Boundaries

The ecoregion includes the headwaters of the Irtysh [Ertix He = Qara Ertis] River downstream to Ust’-Kamennogorsk (China, Khazakstan), including Lake Zaysan [Zhaysang Koli] (now, partly, the Bukhtarminskoye Reservoir).

In the southwest the ecoregion is bordered by the Tarbagatai Ula [Tarbagatay Nuruu = Tarvagatayn Nuruu] Range, which divides the rivers of the Lake Zaysan Depression and Lake Alakol tributaries, including Emel’ and Urdzhar, among others (in ecoregion 624). In the west, the ecoregion is contiguous with the Ob’ ecoregion [602] along the slopes of the Kalbinskiy and Ul’binskiy ranges. The border crosses the Irtysh River at Ust’ Kamennogorsk and runs eastward along the Ivanovskiy Range to include the Ul’ba River drainage. In the northeast, the Holsun and Listvyaga ranges divide the Katun’ headwaters (in ecoregion 604) and the Bukhtarma [Buqtyrma] River drainage.

East of Tarbagatai Ula, the Saur Range [Sauyr Zhotasy = Sai-li Shan] and sandy deserts of Northern Dzhungaria (south of the Urungu [Ulungur He] River) form the southern border of the ecoregion, whereas the Baytik Mountains [Baitag Bogd Uul] and Bauur-Huuray Depression form its easternmost extremity. Further to the north and northwest, the Mongolian Altai [Mongol Altayn Nuruu] Range divides the drainages of the Bulgan-Gol and Chigil rivers (Urungu River intermittent tributaries) and the Western Mongolia ecoregion [622].

The Chinese part of the Ertix He drainage lies within the Sinkiang-Uyghur Autonomous Region in China (Xinjiang Uygur Zizhiqu in Mandarin). It is also referred to as Eastern Turkestan or Chinese Turkestan.

Topography

The Irtysh River rises from the glaciers on the southwestern slopes of the Altai Mountains in Sinkiang, China. Up to its influx into Lake Zaysan it is called the Chernyi Irtysh. In that area it receives tributaries – Ulkum-Ulasty, Kenderlyk, and Kaldzhir – rising from Lake Markakul and other rivers.

Lake Zaysan lies in a depression bordered by the Altai, Kuruchum, and Narym mountains in the north and the Tarbagatai, Mokran, and Saur mountains in the south. The lake is situated at an altitude of 386 m above sea level. It stretches 110 km from the southeast to northwest. Its maximum width is 30 km, maximum depth is 8 m, and area is 1788 km². Lake Zaysan empties into the Irtysh River. Until the Ust’-Kamenogorsk the Irtysh River flows between the spurs of the Altai Mountains. In that area the Irtysh River has a mountain character, with a full flow from mountain tributaries like the Kurchum, Bukhtarma, Ulba, Uba, and Shulba rivers.

Lake Markakul is located in the lowest part of the graben delimited by the Kurchumskiy Range in the west and north, Azutau Range in the south, and Sorvenskovskiy Belok Range in the east. It is a large lake in the Altai region, with an area of 465 km², length 38.4 km, width 19.4 km, and the maximum depth of 27 m in the middle of the lake. The bottom relief is smooth. The lake has around 50 affluents, but only one river flows from it and connects the lake with the Upper Irtysh. Just downstream from the river’s lake source, large waterfalls act as a boundary for the lake fauna.

Freshwater habitats

In the upper reaches tributaries abound in waterfalls and flow in narrow ravines. In the lower reaches up to the estuaries the river channel has many branches, low flooded islands, and shoals. The rivers are fed by snow and rain; underground water sources are insignificant. Water levels begin to rise in late April – early May, with several floods occurring before ice cover is established. The maximum water level is observed in June. Sometimes maximum levels shift toward the end of May; these are called melt waters.

Lake Markakul freezes at the end of November and the ice melts by the second half of May. The water level is rather stable, and changes do not exceed 0.5 m. The highest level occurs in June-July, and the lowest level occurs in October-March.

Terrestrial habitats

A large part of the basin is mountainous, with a distinct vertical zonality. Lake Markakul is located at 1434-1450 m asl, whereas the framing ranges reach heights up to 2500-3305 m. The mountains are covered by forest, forest-steppe, meadow, and tundra. Most of the western and southern part of the ecoregion is semi-desert.

Description of endemic fishes

Only a couple of species (Barbatula altayensis and Gobio acutipinnatus) are endemic to the ecoregion. Barbatula altayensis is described from the Chinese part of the drainage. There is no data on this species. Morphologically, the endemic gudgeon (Gobio acutipinnatus) probably is a relict of the pre-glacial epoch. However, biological data is missing.

Other noteworthy fishes

This ecoregion once had an unusually abundant population of lenok (Brachymystax lenok).  This was greatly diminished due to overfishing, but now a nature reserve has been established in the area around the lake. This population deserves special attention since the lenok in other areas of the Upper Irtysh and Upper Ob’ rivers may be extirpated.

Inconnu (Stenodus leucichthys) from the Bukhtarma-Zaysan population is a unique resident form from the Upper Irtysh drainage. It has experienced a disastrous decline in its abundance. From 1950 to 1954 catches exceeded 30 tons per year. Now it occurs rarely, mainly in connection with fisheries on migration routes and also during its downstream migration outside Kazakhstan. To preserve the population it is necessary to organize artificial culture, and to regulate fisheries in the upper reaches of the Chernyi Irtysh.

The ecoregion contains a couple of subspecies that may be of specific status (Barbatula toni markakulensis and Triplophysa strauchii zaisanica). The loach (Barbatula toni markakulensis) probably is a relict of the pre-glacial epoch. However, biological data is missing. Zaisan stone loach (Triplophysa strauchiizaisanicus) inhabits small left-bank tributaries of the Irtysh River, mostly in the outlets of mountain springs. This subspecies is spread locally, and is rare. Our own collections indicate that there are undescribed species of so-called Triplophysa in the basin.

Zaisan minnow (Phoxinusphoxinussedelnikowi) inhabits small left-bank tributaries of the Irtysh River, mostly in mountainous parts. This subspecies is spread locally, although it is numerous within its habitats.

Justification for delineation

The ecoregion is delimited by the basin of the former Zaysan Depression. The native fish fauna is unique by having a complex composition of Siberian species, Central Asian species, and taxa of local origin.

Level of taxonomic exploration

The taxonomy of many taxa needs clarification. There are probably undescribed species.