within the deserts of Central Asia in Kazakhstan and Uzbekistan, draining the Amu Darya and Syr Darya rivers. Before the 1960s, it was a large brackish water lake with an average salinity of 10.3 g L−1. The anthropogenic regression and salinization of the Aral Sea at that time resulted from increasing water withdrawals from the Amu Darya and Syr Darya for irrigation purposes. The salinization resulted in the disappearance of most of its invertebrates and all freshwater fish. As a result of the water level decrease, the Aral Sea divided into a northern Small Aral and a southern Large Aral at the end of the 1980s, with the two having different hydrological regimes. After construction the first Kokaral Dam in 1992, the water level of the Small Aral Sea increased by >1 m, with a gradual decline in the salinity beginning. To date, the Small Aral has again become brackish. Its average salinity reached 5.3 g L−1 by April–May 2013, with the highest salinity of 9.9 g L−1 in Butakov Bay, whereas the salinity was very low at 1.2–2.0 g L−1 in the estuary zone of the Syr Darya. There is an ongoing process of restoration of the former biodiversity, with many fresh water and brackish water invertebrate species reappearing due to the decreasing salinity. Freshwater fish species (bream, roach, carp, asp, zander, wels, etc.) returned into the Small Aral from the Syr Darya River and lakes in its lower reaches where they survived. Fisheries are recovering and catches are growing. Continuing salinity decreases, however, may cause decreases in the numbers, or even disappearance, of marine and halophilic invertebrate species. This study summarizes the results of studies of the Small Aral zooplankton, zoobenthos and ichthyofauna carried out in the spring of 2013. An historical review of changes in the Aral Sea and its fauna also is presented.