Boundaries

The ecoregion encompasses the drainage areas of Anadyr’ River and adjacent rivers of Anadyrskiy Liman Bay. It also includes Lake Elgygytgyn.

The border with the East Chukotka [611] ecoregion (Chukotka Peninsula) stretches between the Kanchalan River drainage and rivers of Kresta Bay and the northern coast of Anadyrskiy Bay. Further south, the border follows the ranges of the Chukotskiy [Anadyrskiy] Khrebet, which divides the Amguema drainage (in ecoregion 611) and headwaters of the Belaya and Tnyurer rivers (Anadyr’ tributaries). The eastern spurs of the Severnyy Anyu’skiy, Yuzhnyy Anuy’skiy, and Oloyskiy ranges form the border of the ecoregion with the Kolyma [609] ecoregion. The southwestern border follows the southern slopes of the Anadyrskoye Ploskogor’e Upland and northern slopes of the Koryakskiy Range, which divides the Anadyr’ and Bol’shaya drainages with rivers of the Koryakia [612] ecoregion.

Freshwater habitats

The Anadyr’ River headwaters are steep, fast-running mountain streams. Middle and lower parts of the Anadyr’ River have former floodplain riverbeds. Thermocarst, glacial, and tectonic lakes are also numerous, with bog areas around the lake shores of thermocarst and glacial lakes. The Lower Anadyr’ River is impacted by tidal currents.

Rivers of the Anadyr’ drainage are characterized by spring floods (June) and by rain floods in August and September. Water temperature is low, reaching 13-14 °C only in July and August in the middle and lower reaches. By early October temperatures are at their minimum values, when ice cover is established. Ice thickness may be 140 cm, lasting 220-250 days. The average annual air temperature over the ecoregion is negative.

Lake Elgygytgyn is frozen 9.5-10 months a year, and sometimes the ice does not thaw at all. The thickness of ice reaches 2 m. The water temperature in summer at the shoreline does not exceed 6-7 °C. In June, under the ice the water temperature is 2.0-2.2 °C at a depth of 100-155 m. Water transparency is high and reaches 40 m, and mineralization is extremely low. Summer temperature stratification does not occur because of long winter cooling and permanent mixing of the water by strong winds. The climatic conditions are severe and are comparable to the conditions of Lake Hasen (Canada), the northernmost known water body inhabited by fish.

Terrestrial habitats

The ecoregion is comprised primarily of two terrestrial ecoregions: Chukchi Peninsula tundra along the northern border and Bering tundra throughout most of the ecoregion. The Kanchalan, Belaya, Tanyurer, Lower Anadyr’ and Velikaya rivers lie in the tundra zone with many of lakes and sphagnous marshes. The Middle Anadyr’ and Main rivers lie within the forest-tundra subzone, where arboreal vegetation is associated mainly with river valleys. The Upper Anadyr’ River falls within the northern taiga subzone, characterized by sparse deciduous forests and meadows in river floodplains.

Description of endemic fishes

Long-finned char (Salvethymus svetovidovi) is an endemic genus and species. Hhowever, its generic status is doubtful; in terms of phylogenetic methodology it may fall within the genus Salvelinus. As a locally distributed endemic taxon it was included in the Red Data Book of the Russian Federation (2001). The fish is a highly specialized non-migratory deepwater bottom dweller that inhabits Lake Elgygytgyn’s slope at a permanently low temperature. It is most abundant at depths between 50-100 m, and feeds only on zooplankton. It is a source of food for Boganida char (Salvelinus cf. boganidae). There is an opinion that Salvethymus svetovidovi is one of the most ancient representatives of salmonid fishes, phylogenetically close to a hypothesized ancestral form of chars of the genus Salvelinus.

Small-mouth char (Salvelinus elgyticus) is also endemic to Lake Elgygytgyn. It feeds on zooplankton similar to long-finned char, and also prefers deep water (up to 100 m). However, it displays some migrations, and approaches the shores on still nights. It is included in the Red Data Book of the Russian Federation (2001). The species is considered to be the most specialized species in the genus Salvelinus.

Other noteworthy fishes

Common whitefish (Coregonus anaulorum) is a near-endemic species in the Anadyr’ River drainage, rivers of the Anadyr’ Liman, and rivers of the Sea of Okhotsk coast of Koryakia. It is a relict of the common Anadyr-Penzhina river system, which had flowed during the pre-Pleistocene into the Sea of Okhotsk.

Boganida char (Coregonus boganidae, an undescribed Coregonus cf. boganidae) is found in lakes Elgygytgyn, Baran’e, and Pennoye (in the upper reaches of the Belaya and Tanyurer rivers), where it appeared relatively recently. In Lake Elgygytgyn it eats planktivorous long-finned and small-mouth chars. This fish has experienced heavy declines due to overfishing.

Ecological phenomena

Anadyr’ fishes demonstrate high ecological plasticity and adaptability to low water temperatures, prolonged ice cover, and a relatively weak food supply. Characteristic phenomena include distant upstream migrations of anadromous salmonid fishes such as chum salmnon (Oncorhynchus keta) and dolly varden (Salvelinus malma), and also coregonid fishes such as sardine cisco (Coregonus sardinella), common whitefish (C. anaulorum), and humpback whitefish (C. pidschian). These are determined by the history of the drainage, namely by the transgressions of the sea that flooded the lower parts of the drainage for long distances during the Pleistocene.

Lake Elgygytgyn represents a rare example of an endemic simple fish assemblage consisting of two planktivorous species and one predator. According to data from 1994 (Chereshnev 1996), the lake was inhabited by 12,000 individuals (with a total weight of 17.35 metric tons) of the predator, and 60,000 individuals (with a total weight of 8.95 metric tons) of the zooplankton-eaters. Relative to the area of the lake (113.4 km²), the biomass of the fishes equals 2.33 g per m² (Chereshnev 1996), corresponding to alpha-oligotrophic water bodies (Kitaev 1984).

Justification for delineation

The ecoregion encompasses the drainage areas of the Anadyr’ River and adjacent rivers of Anadyrskiy Liman Bay. This ecoregion represents a unique example of coldwater Palearctic fauna that is relatively rich in species. Belonging to the Pacific basin, the Anadyr’ system contains some affinities with the Kolyma River from the Arctic. Both river drainages had temporary connections in their upper reaches, and the Anadyr-Penzhina ancient system served as a route for some representatives of Siberian fish fauna down to Kamchatka.

Lake Elgygytgyn is a unique natural phenomenon. The lake was created during the Pliocene, about 3-4 million years ago. Since then, the lake has formed an exclusive ecosystem where plant and animal communities adapted to severe conditions of the Arctic Plateau (the name of the lake is translated as “lake where ice does not melt”). Geographically, the lake belongs to the Anadyr’ ecoregion, but it deserves evaluation as a distinct ecoregion since its fauna is different, and is characterized by 50% endemism on the generic level and 66% endemism on the species level. The lake may serve as a model for studying fish communities in extreme arctic conditions.

Level of taxonomic exploration

Good. Besides some earlier studies (e.g. Kaganowskiy (1927-1928) provided an excellent collection of Anadyr’ fishes), there have been regular studies, observations, and expeditions conducted by the Magadan Branch and Okhotsk Branch of the Pacific Institute of Fisheries and Oceanology, and the Institute of Biological Problems of the North of the Academy of Sciences. A summarizing monograph was published (Chereshnev et al. 2001).