Boundaries

The ecoregion encompasses the drainages of the Chukotka Peninsula north of the Anadyr’ drainage and rivers of the Anadyrskiy Liman. The border shared with the Kolyma ecoregion [609] runs along the Pegtymel’skiy and Palyavaamskiy ranges; the border shared with the Anadry ecoregion [610] runs along the Chukotskiy [Anadyrskiy] Khrebet Range; and further south, the border runs between the Kanchalan River drainage (in ecoregion 610) and rivers of Kresta Bay and the northern coast of Anadyrskiy Bay. The ecoregion also includes Wrangel Island.

Topography

The Chukotka Peninsula is the northeastern extremity of Asia and northern region of the Russian Far East. It is part of ancient Beringia, a land bridge that joined Alaska and eastern Siberia at different times during the Pleistocene ice ages.

Rivers of the Chukotka Peninsula are notably different from other foothill rivers in the Far East. These differences are related mostly to the position of the ecoregion in the permafrost zone, and also to its geographic location. Rivers generally flow in wide valleys, and are shallow with stony or sandy bottoms.

The elevated relief of the peninsula is divided by river valleys that are located predominantly in foothills. Exceptions are the lower reaches of the Amguema River and some other large rivers that flow along the coastal plain.

Freshwater habitats

Rivers in the ecoregion are fed by snow and rain, with yearly spring floods and several rain floods. In autumn the melting layer above the permafrost stops feeding watercourses; groundwater of the meltwater alluvium beneath the riverbed is quickly depleted; and by October-December, the surface flow stops in many small and medium-size watercourses. Small watercourses (with catchment areas of 1-100 km²) may not flow for 240 days. Even large watercourses such as Amguema freeze. There is no surface flow in Amguema for four months (January -   April) despite the fact that the area of the basin is 28 100 km² and average annual run-off is 257 m³ s^-1. This is the primary difference between the freshwater habitats of the Chukotka Peninsula from that on Kamchtka, where underground feeding is predominant. For example, underground water feeds 60% of water in the Avacha and Kamchatka rivers.

Watercourses of the Chukotka Peninsula are also characterized by frequent drying, which is also accounted for by the type of feeding. Streams and even relatively large rivers can run dry during summer mean water in the absence of rains, but sometimes riverbeds of streams run dry in  autumn, before freezing. Under these conditions, the survival of freshwater fauna is only possible in the presence of drainages situated beneath riverbeds that do not freeze and do not dry. Therefore, taliks are extremely important for water bodies.

Terrestrial habitats

Terrestrial ecoregions of East Chukotka include Wrangel Island arctic desert, Chuckchi Peninsula tundra, and Bering tundra (WWF 2001).

Description of endemic fishes

The ecoregion contains three local endemic species: Dallia admirabilis, Dallia delicatissima, and Chukot char (Salvelinus andriashevi).

Dallia admirabilis is only known from the the middle and lower Amguema River drainage in the Chukotka Peninsula, where it inhabits some floodplain and thermokarst lakes and streams flowing out of them. The type habitat of the species is a thermokarst lake 500 m east of route Egvekinot – Iultin. It is a poorly known species that normally inhabits floodplain thermokarst and moraine lakes (fish kill lakes included), and from there may enter deep, slow streams. It lives in shelters beneath large stones, pieces of peat, and among aquatic vegetation.

Dallia delicatissima inhabits the freshwater lagoon, Pilkhykai (type habitat), in the region of Cape Dzhenretlen along the eastern coast of Kolyuchinskaya Bay, and a lake in the Eturveyem River drainage at the southwestern part of Kolyuchinskaya Bay. Lake Pilkhykai has no outflow and apparently freezes down to the bottom (Nordenskiöld 1881).

Chukot char (Salvelinus andriashevi) is endemic to Lake Estikhed, a closed lake near Providence Bay on the Bering Sea coast of the Chukotka Peninsula. The species is residential, and occurs near the bottom in sand pebble shallow waters and off the coasts of large fragmented ground. Its abundance is not known; apparently it is determined by total productivity of the ecosystem of the lake, and also the catch by fishermen.

Other noteworthy fishes

Alaska blackfish (Dallia pectoralis) is a typical freshwater fish that inhabits thermokarst and glacial lakes with muddy or large-stone bottoms. It sometimes migrates into streams, where it stays in pits with slow currents. It lives in shelters beneath large stones, hanging peat shores, and among aquatic vegetation. It may even freeze into the ice. This species is a typical representative of the fauna of ancient Beringia. 

The ecoregion also contains a local undescribed char from the Salvelinus alpinus group.

Ecological phenomena

The ecoregion is characterized by notable differences among species assemblages, depending on habitat. Rivers that have relatively rapid flow and are associated with foothills contain mostly Oncorhynchus species and an anadromous ecotype of dolly varden (Salvelinus malma). Rivers with relatively slow currents and a developed lake system around coastal plains contain assemblages of Siberian fish species. These are mostly resident and anadromous ecotypes of S. taranetzi, humpback whitefish (Coregonus pidschian), sardine cisco (C. sardinella), Thymallus, and burbot (Lota lota). Freshwater lakes of lagoon origin are normally separated from the sea by a sand spit. Species that inhabit lakes of this type include Salvelinus taranetzi, sardine cisco, and sockeye salmon (Oncorhynchus nerka). Natural dammed lakes (ultraoligotrophic water bodies) include only dwarf and normal ecomorphs of char (Salvelinus cf. alpinus, very slow-growing and long-lived, up to 38 years).

Justification for delineation

From an ichthyofaunal perspective, this is an unusual ecoregion that is characterized by a mix of North American, Pacific, and Siberian species. This ecoregion is the only one in the former USSR that supports the American genus Dallia and the species Bering cisco (Coregonus laurettae), Arctic grayling (Thymallus arcticus signifer), and pygmy whitefish (Prosopium coulterii). From an ecological perspective, it is characterized by severe climatic conditions, a lack of large and deep water bodies, and lesser streams and ponds that freeze to the bottom and lack any current in the cold season.

Level of taxonomic exploration

Hydrobiological studies are restricted by reconnoitring work carried out 20 years ago (Levanidov 1976). The major fishery studies were conducted earlier (Postnikov 1965). There are faunal reviews (Chereshenv 1991; 1998). Studies of the distribution and abundance of fishes were intensified, and scientifically substantiated measures of fisheries optimization were developed (Gudkov 1996a; 1996b).