Boundaries

The ecoregion includes the drainage of the Syr Darya [Sirdaryo] River, which lies to the north and west of the Central Asian Highlands (Talas River exclusive). In the extreme northwest the ecoregion extends in a fingerlike projection to encompass the lower Syr Darya, its delta, and the Malyy Aral [Small Aral] Sea (see Aral Sea Drainages [629]). The western border (with the Middle Amu Darya [630]) runs southward along the eastern slopes of the Bukantau Mountains, and then crosses the Peski Kyzylkumy [Qizilqum] Desert and Golodnaya Step’ [Betpaqdala] Desert. It then extends down to the northern slopes of the Turkestanskiy Range, which are west of the Fergana Valley [Fergana Oroonu = Fergana Oydungu = Vodii Farghona]. The border then runs north along the the northwestern spurs of the Kuraminskiy, Chatkal’skiy [Chotqol], and Pskemskiy ranges, as well as the main range of the Karatau Mountains (cutting off the upper reaches of the Angren [Angrensay], Chirchik [Chichiq] and Arys tributaries, which belong to the Upper Amu Darya ecoregion [631]). The Karatau Range [Qaratau Zhotasy] is the divide between the righthand Syr Darya tributaries and the Talas River drainage. From the northern slopes of the Karatau Range the border of the ecoregion travels east across the Peski Muyunkumy [Moinkum = Moyynqum] Desert, and further eastward along the northern slopes of the Kirgizskiy Range [Qyrghyz Zhotasy] to the easternmost margin of the Chuyskaya Dolina Valley (east from the town of Tokmak) (the border with 627). From this point, the border of the ecoreion runs northwest along the Zhotyzhol and Zhentyktas ranges and Chu-Iliyskiy Gory Mountains, which are the divide between Lake Balkhash [Balqash Koi] basin (Balkash-Alakul [624]) and the Chu [Chuy = Shu] River drainage. The border with the Balkash-Alakul ecoregion [624] then runs north across the Zhel’tau and Aytau mountains to the western slopes of the the Kazakhskiy Melkosopochnik Upland [Qazaqtyng Usaqshoqylyghy]. Here it divides the upper headwaters of the northern tributaries (former tributaries) of Lake Balkhash (Balkash-Alakul ecoregion 624), Sarysu River drainage (ecoregion 626), and the Nura River system (Ob ecoregion [601]). In the north, the ecoregion includes the whole drainage of the Sarysu River, separating it from the tributaries of Lake Tenghiz in the Nura River drainage.

Freshwater habitats

The waters of the Syr Darya are characterized by high turbidity (approximately 2000 g/m³), although it is lower than in the Amu Darya. The total amount of alluvium carried by the river to the outfall is 12 million tons per year, whereas the Amu Darya carries up to 100 million tons per year. The river also has a third less water volume than the Amu Darya. Like the Amu Darya, the Syr Darya loses part of its water flow (approximately 170 m³/sec) crossing the desert.

From the Ferghana Valley the Syr Darya flows along a wide valley that is swampy in some areas and contains numerous bayous. In the lower reaches the river channel is elevated above the adjoining terrain. During periods of high water extensive areas are flooded, particularly during the summer flood and during ice jams. In March and April, snowmelt from the plain and foothills results in spring floods on the Syr Darya. The uneven melting of glaciers and alpine snows causes several separate short floods to occur in different parts of the drainage. In May the second main flood begins, reaching its maximum in July. Minimum flow is observed in December and January. At present the natural regime of the river is highly modified, with a large portion of the water from the mountains diverted for irrigation. As a result natural flooding may be absent.

In 1989 continued desiccation of the Aral Sea led to its division into two lakes, which have evolved separately. The Small Aral Sea, located in the north, receives run off from the Syr Darya River. This inflow, along with precipitation on the sea’s surface and groundwater inflow, has created a positive water balance to allow some flow from the Small Sea to the Large Sea via a connecting channel across the former Berg’s Strait.

The salinity of the Aral Sea was about 28-30 g/l when it divided into two lakes at about 40 m asl. Seven fish species inhabited the Aral at the time of division. From aboriginal species only the southern ninespine stickleback (Pungitius platygaster aralensis) remained. The dam constructed in the Berg’s Strait raised the Small Aral Sea level to 42.8 m by April 1999, and led to a drop in salinity from 29.2 g/l (at division) to 18.2 g/l. Now, native freshwater fishes have started to enter the Small Aral from the Syrdaria Delta up to Butakov Bay. They use the sea only as a feeding ground, and spawn in the delta zone. The conditions of the delta zone are improving.

Terrestrial habitats

The terrestrial habitats of the ecoregion are dominated by semi-desert, desert, and steppe, with stretches of riparian woodlands. In the estuary areas of the Syr Darya during long inundations and high levels of subsoil waters, swamps are formed that are covered by reeds.

Description of endemic fishes

The only strict endemic is Lagowskiella dementjevi, which is a local endemic species only known from a few localities on the Chu River. It is a poorly known fish.

Other noteworthy fishes

Sharpray (Capoetobrama kuschakewitschi) is near-endemic to the Aral basin. It is distributed in the Syr Darya and Amu Darya rivers. Today it is rarely seen. The Chu sharpray (C. kuschakewitschi orientalis) in the Chu River is an endemic subspecies, and is a very rare fish if it is still extant. It hasn’t been recorded in Kazakhstan for more than 40 years.

Striped bystryanka (Alburnoides taeniatus) is also near-endemic to the Aral basin. The endemic subspecies, A. taeniatus drjagini, is only known from the Lower Chu.The subspecies is rare small-sized pelagic cyprinid. It avoids ponds and reservoirs, preferring flowing waters.

Two sturgeon species used to inhabit the basin – fringebarbel sturgeon (Acipenser nudiventris) and Syr Darya sturgeon (Pseudoscaphirhynchus fedtschenkoi). Both species are now extremely rare and have most likely fallen out of the Syr Darya basin ichtyofauna; there haven’t been any records about them for 50 – 30 years. Syr Darya sturgeon is a narrow habitat endemic of the Syr Darya River. According to local fishermen, the fringebarbel sturgeon (A. nudiventris) is rarely caught in the Syr Darya delta region, but there is no data on Syr Darya sturgeon.

Two barbel species are represented by subspecies endemic to the Aral basin – Aral barbel and Turkestan barbel. Aral barbel (Luciobarbus brachycephalus brachycephalus) is a valuable fishery species that used to inhabit the sea and lower reaches of the Amu Darya and Syr Darya rivers. At present the number has been drastically reduced and it is endangered. The Turkestan barbel (L. capito conocephalus) used to inhabit the entire Syr Darya River and Chu River. At the present the number has been drastically reduced. Both species have been sighted in the lower Syr Darya River over the last few years.

Tashkent riffle bleak (Alburnoides oblongus), Syr-Darya dace (Petroleuciscus squaliusculus), and Kuschakewitsch loach (Nemacheilus kuschakewitschi) are endemic to the Syr Darya River, and near-endemic to the ecoregion. They are mostly distributed in the middle reaches of the river up to Fergana Valley. These species occur sporadically, but they are numerous in their habitat. However, there are no reliable data in collections. They are all relatively small-sized fishes.

Ecological phenomena

Fishes of the Syr Darya drainage, particularly in its middle and lower reaches, have adapted to life in a stable flow of highly turbid water. Pseudoscaphirhynchus fedtschenkoi, with all its morphological and ecological features, demonstrates good adaptation to life in turbid flows. However, after the construction of river channel reservoirs water in the Syr Darya became much more transparent, negatively affecting this species. It is now listed as Critically Endangered, and may likely be extinct.

Justification for delineation

The drainage of the Syr Darya was subdivided into two ecoregions because the fauna of the upper reaches, with their pronounced mountain character, is different from fauna of lowland sections of Syr Darya, Chu, and Sarysu rivers. This ecoregion supports a complex fauna originated from Ponto-Caspian, Siberian, and mountainous Asian sources. The closest fauna is that of the Middle and Lower Amu Darya. however, both ecoregions have their own near-endemic species of the genus Pseudoscaphirhynchus - the most outstanding example of Central Asian endemism.

Level of taxonomic exploration

Fair