Boundaries

The Tarim Depression is a large endhorheic basin that lies between the southern slopes of Tan-Shan (Khalyktau [Halik Shan] Ridge and the Kokte-ketau and Boro-Khotan [Borohoro Shan] Mountains, further east), the northern slopes of the Tibet Upland region [Plateau of Tibet = Qing Zang Gaoyuan], northeastern slopes of the Karakorum [Karakorum Shan], and the Altyntag [Alton Tag= Altin Tagh = Altun Shan] Ridge in the east. The Taklamakan Desert [Taklimakan Shamo] is in the center of the ecoregion.

Topography

The Tarim Depression lies 780-800 m above sea level between mountainous ridges, and has an area of roughly 390,000 km².  A large number of rivers flow from the mountains that frame this depression. During periods of glaciation and colder climates full-flowing rivers crossed the whole hollow (which is now covered by the Taklamakan Desert [Taklimakan Shamo]), and reached the Tarim River that flowed along the northern margin. The terminal water body of the entire drainage system was Lake Lob Nor [Lop Nur], which changed location several times according to geological data. At present, most of the rivers do not connect with each other in their lower reaches since water is diverted for irrigation.

Freshwater habitats

Streams of the Tarim Depression flow from high mountains, and have a typical mountainous character in their upper reaches. Entering the plain, they become slow and much wider, forming branches and oxbows. Because of the general aridization of the climate and human impact, the water content has been heavily reduced. In the 20^th century the area of Lob Nor decreased from 28,000 to 2500 km², and in 1950 it dried up completely. According to data from literature, water from Tarim stopped reaching the lake in 1942 when both the Tarim and Konche-Dar’i [Konqi He] rivers changed their courses due to unknown reasons, and turned to the east at the town of Takanlik. Their water is now lost in sands.

Terrestrial habitats

Most of the ecoregion is covered by the Taklimakan Desert terrestrial ecoregion. Higher elevation ecoregions that circumvent the desert include Tian Shan montane steppe and meadows in the north, Pamir alpine desert and tundra in the west, North Tibetan Plateau - Kunlun Mountains alpine desert in the south, and Quilian Mountains subalpine meadows and Alashan Plateau semi-desert in the east. Pockets of riparian forests occur along the Tarim River. 

Description of endemic fishes

The only endemic species in the ecoregion is Phoxinus grumi. This is a “good" species demonstrating clear links with Phoxinus species of the Balkhash and Issyk-kul lake basins. Its distribution shows a remarkable example of occurrence on the margin of the generic range. Its exact distribution has not been studied. It may easily be extinct because of the dessication of small water bodies it inhabits.

Aspiorhynchus (a "good” genus from a taxonomic point of view), is a near-endemic monotypic genus (with ecoregion 707). It inhabits larger rivers and lakes within the Tarim drainage.  The species had been quite abundant before the 1980s in one of the large lakes, Bosten. Being a large (up to 770 mm and 3 kg) predator it served as the main commercial fish in the lake. In recent decades its numbers have drastically declined. Now the species is close to extinction because of overfishing and sharp competition with non-indigenous fishes. The European perch (Perca fluviatilis), predating on schizothoracine species and loaches that are the main food object of Aspiorhynchus, markedly destroyed its forage reserve. Besides this, Aspiorhynchus feeds on mollusks, which are now consumed by the introduced Mylopharyngodon. The construction of irrigation dams cut off the spawning migratory routes of the species.

Another near-endemic species, Schizothorax biddulphi, before the 1960s had been the main object of fisheries, together with Aspiorhynchus laticeps. The construction of dams and the introduction and stocking of European perch (Perca fluviatilis), grass carp (Ctenopharyngodon idella), and black carp (Mylopharyngodon piceus) considerably undermined its abundance. Exact data are not known.

Justification for delineation

This ecoregion is a closed endorheic drainage that is now separated into several close streams.

Level of taxonomic exploration

Poor. Urgently needs revision.