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# of Endemic Species
Major Habitat Type:
This ecoregion encompasses the drainages of Arctic rivers from the Indigirka River eastward to Chaunskaya Guba Bay. In the west, the Indigirka River drainage is separated from the Khroma and Yana rivers (ecoregion 608) by the spurs of the Polousnyy Kryazh Range and the Cherskogo Range. The Suntar-Khayata Range divides the Indigirka drainage from the Aldan (Lena tributary, ecoregion 608) and rivers of the Okhotsk Coast  ecoregion in the south. In the west, the Kolymskiy Range forms the divide between the Kolyma-Omolon drainage and coastal rivers of the Zaliv Shelikhova Bay (614) and the western Koryakia (Penzhina River, 612). The eastern spurs of the Oloyskiy and Anyu’skiy ranges form the border of the ecoregion with the Anadyr’ River drainage (ecoregion 610). Further northeast, the border runs along the northern slopes of the Anadyrskoye Ploskogor’ie Upland and, crossing the Chukotskiy [Anadyrskiy] Khrebet Range, along the southern slopes of the Ekvyvatapskiy Range and western slopes of the Khrebet Chankal’skogo Range.
Drainages flowing into:
East Siberian Sea (Arctic Ocean)
Main rivers or other water bodies:
The ecoregion’s main water bodies include the Indigirka River, Alazeya River, Bol’shaya Chukoch’ya River, Kolyma River, Omolon River, Bol’shoy Anyuy River, Malyy Anyuy River, Chukoch’e Lake, Nerpich’e Lake, Rauchua River, Chaun River, and Pegtymel River.
The Indigirka River, formed by the confluence of the Khastakh and Taryn-Yuryakh rivers, empties into the East Siberian Sea downstream from the village of Allaikha. The length of the river is 1790 km, and drainage area is 360 000 km2. The Indigirka is split into two characteristic parts: 1) from the confluence of the Khastakh and Taryn-Yuryakh rivers to the village of Maior-Krest; and 2) from tMaior-Krest downstream to the estuary. Up to Maior-Krest the river flows in mountainous conditions; here, its valley represents alternating lake-like extensions (up to 20-40 km) and narrowed parts (up to 1-0.5 km) where the river flows between high and rocky coasts. The average slope is 0.8-1.1‰. Flow velocities fluctuate from 2.0 to 3.5 m s-1. Rifts are most numerous in the section (89 km in length) between the estuaries of the Talyn’ya and Tikhon rivers. Here, the river cuts through the northern chain of the Ulakhan-Chistai Ridge and flows in a deep ravine, occupying nearly its entire bottom. The flow velocities of the turbulent stream exceed 4 m s-1. In the second section (730 km in length) the river flows in a wide channel through an extensive plain. The delta begins 130 km from the estuary where the Russian Ust’inskaya anabranch separates left from the river channel. The delta’s area is 5500 km2.
The Kolyma is the largest river of northeastern Siberia. It length is 2600 km and catchment area is 644 000 km2. The river originates on the slopes of the southern spurs of the Chersky Ridge. Throughout part of its upper reaches it is directed southeast, whereas the rest of its length is directed north-northeast. For more than 1000 km the river flows in mountain conditions. Its relatively wide river channel is undulating and is split into numerous branches and anabranches. In some areas the valley narrows and is reminiscent of a deep canyon. In the lower reaches the Kolyma River flows into the wide Kolyma Lowland that is covered by numerous lakes. It forms a wide delta where is empties into the East Siberian Sea.
The Kolyma Lowland and the Alazeiskaya Lowland are characterized by an exceptional abundance of lakes.
The topography of the northern part of the ecoregion is flat and rolling tundra, becoming more mountainous toward the south in the Verkhoyano-Kolyma Mountains, where elevations reach over 2800 m.
Winter is prolonged and severe and summers are short but warm, reaching -13 ºC in July. Part of the ecoregion is located within the Arctic Circle and is covered in frozen ground and permafrost.
The upper reaches of rivers in this ecoregion have a mountain character; in the middle reaches, a transitional character; and in the lower reaches the rivers usually spread out onto a plain where they acquire features of typical plain rivers. The headwaters of the Yana, Indigirka, and Kolyma rivers are located in the Verkhoyano-Kolyma Mountains, and their estuaries are found in the Arctic Lowland.
Rivers of this ecoregion are generally characterized by a high spring flood, followed directly by a number of summer floods resulting from rains. Eventually the flow slows to a point where it may stop completely.
The average annual water discharge of the Indigirka is equal to 1800 m3 s-1. In winter the river is shallow and in the lower reaches freezes to the bottom. The amplitude of water level fluctuation reaches 8-10 m. The river freezes in early October and opens up in early June. In winter, large frazil ice forms in rivers of the Indigirka drainage, frequently filling the entire bottom of the valley.
The average annual water discharge of the Kolyma is equal to 3800 m3 s-1. The amplitude of the water level fluctuation reaches 13 m in the lower reaches. During spring ice jams occur, and the water level reaches 16 m above the mean water level. The Kolyma does not freeze to the bottom. Rivers of the Chaun estuary are short, and in some winters they freeze to the bottom.
The ecoregion is comprised of Cherskii-Kolyma mountain tundra, Northeast Siberian taiga, and Northeast Siberian coastal tundra. The Northeast Siberian taiga is dominated by larch (Larix cajanderi) and Betula pendula. Populus suaveolens and Chosenia macrolepis occur in river valleys. The Northeast Siberian coastal tundra is dominated by dwarf shrubs and tundra species such as cotton grass (Eriophorum sp.), sedges (Carex sp.), dryas (Dryas punctata), willows (Salix sp.), crowberry (Empetrum sp.), cranberry (Vaccinium vitis-idea), and mosses (WWF 2001).
The fish fauna of the ecoregion is homogeneous. Differences among rivers are only limited to the absence of some rheophilous fishes in the Alazeya and Chukoch’ya rivers and a decline in the number of species in small rivers in the western part of the ecoregion. There are nearly 40 species, which include a handful of typical freshwater species and one endemic species, Cherskii’s char (Salvelinus czerskii). Fishes of the Salmonidae family are dominant. Siberian cyprinids are also relatively abundant (three genera and five species). The ecoregion’s ichthyofana generally appears to be Siberian, but the number of species is notably smaller than in Siberian rivers – Lena, Yenisei, and Ob – further west. The following species are absent from this ecoregion: starlet (Acipenser ruthenus), Dryanin’s char (Salvelinus drjagini), Yakutian char (S. jacuticus), taimen (Hucho taimen), tugun (Coregonus tugun), arctic grayling (Thymallus arcticus), roach (Rutilus rutilus), ide (Leuciscus idus), Amur minnow (Phoxinus lagowskii), Tinca tinca, Siberian gudgeon (Gobio cynocephalus), Soldatov’s gudgeon (G. soldatovi), and Siberian sculpin (Cottus sibiricus). In all the three large Siberian rivers – Lena, Yenisei, and Ob – the endemic S. czerskii is absent.
Fauna within rivers of the Chaun estuary and Pegtymel and Rauchua rivers is depauperate and lacks most true freshwater forms, such as longnose sucker (Catostomus catostomus catostomus), northern pike (Esox lucius), European perch (Perca fluviatilis), Crucian carp (Carassius carassius), and lake minnow (Phoxinus percnurus). There are only two primary freshwater species, as well as numerous migratory salmonids. Historically, this fauna belonged to the Kolyma ichthyofauna, which is supported by fossil remains of Kolyma species from Late Pleistocene deposits of the Chaun.
Description of endemic fishes:
Cherskii’s char (Salvelinus czerskii) is a lake char, and is currently considered endemic to the ecoregion. Its status needs further clarification (in general, it belongs to the Salvelinus alpinus complex). There is also contradictory data suggesting that it may also occur in lakes of the Yana River drainage and the lower Lena River. If this is true, the species may in fact be near-endemic to the ecoregion.
Other noteworthy fishes:
Salvelinus alpinus orientalis is a lake char described from the lakes of the Indigirka River. Its status and range need clarification.
Longnose sucker (Catostomus catostomus catostomus) is a benthic dweller that inhabits rivers and lakes of the ecoregion. It migrates for spawning into smaller tributaries where it lays eggs on gravel or sandy bottoms. It is abundant.
In the Indigirka and Kolyma rivers, fishes migrate from the main river beds to lowland lakes through channels to forage. They migrate back for spawning and wintering.
An analysis of the composition of this ecoregion’s fish fauna is important in understanding historical fish dispersals and the affinities among fish faunas of Siberia and North America. The gradual impoverishment of Siberian ichthyofauna east of the Ob River can testify indirectly to the predominant direction of dispersal of the ichthyofauna from west to east. This is further supported by some Siberian species that penetrated into rivers of the Pacific Ocean basin and even into North America. Such latitudinal dispersals could have successfully occurred only in the periods of powerful regressions of the seas at the end of the Tertiary through the Quaternary, when the neighboring river sisytems of Siberia and Alaska were connected through the extensive dry shelf of the Arctic Ocean. The ancient, now inundated, valleys of Siberian and Alaskan rivers have been discovered on shelves of Arctic seas. This can also explain how limnophilous species (acipenserids, coregonids, cyprinids, percids, pike), ecologically connected with the plain areas of rivers, could have dispersed. Another avenue of latitudinal dispersal was through the tectonically formed catches in the upper reaches of rivers and watersheds near glacier lakes; this way of dispersal was preferable for rheophilous fish species such as Prosopium, Thymallus, Catostomus, and Phoxinus.
Justification for delineation:
The ecoregion is defined by rivers of the Kolyma-Indigirka Lowland that have a fish fauna that is generally Siberian in character. However, the number of species in it is notably smaller than in large Siberian rivers (Lena, Yenisei, and Ob) further west due to more severe climatic conditions and, thus, limited ecological niches.
Level of taxonomic exploration:
Chereshnev, I. A. (1998). "Biogeography of freshwater fishes of the Far East in Russia" Vladivostok: Dal'nauka.
Chereshnev, I. A. (1990). "Composition of fish fauna and distribution of freshwater fishes of the North-East of Russia" Vopr. Ichthyol 30(5) 836-844.
Chereshnev, I. A. (1996). "Biological diversity of freshwater fish fauna of the North-East of Russia" Vladivostok: Dal'nauka.
Chereshnev, I. A., Shestakov, A. V., et al. (2001). "Guide to freshwater fishes of the North-East of Russia" Vladivostok: Dal’nauka.
Kirillov, A. F. (2002). "Commercial fishes of Yakutia" Moscow: Nauchnyy Mir.
World Wildlife, Fund (2001). "Terrestrial Ecoregions of the World" 2005 (2005; www.worldwildlife.org/science/ecoregions/biomes.cfm).