Boundaries

The ecoregion includes the upper Biya and Katun’ rivers in the headwaters of the Ob’ River. This includes the Katun’ River headwaters down to its confluence with the Chuya River, as well as the whole Chuya drainage area. The ecoregion also includes the Chulyshman River, a headwater of the Biya upstream from Lake Teletskoye. In the west, southwest, and south, the border follows: 1) the Konsuyskiy Range, which divides the Koksa River headwaters and Uba River headwaters (in the Ob’ ecoregion [602]); 2) Holsun and Listvyaga ranges, dividing the Katun’ headwaters and the Bukhtarma [Buqtyrma] River drainage and; 3) the southern edge of the Ukok Plateau and the Saylyugem Range [Siylugemiyn Nuruu], which divides the Upper Chuya and rivers of Western Mongolia [622]. The eastern border of the ecoregion follows the Chrebet Chikhachova Range, and curves to separate Lake Kyndyktykul [Khindiktig-Khol] and Lake Dzhulu-Kul (part of the Upper Chulyshman River). The Shapshal’skiy Range divides the Chulyshman drainage and Yenisei headwaters (Kemchik River).

In the east and southeast the ecoregion’s border runs along the Terektinskiy Range down to the confluence of the Chuya and Katun’ rivers (below this point, the Katun’ basin belongs to Ob’ [602]). Further east along the Saldzhar Range and then north along the Sumul’tinskiy Range the border reaches the southernmost extremity of Lake Teletskoye [602]. The border then extends northward along the Abakan Range, which forms the border with the Yenisei ecoregion [605], and along the eastern margin of the Zapadno-Sibirskaya Nizmennost’ Plain (following the western margin of the Yenisei drainage).

Topography

The ecoregion is a major part of the Altai – a plateau-like mountain range that is deeply dissected by river valleys. This plateau in some areas has the appearance of hilly plains and open steppes separated from valleys with high ridges.

Only the highest and the most dissected ridges of the Altai Mountains have the appearances of alpine mountain ridges with dentate ridges and acute shapes. One of the largest ridges is Tabyn-Bogdo-Ola (five sacred mountains). Its highest point is recorded at 4653 m abs. The Chuiiskii and Katunskii ridges are also high, with elevations around 3000 - 4000 m. The highest point of the Katunskii Ridge, and at the same time of the entire Altai, is Belukha Mountain, rising 4620 m above sea level. The Altai is a center of recent glaciations, with a total area of 596 km² and 754 glaciers. The snow line occurs at an altitude of 2300—3200 m. The largest number (60%) of glaciers are concentrated at the tops of the Katunskii Ridge, with Belukha Mountain the center of glaciation in the Altai. The Northern Chuiskii Ridge and the Southern Chuiiskii Ridge are also glaciated.

The ecoregion is characterized by a dense river network that includes streams of two river systems that are not connected within the ecoregion.

Katun’, the left-hand upper constituent of the Ob’, rises on the southern slope of Belukha Mountain, and bends around it, nearly forming a circle. From the estuary of the Argut, the Katun’ turns abruptly and flows north. Nearly 665 km from its source it is confluent with the Biya River, not far from Biisk. Its catchment area is 60,900 km². The river has a mountain character; its valley is deeply cut and its channel abounds in rapids and small cascades. Katun’ is characterized by a notable amount of water. Its mean annual water flow is equal to 630 m³ sec^-1, whereas the module of flow is 10.3 l sec^-1 km^-2. The drainage of the Katun’ includes extensive highland steppe areas characterized by a relatively small surface flow. The main tributaries of the Katun’ are the Chuya and Argut rivers.

The Chulyshman River rises in Lake Dzhulu-Kol’ at approximately 2176 m above sea level, and falls into the southern part of Lake Teletskoye. The length of the river is 203 m. After flowing out of Lake Dzhukulu-Kol’ the river has a small slope, and in some areas splits into separate branches. After this its slope increases and the river flows at a high rate over underwater blocks of granite. The largest tributaries of the Chulyshman are the rivers Bashkaus (left tributaries), Shavla, and Chulcha (right tributaries).

Due to the predominant latitudinal direction of the ridges, rivers in this ecoregion have transversal valleys of considerable length. For instance, the Argut River cuts between the Katun’skii and Chuiiskii ridges in the ravine with a depth of up to 2000 m.

Depending on the position of the drainage in the mountain system, longitudinal profiles of rivers have a concave or convex configuration. The former is characteristic of rivers flowing down ridges with sharply outlined shapes reminiscent of alpine ones; these rivers include Katun’. The latter profile is typical of rivers flowing down plateau-like highlands; this includes the rivers Chuya, Chulyshman, and others. In their upper reaches these rivers flow on a plain elevated high above sea level, and have low slopes and swampy banks. In the middle reaches they cut deeply into the plateau, their slopes increase, and their currents assume a mountain character. In the lower reaches the slopes of these rivers decrease again and their flow becomes calmer.

Freshwater habitats

High precipitation and mountainous relief provide favorable conditions for surface flow. As a result, rivers in this ecoregion possess high water volume. Rivers of the western Altai have particularly high water volume due moisture-laden winds blowing from the west. The relative amount of water in the rivers here reaches 15—25 l/sec km^-2, and in some areas (the upper reaches of the Katun’), up to 56 l/seckm^-2. Rivers in the central Altai (Chulyshmanskoye and Ukok plateaus) are characterized by relatively low water volumes.

The majority of rivers of the Altai are characterized by the following: 1) a relatively high spring flood, protracted up to the first half of the summer because of melt waters from different altitudinal zones at different periods; in addition to the main spring flood are floods caused by rains; 2) weakly pronounced summer mean water, frequently interrupted by floods caused by rains; these have lower water levels than spring floods; 3) the lowest amount of water occurs in the winter period.

In the foothill zone, river drainages that do not exceed 800 m above sea level experience one relatively high spring flood, and mean water that is distinctly pronounced. In the alpine zone, river basins above 2000 m experience a spring-summer flood from snowmelt and glaciers. Here, summer mean water is not pronounced.

The ice regime of Altai rivers is complex. The development of ice phenomena is influenced by slopes and flow velocities of rivers. The combination of climatic conditions with the character of river currents in separate areas provides for drastic differences in ice phenomena. The majority of rivers of the Altai, except for rift areas, are frozen in the second half of November. The most significant rifts are not frozen throughout the entire winter. The rivers flow from the second half of March through the end of April. This is sometimes accompanied by ice jams that are caused by an earlier opening in the upper reaches, where relatively high flow velocities promote the rapid destruction of the ice cover.

Terrestrial habitats

The ecoregion is comprised primarily of alpine meadow and tundra, alpine forest, steppe, and conifer forests.

Description of endemic fishes

The ecoregion contains no endemic species.

Other noteworthy fishes

Altai osmans, Oreoleuciscus species, are widespread in landlocked water bodies of the Central Asian Internal Basin of Mongolia at altitudes from 1000 to 2238 m above sea level. Outside this area they are present only in the upper catchment of the Ob’ River. The swampy nature of highland streams, which in some places may still connect (or in the past connected) the two catchments, could possibly have assisted fishes in crossing the divide. Osmans are lake fishes, but they also inhabit rivers with slow currents, avoiding the fast current of mountain rivers. In most water bodies of the ecoregion osmans are often the only fish inhabitants. They feed on a variety of objects depending on the size of the fish.

Ecological phenomena

Predatory fishes are completely absent in the ecoregion, apart from preying adult individuals of Altai osman. High flow velocity, rifts, and even cascades separate the upper reaches from the lower parts of the rivers, making them impassable for migrants from the lower reaches. Thus, all migrating anadramous forms are completely absent in this ecoregion.

Justification for delineation

The separation of the transitional Chulyshmano-Chuiiskii area within the zoogeographic Western Siberian District adjoining the Western Mongolian District from the northwest is well corroborated (Gundrizer 1964). The total area is approximately 30,000 km². The area includes extensive alpine steppes (Kuraiskaya, Chuiiskaya), plateaus (southern part of the Chulyzhmanskoye Plateau, Ukok Plateau, and others), rapidly flowing rivers, and numerous lakes that are extremely poor in fishes and are characterized by peculiar species compositions. This area includes drainages of the upper and middle reaches of such relatively large rivers as Chulyshman, Bashkaus, Chuya, and Argut.

Level of taxonomic exploration

Poor