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410: Volga - Ural

Major Habitat Type:

temperate floodplain rivers and wetlands

Author:

Nina Bogutskaya

Countries:

Kazakhstan; Russia; Caspian Sea

Boundaries:

The ecoregion includes rivers and lakes of the Volga, Ural, and Emba drainage areas within Russia and Kazakhstan. The borders of the ecoregion strictly follow the watersheds.

The northern border of the ecoregion (shared with the Barents Sea Drainages ecoregion [407]) starts in the east from the Ural Range at about 62º N and extends westward along the natural divide of the Severnyye Uvaly Hills (Volga and Kama headwaters to the south, and Vychegda and Pechora rivers (within ecoregion [407]) to the north. To the west of the Severnyye Uvaly Hills, the northern border follows the Galichskaya Vozvyshennost’ Upland, and then follows the watershed of the Sukhona River and Lake Vozhe [ecoregion 301]. The border next moves northward along the southern slopes of Undomskaya Vosvyshennost’ Upland to include the Kema River drainage (with lakes Kovzhskoye and Kemskoye). In the northwest, the border between the Volga-Ural ecoregion and the Lake Onega - Lake Ladoga ecoregion [409] runs along the Andomskaya Vozvyshennost’ Upland, the southern part of the Megorskaya Gryada Range, Vepsovskaya Vozvyshennost’ Upland, and Tikhvinskaya Vozvyshennost’ Upland. Further south, the border crosses the Valdaiskaya Vozvyshennost’ Upland and includes the Shlimo, Seriomo, Seliger, and Vselug lakes. The Bel’skaya and Smolensko-Moskovskaya Uplands divide the drainage areas of the Daugava [404], Dnieper [425], and Volga rivers. The Srednerusskaya Vozvyshennost’ and the southwestern spurs of the Privolzhskaya Vozvyshennost’ divide drainage areas of the Oka River, Volga reservoirs, and Don River [427]. In the northwest, the Ergeni Upland divides the Kuma drainage (Sarpinskiye lakes) and the Volga River. Further, the border crosses sandy waterless areas of the Prikaspiiskaya Nizmennost’ [Precaspian] Lowland to meet the main course of the Volga just upstream from its delta [453]. In the northeast, the border follows the formal border of the Emba drainage along the northern margin of the Miortvyy Kultuk Sor [453], and then extends northward along the Chagray [Shaghyray Ustirti] Plateau and Mugodzhary Mountains [Mughalzhar Tauy]. This is the southernmost range of the Urals that divides the ecoregion from the Irgiz [Yrghyz] [601] and Ob’ drainage area [602] up to about 62º N (the divide between the Vishera (a Kama tributary) and Pechora [407] rivers.

Drainages flowing into:

Caspian Sea (closed lake; West Asian endorheic basin)

Main rivers or other water bodies:

The main rivers in the ecoregion include the Volga, Ural, and Emba. Tributaries, lakes, and reservoirs of the upper Volga include: Tvertsa, Vetluga, Mologa, Sheksna, and Sviyaga rivers; Piros, seliger, Sabro, Vselug, Volgo, Beloye, Kubenskoye, and Nero lakes; and the Ivan’kovskoye, Uglichskoye, and Rybinskoye reservoirs. Within the Middle Volga are the rivers Kostroma, Unzha, Oka (an extensive drainage area in the western part of the Volga catchment), Vetluga, Kama (an extensive drainage area in the eastern part of the Volga catchment), Sok, Samara, Bol’shoi Irgiz, and Eruslan; and the Cheboksarskoye, Gor’kovskoye, Kamskoye, Kuibyshevskoye, and Saratovskoye reservoirs. The lower Volga includes the Volgogradskoye reservoir, Akhtuba, Bol’shoi Uzen, and Malyy Uzen’ rivers, Kamysh-Samarskiye Ozera lakes, and the Volgo-Akhtubinskaya Poima floodland. Tributaries, lakes, and reservoirs of the Ural [Zhayyq] River include Lake Chelkar, Kushum River, Kushumskiye lakes, Yaik River, Sakmara River, Or’ River, Kumak River, Kumak Reservoir, Iriklinskoye Reservoir, and Sagiz River. The main tributary of the Emba [Zhem] River is the Temir River.

Topography:

The Volga River basin occupies approximately ¼ of the East European Plain. It comprises approximately 70% of the active drainage of the Caspian Sea, but provides more than 75% of the total inflow into it. The eastern left shore of the drainage joins the Ural Mountains, where the Kama River, the main tributary of the Volga River, originates. The Oka and its tributaries originate in the Central Russian Upland; the Sura, Sviyaga, and Moksha rivers originate in the Volga Upland; and the Tsna River originates on the Tsna Plateau. The density of the river network varies throughout the Volga River drainage. River flow is greatest in the upland areas of the Sura and Sviyaga drainages, whereas the lightest river flow occurs in the lower reaches of the Volga River, on the Caspian Lowland.

Most of the rivers of the Volga River drainage that begin at low elevations (not exceeding 200—300 m above sea level) are of plain character; their slopes are often only several cm per 1 km. Larger slopes are characteristic of tributaries of the Volga River that begin on the western slopes of the Ural Mountains, where they have the appearance of mountain rivers. Larger slopes are also characteristic of the upper reaches of rivers of the Volga Upland and Central Russian Upland. For example, on the Chusovaya River the average slope in the upper reaches is 120 cm per 1 km; in the upper area of the Belaya River, 160 cm per 1 km; on the Sura River, 87 cm per 1 km; and on the Oka (the part from the river source up to Orel), 75 cm per 1 km. Rapids sometimes occur where rivers cross moraine ranges. The majority of the rivers, however, are characterized by slow currents, shoals, rifts, and meandering river channels. Floodplains of strongly meandering rivers are rich in lakes and oxbows (e.g. Oka, Moskva, Sura, Kostraoma). The valleys are most often asymmetrical, with high right coasts and low left ones. A large part of the drainage of the Upper Volga is occupied by swampy lowlands, such as Mologo-Sheksninskaya, Kostromskaya, Balakhninskaya, Meshcherskaya, and others.

Freshwater habitats:

The Volga basin is divided into four major sections, including the Upper Volga, Middle Volga, Lower Volga, and delta. The Upper Volga is defined by some authors as extending from its source in the Valdai Hills to the confluence of the Sheksna River (approximately where the Volga exits Rybinsk Reservoir). The lower border of the Middle Volga is the dam of the Volga GES (Kuibyshev Reservoir), although before impoundment the border of the Middle Volga was delineated at the confluence of the Kama River, the greatest left tributary of the Volga. The Lower Volga, whose lower boundary is at the Volga “Lenin” Dam impounding the Kuibyshev Reservoir, comprises the Saratov and Volgograd reservoirs, and the Volga Akhtuba floodplain. The delta is within the Volga Delta-Northern Caspian Drainages ecoregion [453].

The Volga River drainage includes numerous lakes. In the upper reaches are groups of lakes like Seliger, Sterzh, Penno, and Volgo; in the middle reaches are lakes Nero, Pleshcheevo, Galichskoye, and Chukhlomskoye. Downstream from Volgograd, among numerous branches and former riverbeds, are floodplain lakes. In the Caspian Lowland are Sarpa lakes, which in deep water years are connected with the Volga River through the Sarpa River during spring floods. Lake Beloye, with an area of 1125 km2, is the largest body of water of the Upper Volga drainage. It is smaller than the area of the Pskov—Chudskoe water body (approximately 3600 km2), nearly equal to that of Lake Ilmen (1124 km2) (both in the Central and Western Europe ecoregion [404]), and is five times larger than the area of Lake Seliger (221 km2), one of the large water bodies of the Upper Volga. The drainage area of Lake Beloye is a weakly hillocky, afforested plain, surrounded on its periphery by moraine ranges. These moraine ranges, being watersheds, separate the drainage of the Caspian Sea from the neighboring drainages of rivers belonging to the basins of the Baltic Sea and the White Sea.

The Kama is the largest and most powerful tributary of the Volga River. With a length of 2030 km and a catchment area of 522,000 km2, it is among the important rivers of the European USSR. The Kama originates within the Upper Kama Plateau, which is the northern part of the High Zavolzhiye Upland. The upper part the river flows north, then turns east at a right angle, and having reached the foothills of the Ural Mountains changes directions again, turning abruptly to the south. Thus, in its upper reaches the Kama seems to form a giant loop. Although its total length exceeds 2000 km, the straight distance from its headwaters to its estuary is only around 445 km. Glaciation, which influenced the formation of the river network, is said to be responsible for the peculiar course and abrupt changes of the Kama River.

The Oka River is a right tributary of the Volga River that merges with it near Nizhni Novgorod, 2361 km upstream from the Volga River estuary. Its major tributaries are the Moskva River (length 502 km, drainage area 17,500 km2), the Moksha River (614 km, 50,900 km2) and Klyazma River (547 km, 42,200 km2). With a length of 1478 km and drainage area of 245,000 km2, the Oka is second in length and drainage area after the Kama among the tributaries of the Volga River. The Oka River begins in the Central Russian Upland at an altitude of 226 m above sea level and flows northward for approximately 400 km. After the confluence with the Ugra River it turns east and retains its general direction, even though it strongly meanders. After it reaches the Meshcherskaya Plain only its right shore remains high; the left shore is generally low, having only a few high areas. For example, between Kasimov and Yelatma, where the Oka crosses limestone of the Oka-Tsna swell, the height of the left shore reaches 87 m. The width of the Oka River valley increases gradually from 0.5 km in the upper reaches to 25-30 km in the middle reaches, downstream from the confluence with the Moskva River.

The character of the Oka River valley and river channel is sharply divided into two parts: the upper part from the river source to its confluence with the Moskva River, and the lower part including the remaining length of the river. In its upper reaches the river passes through the Central Russian Upland, where it has a deeply indented (40-65 m), mostly narrow river valley and slope from 0.2-0.3 to 1.0-3.0‰ (in the uppermost part) that is quite notable for a plain river. Downstream from the confluence with the Moskva River, the Oka River enters the area of the extensive Oka lowland (Meshcherskaya Plain), abounding in swamps and lakes, and reminiscent of Belarus Polesye. Its valley widens considerably, attaining a width of 25-30 km in some lake-like extensions. Numerous hilly chines occur in the wide floodplain of the Oka River; lower areas between them are occupied by bayous, backwaters, and oxbow lakes. Shoals and rifts are frequent in the river channel.

The Ural River is 2428 km in length, and is the third largest river in Europe after the Volga and the Danube. Its drainage area is 231,000 km2; including the closed drainage of the Ural – Emba interfluve, the area increases to approximately 400,000 km2. From close to the river source it is of plain nature, which is unusual for a river originating in the mountains. For most of its extent the Ural flows in a relatively wide valley. The Ural River is fed mostly by right tributaries flowing from more elevated parts of the drainage. The largest of these is the Sakmara River (798 km in length) and its tributary, Bolshoi Ik (345 km in length). The density of the river network in the drainage varies, with the river network most developed in the drainage of the Sakmara River. In the middle part of the Ural River drainage, its density is two or three times less than the Sakmara River drainage, and downstream from the confluence with Chaga and Barbastau the Ural River has no permanent tributaries. In contrast to all other rivers of the Ural River drainage, the Sakmara River and its tributaries remain unregulated, representing a standard of a little changed river system.

Another large tributary of the Ural River is the Or River, with a length of 332 km and drainage area of 18,600 km2. The Or River is a typical steppe river with a pronounced peak during spring tide, comprising 95% of the total annual flow (averaging 534,000,000 m3). Spring tide on the Or River is turbulent, but short. The river quickly returns to its shores and already in June becomes very shallow, disintegrating into separate deep reaches connected by transparent streams with sandbanks, backwaters, and beaches. The River Ilek flows into the Ural from the left, 200 km downstream from Orenburg. It has a catchment area of more than 41,000 km2, the largest compared to all Ural River tributaries. The length of the river is 623 km, and annual flow is 1,320,000,000 m3/year. The floodplain is abounding in numerous anabranches and bayous. Ilek floodplain lakes – Burannoye, Golodnoye, Novoiletskoye, and Lebyazhye – with an area of 30 to 100 ha each, are among the deepest and largest in the Ural River drainage.

The main characteristic feature of the Ural River is the extremely uneven flow between years, as well as within a year. The difference between the years may be as large as 10-fold. Average annual flow of the Ural River at the Kushumskii gauging station is 10.6 km3, but in spring this figure increases many-fold. Nevertheless, the Ural River is sufficiently full, and has freshwater throughout its extension. The flood level in spring depends prmarily on the thickness of the snow cover and intensity of snowmelt in spring. In years with a snowy winter and favorable spring, the spring flood is full and the floodplain is inundated 7—8 km, and in some areas (Ilek River) up to 18 km. Water covers the floodplain for around a month, and then a gradual decline in the level of floodwaters takes place. In the years with little snow in winter and a short, hot spring snow melts quickly and a large part of the meltwater is absorbed by the soil. As a result, the spring flood may be so small that a large part of the floodplain is not covered by water. The low spring flood negatively affects the spawning conditions of freshwater (fluvial, pure riverine) fishes of the Ural, which is aggravated by water-temperature fluctuations. Fluctuating temperatures also negatively affect egg-laying and further development of eggs, even in years with high floods. The Ural River floodplain is rich in lakes, particularly in its middle current. The winter hydrochemical regime of these lakes depends to a large extent on the spring flood.

A number of small rivers flow in the interfluve Ural – Volga. Noteworthy among these are Bolshoi Uzen and Malyi Uzen, their drainages situated within the limits of the Obshchii Syrt. As they flow into the Caspian Lowland they form a labyrinth of Kamysh – Samara lakes.

Rivers situated between the Ural and Emba, having reached the Caspian Lowland, gradually loose their valleys and flow through flat and broad lowlands with a very small slope. In spring these valleys are filled with slowly running waters, which are then discharged into wide depressions forming swampy and saline land overflows.

The Emba River headwaters rise from the slopes of the Mugodzharek Mountains at an altitude of approximately 350 m above sea level. The length of the Emba River is 712 km, and drainage area is 40,400 km2. The river is poor in water and is fed almost exclusively by snow. More than 95% of its flow occurs from April to May, and in spring the Emba River contains a large amount of alluvium. After rains the river becomes turbid and is a muddy-milky color. In summer it includes a number of separate reaches with ditchwater.  The average river flow of the Emba River 152 km from the estuary is 17.5 m3/s, which is 23 times lower than the Ural River. The Emba River restricts the Ural – Emba drainage from the south and serves as a boundary between Europe and Asia. Until the middle of the 20th century, approximately 20 km from the sea the Emba River formed a delta with three major branches: Kara-Uzyak, Kiyan, and Kulok. At present the Emba River does not reach the Caspian Sea, but is lost in salt marshes.

Lying to the east, the Sagiz, a former tributary of the Emba River, is now drying in its upper and lower reaches. The length of the Sagiz is 551 km, drainage area is 19.4 km2, and average river flow near the estuary is 2 m3/s. A large number of salt lakes with a total area up to 3000 km2 are situated in this area, east of the lower reaches of the Ural River up to the Emba River estuary. In the Sagiz River estuary are extensive muds, the so-called Tentyak-Sory, flooded by the river’s spring tide. Tentyak-Sory are typical maritime formations of the Caspian Lowland. Here, one can see gradual transitions of ilmens into sors, salt-marshes, and salt lakes.

The majority of rivers of the Ural – Emba region have no tributaries. Beach ridges are quite common along the river channels, which give these streams the appearance of channels hampering the outflow of floodwaters into the valley. Extensive tides are common in the lower reaches of the river  where floodwaters stay. In this area are distinguished river meadows in three levels: high, middle, and low. By the beginning of the summer secondary streams and water bodies already dry out. In the summer the flow ceases for the majority of rivers, and they split into separate reaches with stagnant and, often, brackish water. Groundwater also becomes saline. After the fall of the rivers’ water level, floodplains are overgrown by meadow vegetation. In the lower reaches of rivers with shallow lakes, extensive spring floods and humid meadows provide suitable nesting areas for water fowl.

Other tributaries of the ancient Khvalyn Sea, such as the Uil, Kaldygaity, Buldyrty, and Olenti, also do not reach the Caspian Sea. As recently as several hundred years ago the Uil was a recent tributary of the Ural River. The length of the Uil is 800 km, and the drainage area is 31.5 thousand km2. The lower reaches of the Uil are situated in the Caspian Lowland. Here the river divides into several branches, some of them lost in Taisoigan sands, forming huge overflows. The main channel of the Uil River passes between sand ranges of Taisoigan and Biiryuk, and ends in Lake Aktobe.

The Kaldygaity begins after the confluence of the Kuagash and Bayana streams, originating in the steppe of chalk mountains. The length of the river is approximately 200 km, and the drainage area is 2500 km2. The Akkymy sands begin in the valley of the Kuagash River. In the southwest the Kaldygaity divides into two sand ranges – Karagandykumy and Kuguzyukkumy – emerging from them 45 km before the Ural, where it is lost in a system of lakes and high waters. The Buldyrty flows parallel to the Kaldygaity approximately 45 km west of it. Its length is approximately 120 km. In spring these rivers, as well as the Olenty River, flow into the extensive and flat Baiguttin Lowland, but seldom flood up to the Ural.

Terrestrial Habitats:

Physico-geographic conditions of the Volga drainage are varied. Its catchment area is situated in the center of the East European Plain, between approximately 60° and 50° N and 32° and 60° E in forest and forest-steppe zones. South of 50° N the lower Volga crosses steppe and semi-desert regions of the Caspain Lowland. The drainage of the Volga River is situated mostly in the plain territory, but it includes also a number of uplands representing outer and inland watersheds.

The Ural River drainage is situated mostly at the junction of the dry steppes of Europe and semi-deserts of Middle Asia. This reflects the pronounced continental character of the climate, which becomes even more pronounced in the south. The moderating influence of the Caspian Sea only extends to the narrow coastal zone. Maximum precipitation falls in July, only in Orenburg and Guryev in June, with minimum precipitation in February. The Ural River drainage is characterized by  low precipitation. The upper reaches of the Ural and Sakmara rivers and their tributaries lies in the foothills zone of  of the eastern slopes of the Urals, characterized by complex relief with heterogenous soil and vegetation cover.

Relief of the Bolshoi Ik drainage is diverse. The Upper Bolshoy Ik and the network of its small tributaries are situated at an altitude of 400—600 m in mountains covered by pine and mixed forest. To the south forests occur only along the river channel, gradually turning into thickets of willow shrubs, and disappearing completely in the lower reaches of the Ural. From Orenburg southward the main elements of the landscape are plateau and hilly plains, which are strongly eroded in some areas. Southward, steppe is replaced by a desert landscape with sagebrush and saltwort brushwood. The majority of left tributaries of the Ural are typical steppe rivers flowing down the slightly sloping Ural – Tobolsk watershed, Mugodzhar Mountains (Or River), and the low Ural – Ilek watershed. Inn the summer some of them become saline.

The Emba River originates among dry steppes of the Poduralye. Further downstream the river passes between chalk ranges, Aktolagai and Shirkal and others, and gradually loses its water crossing semi-deserts and deserts of the Caspian Lowland. The Ural-Emba drainage area is characterized by meadow oases amidst semi-deserts and deserts of the Caspian Lowland.

Fish Fauna:

The native fish fauna includes over 65 species from 16 families. Although the fish fauna is rather large, it almost lacks endemic fishes.

The construction of dams and reservoirs strongly influenced all of the ecological groups of fishes. The anadromous forms - Caspian lamprey, shads, sturgeons, inconnu - lost most of their natural spawning sites. Their persistence, in the case of sturgeons and inconnu, strongly depends on artificial reproduction. All of the anadromous sturgeon species and Caspian salmon (Salmo trutta ciscaucasicus) were recorded in the beginning of the century in the Upper Volga, but disappeared after the construction of impoundments, and Caspian salmon was last observed in the tailwaters of Rybinsk Reservoir in 1954. In the post-impoundment Volga, most notable was the appearance of a new pelagic biotope, whereas river floodplains were replaced by lacustrine littoral and sublittoral biotopes. Typical riverine fish habitats remain only in the upper reaches of tributaries and in the forewaters of dams, and account for no more than 1% of the total surface area. Populations of obligate rheophilic fishes such as sterlet (Acipenser ruthenus), dace (Leuciscus leuciscus), chub (Squalius cephalus), undermouth (Chondrostoma variabile), and gudgeon (Gobio gobio and Romanogobio albipinnatus) either adapted to reproduce in channels with intense current, diminished rapidly following reservoir construction, disappeared completely, or have persisted in small reserves in tributaries or in the tailwaters of dams. Typical limnophilic species, which lived previously in water bodies of the Volga floodplain, also lost their habitats since they were unable to adapt to great changes of the water level.

Conversely, the formation of new biotopes improved living conditions for rheo-limnophilic and limno-rheophilic fishes adapted to reproduce in slow currents or standing waters using plant and tree remnants as a spawning substrate. With the construction of reservoirs a new pelagophilic guild has developed. Before, pelagic fishes were poorly represented in the ichthyofauna of the Volga. The migration cycles of these species are independent of the littoral zone, occurring primarily in the water column over the sublittoral and profundal zones. These species include sublittoral psammophilic spawners with demersal eggs (e.g. smelt, cisco, and burbot), and pelagophilic spawners, whose eggs develop while drifting within water column circulation patterns (e.g. sabrefish). Thus, changes in the abundance and distribution of nearly all Volga species have taken place. For example, there has been a clear reduction in the distribution of about 25 species within the Volga basin, with an increase in area for less than 10 species.

The Ural and Emba sub-ecoregion is quite similar to the Volga, being principally different in its much lower number of species due to the absence of most southern forms (e.g. Rutilus frisii, Alburnus chalcoides, both Barbus species, Vimba vimba) and the absence of originally marine eurybiont gobiids due to much less developed deltaic water bodies. The most distinguishing feature of the Ural River was the fact that it served as the main spawning river for the fringebarbel, or shyp, sturgeon (Acipenser nudiventris). The Ural has not been extensively dammed, and it is the only major river still used for sturgeon (shyp and beluga) spawning migrations.

In endorheic drainages of the Ural-Eba area, species such as tench (Tinca tinca), northern pike (Esox lucius), roach (Rutilus rutilus), and ide (Leuciscus idus) inhabit deepwater reaches of drying rivers and their floods that are unstable in both time and space.

Description of endemic fishes:

The Volga whitefin gudgeon (Romanogobio albipinnatus) is a typical benthic gudgeon inhabiting moderately flowing lowland rivers that prefers sand substrate and clear, well-oxygenated water. It occurs in the Volga and Ural rivers, and probably also in the Emba River.

The Belozero cisco (Coregonus vessicus) is a local endemic native to lakes Belozero (Lake Beloye), Vselug, and Seliger in the Upper Volga drainage. It was commonly considered as a subspecies or a form of "ryapushka" (Coregonus albula). Since 1943 is has become invasive in the Upper and Middle Volga reservoirs downstream to Saratovskoye Reservoir. Large-sized ryapushka from Lake Pleshcheevo (former Pereslavkoye) in the same group of lakes may represent a distinct species as well.

The freshwater tyulka (Clupeonella tscharchalensis) is considered by some authors (Kottelat, Freyhof, in press) as a distinct species through its relationships with marine Caspian and Pontic tyulkas, C. caspia and C. cultriventris. It occurs in pelagic zones of large freshwater lakes and reservoirs having been spread upstream since the damming of the Volga and Kama rivers.

Other noteworthy fishes:

Belorybitsa (Stenodus leucichthys), or Caspian cisco, has been commonly considered to be conspecific with the northern cisco (Stenodus nelma). It is a large (up to 1300 mm SL) migratory fish. Before the construction of dams, its migration route was over 3000 km long, reaching the uppermost reaches of the Ufa and Belaya drainages (Kama tributaries). Historically, migrations from the sea to estuaries began during autumn and ended nearly a year later. Mature adults entered the Volga River, but only a few individuals entered the Terek and Ural rivers. Spawning occurred during September-October when water temperatures are below 6°C. Although adults migrate back to the sea soon after spawning, many die. Due to the loss of spawning grounds, native stocks are reportedly extinct and survival depends exclusively on stocking. In Volga all spawning grounds were above the Volgograd Dam. In 1959 only a few spawners remained. Up to 33 million (1988) juveniles were stocked during Soviet times. However, between 1996-1999 only 600,000 juveniles were stocked, resulting in another drastic decline in the spawning population.

Black-back shad (Alosa kessleri) forages in the Caspian Sea from where adults ascend the Volga River (only a few fish enter Ural and Terek) to spawn. It historically travelled upriver to the Kama and Oka systems. It enters rivers with unripe gonads. Some shads spawn 2-4 seasons, but most females die after spawning. Spawners appear at the coast in March-April, entering rivers when the water temperature reaches about 9°C, in late April and early May, with a peak at 12-15 °C. Spawning runs originally lasted 30-50 days. The fish begin spawning when the water temperature rises above 15°C in May-August, as long as the temperature remains between 15-23 °C. Damming on the Volga significantly reduced available spawning sites and migration routes. All populations declined during the first decades of the 20th century; the decline seems to have continued due to heavy overfishing. Most spawning grounds were upriver of Volvograd and are no longer accessible. There is an opinion (Abduralhmanov et al. 2002) that the species has been already extirpated.

Volga shad (Alosa volgensis), similar to the black-backed shad, ascends the Volga River to spawn. But in contrast to the black-backed shad, it does not penetrate far upstream, and enters the rivers with ripe gonads. In the Volga River it spawns between the delta and Volgograd, 150-200 km from Nikolskoye to Raygorod. Females spawn 2-3 times in their life. It appears at the Volga delta in April, and enters the river when the water temperature reaches about 9°C in late April-early June, with a peak at 17°C. Its spawning run lasts 3-8 days. Spawning starts when water temperatures exceed 13°C in late April-June as long as the temperature remains below 27 °C.

Six species of sturgeons inhabit the Caspian basin. The most abundant is the Russian sturgeon (A. gueldenstaedtii) (60%). Much lower in abundance are the starry, or stellate, sturgeon (A. stellatus) (30%) and beluga sturgeon (Huso huso) (10%), and very low stocks of starlet (A. ruthenus), fringebarbel sturgeon (A. nudiventris), and Persian sturgeon (A. persicus).

The extensive spawning areas in the rivers flowing into the Caspian Sea, as well as the large food supply in the water body itself, favored the formation of the world’s largest stock of sturgeons. Each sturgeon species has a complex population structure, and the populations are associated with separate spawning areas. At present there are at a minimum 20 reproductively isolated populations of sturgeons in the basin. However, only the Volga populations of starry sturgeon, Russian sturgeon, and beluga sturgeon retain their commercial importance, as well as Ural populations of beluga sturgeon and starry sturgeon, which lends particular significance to this ecoregion. Fisheries are actually based upon two species, starry sturgeon (Volga and Ural species) and Russian sturgeon (Volga population), comprising not less than 85% of the total yield of Caspian sturgeons.

Starry, or stellate, sturgeon is represented by three populations from the Volga, Ural, and Kura rivers. Fishes of Volga origin are predominant in the Caspian Sea. The stock of Ural starry sturgeon is second in abundance. The Volga River is most important in the reproduction of starry sturgeon. As a result of the regulation of flow of the Volga River, only 372 ha (11%) have remained of the previous spawning area (3390 ha). Starry sturgeon uses 248 ha of estuary spawning areas. In the Ural River, the starry sturgeon uses 845 ha (over 75%) of the total remaining natural spawning area (1100 ha).

The Russian sturgeon is now represented by two populations, one from Volga and one from Ural, and two season races, in spring and winter. The Ural population of the Russian sturgeon declined, until recently, due to excessive fishing. As a result, the ecological niche that had become vacant was occupied by the Volga population. In 1989, the portion of Volga fishes was 75%. This, however, was not enough to increase the number of Russian sturgeon in the Ural River. Today, there are 22 functioning spawning areas comprising a total area of 372 ha in the Volga River; in the Ural River sturgeon spawning areas comprise 226 ha. Within other rivers of the drainages there is practically no natural reproduction of sturgeon. The efficient spawning of sturgeon depends on complex factors: the determining factors are water level of the river during the flood, and the number of spawners that reach spawning areas. In recent years there has been an abrupt decline in the reproduction level of sturgeon in the Volga River due to the extremely low number of spawners that reach spawning areas, as well as the deterioration of their physiological state.

Ecological phenomena:

The Caspian Sea is a vast and highly productive brackish water basin. Its northern rivers form a unique system for the life cycle of anadromous fishes. Because of their immense area, the Volga and Ural river networks had many areas suitable for spawning, thus providing the opportunity for dispersal among different fish populations, and also the opportunity for reproductive success. Nearly all anadromous species had winter and spring races, which allowed populations to migrate into rivers at different times and remain for different periods depending on the length of their migration routes. Unfortunately that system has now been completely destroyed.

Evolutionary phenomena:

The most interesting phenomenon is the establishment of intraspecies groups in anadromous and semi-anadromous fishes due to microevolutionary processes related to the separation of populations for feeding and, particularly, for spawning.

Justification for delineation:

The ecoregion includes river drainage areas and lakes of the Volga, Ural and Emba drainages, as well as some endorheic basins that formerly belonged to the same drainage system. This ecoregion, being very large, is naturally delineated by drainages characterized by the commonness of their paleohistory and the former interconnections between them. In the north and northeast, it is bordered by the Main East European divide that separates the drainages of the Arctic and Central Asia from the rivers that drained to the Ancient Caspian Basin. Thus, the ecoregion overlaps the whole hydrographic system of the Pre-Caspian Depression, which was highly modified by transgressions and regressions of the Caspian Sea and events of the glacial epochs, especially of the Dnieper Glacial epoch 260-240 thousand years ago. Although the fish fauna is rather large, there is only one strictly endemic species in the Volga catchment, Romanogobio albipinnatus. However, this ecoregion is quite peculiar from an ecological point of view. Before damming it supported a unique, highly diverse system of populations and so-called ecological forms (races) of migratory – anadromous and semi-anadromous – species.

Level of taxonomic exploration:

Good

References/sources:

Abdurakhmanov, G. M., Karpyuk, M. I., et al. (2002). "Modern state ad factors which determine biological and landscape diversity of the Volga-Caspian region of Russia" Moscow: Nauka.

Bogutskaya, N. G.,Naseka, A. M. (2004). "Catalogue of agnathans and fishes of fresh and brackish waters of Russia with comments on nomenclature and taxonomy" Moscow: KMK Scientific Press.

Poddubnyy, A. G. (1978)"Fish fauna" In Butorin, N.V.;Mordukhay-Boltovskoy, F.D. (Ed.). Volga and its life. (pp. 228-247) Leningrad: Nauka.

Slyn'ko, Yu V., Kiyashko, V. I., et al. (2000)"List of cyclostomata and fishes of the basin of River Volga" In Yakovlev, V.N. (Ed.). Catalogue of plants and animals of water bodies of Volga drainage. (pp. 252-277) Yaroslavl': Institute of Inland Waters Biology of RAS.

Yakovlev, V. N. Slyn'ko Yu V. Kiyashko V. I. (2001)"Annotated catalogue of cyclostomata and fishes of the Upper Volga basin" In Yakovlev, V.N. (Ed.). ecological problems of Upper Volga. (pp. 52-69) Yaroslavl': Institute of Inland Waters Biology of RAS.

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