Boundaries

This ecoregion encompasses coastal rivers on both sides of the Amurskiy Liman Straight (including continental rivers and a portion of northwest Sakhalin Island, an area on the eastern coast of the Amurskiy Liman Straight, south of the Proliv Nevel’skogo Straight), the Amur River estuary, rivers of the southwestern coast of the Sea of Okhotsk northward to the Uda River drainage (inclusive), and rivers on the Shantarskiye Isles (Shantary Islands).

Note: Amurskiy Liman is not an estuary (this is not the Amur River estuary, although it is called "liman"), but just a northern part of the Tatarskiy Proliv [Tatar] Straight ("sensu lato") south of the Proliv Nevel’skogo Straight.

In the north, the ecoregion is contiguous with the Okhotsk Coast [614] and Lena [608] ecoregions along the southern slopes of the Pribrezhnyy, Stanovoy, and Mayskiy ranges. The western border of the ecoregion runs along the Khrebet Dzhagdy Range and Taykanskiy Range, which divide the Uda and Tugur headwaters and the Upper Zeya tributaries (Middle Amur [617]). In the south, the border follows the coast along the Byuko, Yam-Alin’, Kivun, and Mevachan ranges to include the smaller coastal rivers. It reaches Nikolayevsk-na-Amure, which is located at the mouth of the Amur River (the uppermost point of its estuary).

Topography

The Uda River is the largest among the rivers of the southwestern coast of the Sea of Okhotsk, adjacent to the Amur River mouth. Its length is 400 km, catchment area is 64,100 km², and average water flow in the mouth is 700 m³/ sec.

The Shantarski’y Isles [Shantary Islands] are located on the eastern side of the Sea of Okhotsk. They are a continental type of islands that were separated from the continent only 9-10 thousand years ago. The largest island, Bolshoy Shantar, is about 50 km in diameter. The largest river is Olen’ya, which flows into the Bol’shoye [Sol’enoye] Lake (16 km long). Smaller rivers and lakes are quite numerous. The islands are not mountainous, although larger ones have an elevated central part (up to 400-700 m above sea level).

The northeastern part of Sakhalin is located close to the continent, being separated from the latter by only the Nevelskogo Strait, which is shallow (7-12 m) and narrow (7.5 km in its narrowest part). This area is comprised primarily of the North-Sakhalin Plain, which in its coastal part consists of low marine terraces and a large number of small lakes.

Numerous smaller rivers that flow into the Amur River estuary also occur in the ecoregion.

Freshwater habitats

The floodplains of the Uda River, its tributaries, and other rivers are rich in marshes, which have no outflow because of the permafrost. The rivers are mostly fed from snowmelt and have a single spring flood.

Northeastern Sakhalin is characterized by a variety of lowland rivers, rivulets, channels, and lagoons, as well as many isolated swampy lakes that have intermittent interconnections with various water bodies with running water.

Terrestrial habitats

A major part of the ecoregion is located in the forest zone, whereas the coastal areas are low and marshy. The Tugur and Uda rivers have well-developed lowland plains. The northeastern coast of Sakhalin is also low and swampy. The coastal plain stretches up to 40-50 km wide at elevations less than 50 m.

Description of endemic fishes

The ecoregion contains no endemics or near-endemics.

Other noteworthy fishes

Not long ago (in 1985) a unique population of the resident rainbow trout (Oncorhynchus mykiss) was discovered on Bol’shoy Shantar Island – the only wild population in Asia outside the Kamchatka Peninsula.

This ecoregion contains some Amur River endemics (distributed in a number of Amur ecoregions) representing true freshwater fishes – redfin (Pseudaspius leptocephalus), Amur whitefish (Coregonus ussuriensis), and Amur pike (Esox reichertii).

Ecological phenomena

The fish fauna of this ecoregion contains almost the whole spectrum of ecological groups characteristic of the Amur River. These are typical rheophilic species (Brachymystax lenok), specialized limnophilic ones (Carassius gibelio), relatively eurybiont (Chanodichthys erythropterus, Leuciscus waleckii, Rhodeus sericeus), migratory and brackishwater (species of the genera Oncorhynchus, Coregonus, Pungitius, Hypomesus, Parahucho), and marine species (Cottidae and Pleuronectidae). The single exception is a group of large migratory fishes (Huso, Elopichthys, Hypophthalmichthys, Ctenopharyngodon) that need long distances for runs and downstream migrations of yearlings, and specific benthic or pelagic conditions in larger rivers for spawning and juvenile growing.

Justification for delineation

This ecoregion encompasses the Amur estuary, the Tugur and Uda rivers flowing into the Okhotsk Sea north from Amur, and a portion of northwest Sakhalin Island (an area adjacent to the Amur estuary south to the Straight of Nevelskoi).

The ecoregion delineation was supported by Taranets (1938) who first delineated the "Pre-[Amur] Liman-Sakhalin district" as possessing a depauperate Amur fauna that was clearly different from those in the north and south of the continent, as well as in the rest of Sakhalin Island. The ecoregion shares several forms with the Amur basin that are absent from the adjacent Sakhalin, Hokkaido & Sikhote-Alin Coast ecoregion [641] (in the south) and the Okhotsk ecoregion [614] (in the north): taimen (Hucho taimen), grass carp (Ctenopharyngodon idella), predatory carp (Chanodichthys erythropterus), and spotted steed (Hemibarbus maculates). It is also different from the Sakhalin, Hokkaido & Sikhote-Alin Coast ecoregion [641] by a complete absence of euryhaline and brackishwater gobies.

The ecoregion represents a former bridge between the Amur and adjacent rivers with northwestern Sakhalin during the former regression of the sea in the Late Pleistocene.

Level of taxonomic exploration

Fair