Boundaries

The ecoregion includes the drainage of Lake Baikal.

Topography

The lake occupies the largest central trough in a series of tectonic breaks of the Baikal Rift Zone in Eastern Siberia. It is divided by underwater sills into three main basins: the southern basin (max. depth 1432 m), central basin (1632 m), and northern basin (897 m).

Freshwater habitats

Water of the lake is characterized by extreme mineralization, not more than 100 mg l^-1, and exceptional poverty in calcium, not more than 15 mg l^-1. The oxygen saturation of water even at maximum depths is never below 70-80%. Water transparency in the summer ranges from 5 to 8 m, and in open areas in the winter may attain 30 – 40 m.

The thermal regime of the lake is rigid, subject to seasonal fluctuations in only the upper 200 – 250 m layer of water. The temperature throughout the year in deeper parts of the lake is permanent and equal to 3.3 – 3.6 ºC. During the summer the surface temperature does not exceed 14 – 16 ºC, but at  depths of 10 m it is 10 – 12 ºC, and in shallow bays it may warm up to 20 – 24 ºC. During the year two periods of temperature stratification are noted – direct in summer and reverse in winter. There are also two periods of homothermy – in spring (May – June) and autumn (October – November) when the temperature of all water layers are similar and approximately equal to 4 ºC due to currents, wind, and thermal mixing. Freezing of the lake occurs annually in January – early February depending on weather characteristics. The duration under ice is approximately 4 months when the ice thickness is 60 – 80 cm to 1.2 – 1.5 m. The opening of the lake from ice occurs in the southern part of the lake between 1 – 10 May, and in the northern part between 25 May – 10  June.

Storm winds are common for Lake Baikal at the end of summer and in autumn. The maximum wind velocity on the lake is recorded in April, May, and November, with minimums in February and July. Eighty percent of summer storms fall in the second half of August and September. The height of waves in the middle hollow of Lake Baikal approaches 4-4.5 m, and 22º steep.

Terrestrial habitats

Lake Baikal is surrounded by mountain ridges that are extraordinary natural formations. The mountain – hollow relief comprises two types of mountain ranges. The variable humid Baikalian and arid Transbaikalian affect the complexity of the biogeography and bioclimates, with very abrupt transitions (observed nowhere else in Siberia) in space from dry steppe to taiga and mountain-taiga landscapes.

Description of endemic fishes

It is commonly considered that fishes of the suborder Cottoidei in Baikal are represented by two endemic subfamilies, Cottocomephorinae and Cottinae, and two endemic families, Comephoridae and Abyssocottidae. However, the taxonomic rank of Cottocomephorinae, Comephoridae, and Abyssocottidae is too high if based on phylogenetic data (see review in Bogutskaya & Naseka 2004).

Endemic genera inlcude Abyssocottus, Asprocottus, Cottinella, Limnocottus, Neocottus, Procottus (Abyssocottidae); Batrachocottus, (Cottocomephoridae); and Comephorus (Comephoridae). Cyphocottus and Cottocomephorus are near-endemic. Around 30 species are endemic.

Other noteworthy fishes

Taxonomic revisions suggest that two subspecies (Thymallus arcticus baicalensis and Thymallus arcticus brevipinnis) within the Thymallidae family should in fact be two distinct species inhabiting the Baikal basin and other parts of the Yenisei drainage.

The major historical object of fisheries in Lake Baikal was Baikal omul’ (Coregonus migratorius), although its yields have declined abruptly in recent years. Artificial breeding is currently being conducted. In Lake Baikal it forms three races: pelagic, coastal, and near-bottom deepwater. Which area it inhabits is characterized by locations of breeding and feeding migrations and characteristic features of growth and feeding. For reproduction it migrates to tributaries of the lake. The pelagic race reproduces primarily in the Selenga River during two peaks of spawning migration in September and October. The coastal race spawns mostly in tributaries of northern Baikal, Verkhnyaya Angara, and Kichera, and also in the Barguzin River. The peak of the coastal race’s spawning migration occurs in late September. Fishes of the near-bottom deepwater race migrate for spawning mostly into rivers that drain into Posolsky Sor ("sor"=shallow bay), into some small tributaries in other regions of Baikal, and also into the Selenga and Barguzin rivers.

Ecological phenomena

The ecosystem of Lake Baikal is close to ocean ecosystems in structure and other characteristics. Characteristic features include: 

1. Presence of a pelagic community of organisms, characterized by low species diversity and high productivity. The basis of abundance and biomass of mesoplankton (up to 0.64 g m^-3 in productive years and less than 0.25 g m^-3 in years with low production) is formed by the crustacean Epishura; the basis of macroplankton (up to 3 g m^-3) is formed by endemic Gammaridae.

2. Pelagial ichthyocenosis is comprised of secondary pelagic viviparous fishes, Comephorus baikalensis and C. dybowski. Other near-bottom pelagic sculpins include Baikal yellowfin (Cottocomephorus grewingkii) and longfin Baikal sculpin (C. inermis), and also the main commercial fish species of the lake, Baikalian omul’ (Coregonus migratorius).

3. The presence of zones of high productivity of macroplankton in the near slope area (above depths of several hundred meters), analogous to highly productive upwellings in oceans.

4. The benthic community is characterized by extraordinary species diversity and high productivity (up to 30 g m^-2 in open littoral and up to 80 g m^-2 in bays), consisting mostly of oligochaetes, mollusks, amphipods, and chironomids.

5. Presence at great depths (more than 1000 m) of freshwater deepwater fauna; its analogues are only known in seas and oceans.

All non-cottoid fishes of Lake Baikal are confined to waters < 350 m deep. All cottoid fishes may be classified into three ecological groups: benthic, benthopelagic, and pelagic species. The benthic cottoids are divided into three bathymetric groups: 1) coastal shallow water species in depths up to 150 m; including species from the genera Leocottus, Paracottus, Batrachocottus, and Procottus; 2) eurybathic species that inhabit a wide range of depths between 100-1000 m during their lifespan; including species from the genera Asprocottus, Cyphocottus, Limnocottus, Batrachocottus; 3) deepwater (abyssal) species that are restricted to depths from 400 to 1600 m; including Abyssocottus, Cottinella, Neocottus. It is peculiar that the peak of species diversity in Lake Baikal has shifted to greater depths. Twenty-two species permanently inhabit depths over 300 m or spend some stages of their life there.

Justification for delineation

Lake Baikal stands apart from other freshwater bodies in that it is a freshwater analogue of a sea. It contains a highly specialized fauna, including the highest number of endemic genera and species in northern Eurasia. The endemic cottoid fishes demonstrate a unique complex of morphological adaptations to pelagic and deepwater habitats.

Level of taxonomic exploration

Very good. Limnological Institute, Russian Academy of Sciences, and Ulan-Ude (Buryatia).