Boundaries

This ecoregion includes the entire drainage area of the Shilka River, and extends down where it meets the Argun River.  Both the southern and southeastern borders of the ecoregion follow the divide (Dutugtu Uul Range in the west, and the Nercenskiy Khrebet and the Borshchovochnyy Khrebet ranges in the east) between the Shilka and Kerulen [also known as Herlen Gol or Herlen He] rivers, as well as the left-hand tributaries of the Argun\' River [618].

In the northeast, the ecoregion is contiguous with the Middle Amur drainage [617] along the southeastern slopes of the Amazarskiy Khrebet Range. Further westwards, the ecoregion’s border moves along the Khorkovyy and Tungirskiy Ranges, and the southern slopes of the Olekminskiy Stanovik Mountains between the Olekma River [608] and left-hand tributaries of the Shilka River.  The border also separates the Kirenga River [608] and the Nercha River.

In the west, the ecoregion (namely the Ingoda drainage area) is contiguous with the Yenisei ecoregion.  The Khilok River, a tributary of the Selenga River [605], are the closest water bodies along the Yablonovyy Khrebet Range.

Topography

The Shilka River runs for 560 km in a semi-mountainous region.  The river is formed by the confluence of the Ingoda and Onon rivers, and its catchment area is 206000 km². The Ingoda River is a typical mountain river, roughly 690 km long, 1.5 m deep, and flowing at a rate of 1.5 m/c.  The river’s very upper reaches pass through a narrow gorge.  The Onon River is a 1032 km long steppe river, and also contains several rifts and riffles.

Freshwater habitats

Along its entire course, the Shilka River and its tributaries have a pronounced current—roughly 0.4 to 3.0 m/c.  The river is mainly fed by summer rainfall, and floods after winter snow-melt.  Extreme flooding also occurs during periods of heavy rain from July until August.  The water begins to freeze over at the end of October, and melts again in early May.

Terrestrial habitats

Most of the catchment is located on highlands on wide divide plateaus. The river flows between steep, forest-covered banks. Dominant terrestrial ecoregions include Daurian forest steppe, Trans-Baikal conifer forests, and East Siberian taiga with pockets of Trans-Baikal Bald Mountain tundra.

 

Description of endemic fishes

Bagrid catfish (Pseudobagrus herzensteini) is a species reliably known in only two areas—the Onon and Shilka rivers. A taxonomic study is needed to confirm the range. The species is believed to be restricted to hilly streams.

Other noteworthy fishes

Very little is known about Soldatov\'s gudgeon (Gobio soldatovi tungussicus), a species initially described in the Lena River drainage, before being reported in upper reaches of other Lena River tributaries. There have been no collected specimens. If the species’ distribution and status were confirmed, it would serve as an example (along with Hucho taimen, Phoxinus czekanowskii and P. lagowskii) of the historical connection between the Lena and Amur drainages.

Ecological phenomena

There are no peculiar phenomena.

Justification for delineation

The Upper Amur catchment [618 and 619] has very different geoclimatic conditions from the other parts of the Amur basin. The catchment occupies the most elevated part of the basin (350-2500 m asl). It’s characterized by less humidity, severe continental climate, and a taiga-steppe landscape. The Bolshoy Khingan Range (also known as Da Hinggan Ling) stops monsoons, and represents the orographic border of the upper basin. At the same time, the northern Shilka basin is clearly different from the southern regions, evident in contrasting fish fauna. In general, the ecoregion is characterized by the predominance of rheophylic species, and has only one endemic species.

Level of taxonomic exploration

Fair