Boundaries

The Aral Sea Drainages ecoregion lies in the countries of Kazakhstan, Uzbekistan, and Turkmenistan. The ecoregion comprises the remnants of the former Aral Sea, including the Large Aral (or so-called Bol’shoy Aral in the southern part of the former sea where the Amu Darya River flowed), and adjacent deserted land. It excludes the Small Aral (Maly Aral) that belongs to the Lower and Middle Sry Darya [629] ecoregion.

The ecoregion’s western boundary is shared with the Turan Plain [450] along the spurs of the Ust-Urt [Ustyurt] Plateau and Assake-Audan Depression. The Sarakamysh [Sariqamish Kuli = Sarygamysh Koli] Depression (now a lake) is included in the ecoregion. The southern boundary crosses the former delta of Amu Darya south of Urgench and extends eastward to the Mynbulak Depression. Then it rounds the Bukantau Mountains and is contiguous with the Lower and Middle Syr Darya [626] ecoregion along the entire lower course of the Syr Darya River. This ecoregion also includes the waterless area between the lower Syr Darya and the Irgiz-Turgay area [601] - Peski Priaral’skiy Karakumy [Aral Mangy Qaraqumy], Peski Malyye Barsuki Desert, and Peski Bol’shiye Barsuki Desert [Ulken Borsyq Qumi]. The border shared with the Volga-Ural [410] ecoregion runs along the Chagray [Shaghyray Ustirti] Plateau.

Topography

The Aral Sea (63,915 km²) comprises lakes of tectonic origin, and includes many islands. The largest of these are Kug-Aral, Vozrozhdemiya,  Barsa-Kel’mes, and Takmak-Ata. The northern coast of the sea is indented by large bays. The western coast is straight with steep spurs up to 190 m high. The eastern coast is sandy and low, indented by numerous narrow bays, bights, and inlets. The southern coast is formed by the Amu Darya delta, a low alluvial plain with numerous intermittent lakes, channels, and anabranches.

Freshwater habitats

Before anthropogenic desiccation and salinization, the Aral Sea was brackish, with average salinity between 8-10 g/l. It was a large shallow lake that was rich in silt and organic matter, and had a relatively high water temperature. It was also heavily vegetated along most coasts; for example, widespread and well-developed wetlands once occurred along the southern and southeastern coast connecting the deltaic areas of Syr and Amu.

Today, fresh or brackish water habitats have almost completely disappeared. Lake Sarakamysh, which now receives water from the lower Amu Darya, may be considered as a slight substitution of the sea. It, however, is heavily polluted by agriculture wastes, and fishes may contain dangerous amounts of pollutants in their tissues.

Terrestrial habitats

This ecoregion crosses the Central Asian northern and southern deserts, as well as Kazakh semi-desert. The southern desert is distinguished from the northern desert by a greater diversity of ephemeroids (e.g. Eremurus spp. and Rheum spp.) and ephemers (e.g. Bromus spp. and Malcolmia spp.). The Kazakh semi-desert in the northern part of the ecoregion is dominated by bunch grasses such as kovylok (Stipa lessingiana), tyrsik (Stipa sareptana), and tipchak (Festuca valesiaca).

Along the floodplain of the Amu Darya lies the Central Asian riparian woodlands. These woodlands, locally known as tugai, represent critical habitat for many migratory wildlife. Vegetation in this area is comprised of poplars (Populus diversifolia, P. pruinosa), dzhidda (Elaeagnus oxycarpa), willows (Salix spp.), and tamarix (Tamarix spp.). The herbaceous vegetation includes steppe, desert, and swamp species.

Description of endemic fishes

There are no endemic species in the Aral Sea.

Other noteworthy fishes

The Aral Sea basin once supported a large number of forms/subspecies endemic to the basin (including the Syr and Amu drainages). These are Luciobarbus capito conocephalus, Luciobarbus brachycephalus brachycephalus, Alburnus chalcoides aralensis, Aspius aspius iblioides, Rutilus rutilus aralensis, and Salmo trutta aralensis. Some of these forms survived in a few riverine sections of Syr and/or Amu, or developed populations in recently constructed reservoirs.

The Aral migratory trout (Salmo trutta aralensis) was an exciting example of brown trout in the southeastern part of the ecoregion. However, it is most likely extinct since there have been no records for the last 50 years.

The Aral population of Acipenser nudiventris, the famous Fringebarbel sturgeon, was once abundant in the Aral Sea basin, migrating up the Syr and Amu rivers up to 2600 km for spawning. It almost disappeared by the end of 1960s, and there have been no records in Kazakhstan for the last 25-30 years. It was later stocked and introduced in some upper sections of the Syr, Amu, and Chu rivers, but is still rare.

The Aral barbel (Barbus brachycephalus brachycephalus) had once been the second (after the Fringebarbel sturgeon) most valuable commercial fish of the Aral Sea. It attained the length of 1 m and weighed over 20 kg. It was a migratory fish that travelled far upstream for wintering and spawning. The mass migration took place in July and coincided with the maximal water level in the Syr and Amu rivers. Dam construction, and later salinization, contributed to its decline. However, it survived in the middle and upper sections of the Amu Darya and Zeravshan rivers.

Ecological phenomena

The Aral Sea was historically a unique example of a large, closed lake with brackish water. It was populated by primary freshwater fauna adapted to brackish water conditions, but able to spawn in freshwater.

Justification for delineation

The ecoregion is delimited according to the former borders of the Aral Sea basin. However, the Syr Darya delta and connected lakes, as well as the Small Aral Sea, belong to the Lower and Middle Syr Darya ecoregion [629] because of the recent transformations of the Aral Sea hydrographical and hydrobiological characteristics. Historically, the Aral Sea basin is defined as a unique large, closed, and brackish lake that originated as a depression filled with river waters. It supported a poor, but unique assemblage of migratory and semi-migratory fishes adapted to forage and winter in the "marine" conditions of the lake.

Level of taxonomic exploration

Good