Boundaries

The ecoregion encompasses the whole Kura-Aras catchment (Lake Sevan exclusive) and rivers of the Caspian Sea in southeastern Azerbaijan, as well as the lower reaches of rivers (Kyzyluzen [Safid Rud]) eastward to the Taran River (exclusive). In the north, the border of the ecoregion follows the main divide along the Caucasus Range; and in the west, the  ecoregion follows the western slopes of the central Caucasus and Likhskiy [Likhs K’edi], Meskhetskiy [Meskhet’is K’edi], and Arsianskiy [Arsianis K’edi] divide ranges. In the south, it coincides with the Araxes watershed, and further to the south is contiguous along the Talyshskiye [Talish = Kuhha-ye Tavalesh] and El’ Burs mountains.

Topography

The Suramsky Range divides the river network of the Transcaucasia into two unequal parts: an eastern and a western one. Rivers of the eastern part occupy 90% of the Transcaucasian territory and belong to the Caspian Sea basin, whereas rivers of the western part belong to the Black Sea basin (ecoregion 433).

The Kura River is the largest river of the Transcaucasia and of the Caucasus in general. It begins in Turkey in the swampy Kars region and empties into the Caspian Sea south of the Caucasus. The length of the river is 1515 km, and its catchment area is 188,000 km². 

In the upper reaches, up to Tbilisi, the Kura River flows mostly among ravines and gorges, alternating with intermontane depressions and plains. The best known are Borzhomskoye Gorge, where the river is pressed within a narrow corridor over 55 km, and Mtskhetskaya Ravine. The banks of the Kura’s valley are formed by volcanic rocks that are resistant to erosion. From Tbilisi up to Mingechaur the Kura flows along the plain, and only in some places its channel is narrowed by rocks. Near Mingechaur (downstream from the estuary of the Alazan) the Kura River cuts through the Boz-Dagh Range. There it flows in the gorge, forming the Mingechaur rapids. Further downstream the river expands into the wide Kura-Araks lowland, finally emptying into an estuary. In this area the river channel is somewhat elevated above the terrain. However, during high water the river overflows, forming new channels and horseshoe-shaped lakes known as “akhmazy” (a local name that means “does not flow”).

The river network in the upper part of the Kura River drainage is well developed, and fed by a number of tributaries. The largest of these are Liakhva, Ktsiya-Khrami, and Aragva, among others. All of them are of mountain character, flowing in deep gorges and often forming waterfalls.

In the middle and lower reaches the Kura River flows through the extensive arid lowland, and thus receives few tributaries. The majority of them do not reach the river channel because their waters are extracted for irrigation. Part of the left coast tributaries empty their floodwaters into the Kara-Su Depression, which is the ancient channel of the Kura River that parallels it for approximately 100 km. The main tributaries of the Kura River are the Araks and Alazan rivers.

The Alazan is 410 km in length, and its catchment area is 16,900 km². From the left side it receives a great number of tributaries flowing from the Main Caucasus Ridge. These rivers abound in water and never run dry. The few right tributaries flowing down the Kakhetin Ridge are turbulent flows in spring and dry ravines in summer. In the lower reaches for more than 100 km the Alazan does not receive a single tributary from the right. The drainage of the Alazan River poses the greatest threat of mudflow in the Caucausus. Its largest tributary is the Ioru (Iora) River.

The Araks [Aras, Araxes] River is the main tributary of the Kura, flowing into it from the right near the estuary. Its catchment area is 102,000 km², and its flow (240 m³/sec) is nearly half of the total flow of the Kura near the estuary. The Araks River begins in Turkey, and over most of its length is a frontier, separating the USSR from Turkey and Iran. In its lower reaches the Araks flows within the boundaries of the USSR. The length of the river is 1070 km. The river annually discharges approximately 16 million tons of suspended alluvium. As it flows from the mountains into the Milskaya steppe, the erosion activity gradually fades and is replaced by accumulation. There the river deposits its alluvium and wanders throughout the steppe, frequently changing its channel.

A major tributary of the Araks is the Razdan (Zanga) River. Its length is 146 km, and catchment area is 7310 km². Flowing out of alpine Lake Sevan, the Razdan is a relatively short river with a high slope equal to 1089 m. Of the other large tributaries of the Araks, the Western Arpa-Chai (lenth 205 km, catchment area 9700 km²) and Eastern Arpa-Chai (126 km and 2600 km²) are notable.

In the Kura-Araks Lowland in the area of intensive irrigation are numerous small water bodies; the majority of those are fed by surface floodwaters of the Kura, and also by waters discharged from irrigation systems.

Many lakes are situated in the lower reaches of the Araks. Some of them arose as a result of the Araks floods and thus contain freshwater. Others are lake-swamp water bodies. The largest lake is the Akh-Chala, formed in the past century as a result of the Araks flood.

Rivers of the Lenkoranskaya (Talyshskaya) lowland begin on the slopes of the Talyshskii [Talysh] Ridge and are relatively short. Many of those do not reach the sea and, overflowing over the low plain, swamp it. Others, trapped by belts of sand and pebble formed by sea surf, discharge their waters into shallow lakes called “mortso” or “murdab”, which means dead water. The largest streams are Vilyazh-Chai and Lenkoran-Chai.

Lake Sevan is one of the largest alpine fresh water bodies in the world, and the largest in Armenia. It is situated in the northeastern part of Armenia in the Sevan Depression at an altitude of 1898 m above sea level. The lake is tectonic in origin, and its shape is reminiscent of a triangle. The Artanishsky Peninsula and the Noraduzsky Cape divide it into two parts: Malyi Sevang and Bolshoi Sevang. Twenty-eight small rivers flow into the Sevan, and the Razdan River only flows out of it. From the north, east, and southeast Lake Sevan is bounded by the Lesser Caucasus Mountains and Areguninskii, Sevanskii, and Zangezurskii ridges; from the west and south it is bounded by mountains of the central volcanic region of the Transcaucasia, and Vardenisskii and Gegamskii ridges. The water volume in the lake declined considerably, by more than 42%, during the years after the drawdown began for hydropower engineering.

Freshwater habitats

The Kura is fed by melting snow, partly by melting glaciers in the mountains, and also by rains. The annual variation of the level spring flood is pronounced, covering the first half of the summer; in the remaining part of the year the level is low. During heavy rains notable water rises are sometimes observed. A large amount of suspended alluvium makes water of the Kura River extremely turbid. After strong rains in the drainages of its left-coast tributaries, waters of the Kura River acquire a grey-chocolate color, whereas rains in the Akhalkalakskoye Upland, which was formed by Tertiary yellow clays, result in the yellow color of its waters. The average annual turbidity of water of the Kura River is equal to 1660-1950 g/m³. The maximum turbidity during the flood period reaches 50,000 g/m³. The total discharge of suspended alluvium carried by the Kura to the estuary is 36,300,000 tons per year. With such a notable discharge of suspended matter, the delta of the Kura River is rapidly expanding, advancing 65 m into the sea on average each year.

The region of Lake Sevan is characterized by northern and southwestern winds, which mixes the water surface layer, and in shallow areas, the entire water column to the bottom. The lake bottom consists of sand, silty sand, grey and black silts, and crystals of potassium carbonate.

Terrestrial habitats

Plateau-shaped elevations of the Lesser Caucasus are occupied by different types of alpine meadows, steppes, and semi-deserts. The extensive Kura-Araks lowland is for the most part an arid steppe, grading into a halophyte semi-desert in the east.

Description of endemic fishes

The ecoregion contains one endemic genus, Leucalburnus, and one near-endemic genus, Acanthalburnus.

Leucalburnus is monotypic, including only L. satunini, which is found in mountainous streams and some lakes in the Aras drainage in Turkey. It is known only from several specimens, but the morphological examination confirms a distinctive nature of the genus. Special studies are needed to evaluate the state of threats.

Acanthalburnus is near-endemic to the ecoregion, and includes the blackbrow bleak (A. microlepis).  It is also represented by A. urmianus in lake Urmia [Orumiyeh=Reza’iyeh]. This lake, now endorheic, historically belonged to the Kura drainage system. So, the genus is an endemic genus of river systems connected in its origin with eastern drainages of the Caucasian Mountains.

Acanthalburnus belongs to the tribe Abramidini and shows clear affinities to Acanthobrama from the Near East, South Turkey, and Tigris-Euphrates. This provides good evidence of the Caucasian-Asian links. The blackbrow bleak (A. microlepis) is a typical riverine fish that prefers streams with moderate to fast currents and pebbly-stony bottoms, as well as mountainous lakes. It is distributed in the upper and middle reaches of the Kura River, with tributaries downstream to Mingetchiaur, as well as in the Aras River downstream to Karadonly (Azerbaijan). It mostly feeds on zoobenthos and plant detritus. It was a non-abundant fish in 1960-1980s, but no reliable data at present.

Kura bleak (Alburnus filippi) is widely distributed in the Kura-Aras basin in the rivers of Lenkoran’ Province and Safid Rud [Kyzyluzen]. In Kura and Aras it is spread from the headwaters to the lower reaches through tributaries. It is known from lakes Cildir in Turkey and Arpilitsh in Armenia (Dadikian 1986), both of which are located over 3000 m above sea level. It prefers lakes and stretches of streams that have a relatively slow current, sandy-rocky bottom, and are rich with algae and benthos. Alburnus atropatenae is a close species in Lake Urmia.

Gokcha barbel (Barbus goktschaicus)  is an endemic species of Lake Sevan. The abundance of the barbel declined abruptly because of water drainage from Lake Sevan. As a result, it was included in the Armenian SSR Red Data Book.

Romanogobio macropterus is a species close to the Kura gudgeon (R. persus) from Lake Urmia, but deserves separate status due to differences in some anatomical characteristics.

Pseudophoxinus atropatenus and P. sojuchbulagi are both restricted endemics. Pseudophoxinus atropatenus is only known from the type locality, which are small marshy rivulets and springs in the Turian-chay river system (Kura tributary) among a relict forest in the Kutkashenskiy region of Azerbaijan. There is currently no data on the recent state of the species, and no specimens in museums. This species may represent one of the most threatened species of the Caucasus. This species needs further investigation. Pseudophoxinus sojuchbulagi is only known from springs of the Soyukhbulag River system (Kura tributary) in the Akstafa region of Azerbaijan. It prefers fast running water and rocky bottoms.

Orthrias araxensis and Barbatula brandti are poorly known species; their taxonomic status and exact distribution needs further studies.

Mursa (Barbus mursa) is a peculiar barbel with no clear affinities in the genus. It is characterized by a thick, three-lobed lower lip and a strong, markedly serrated ray in the dorsal fin. It is the typical species of the fast-running waters of the upper and middle sections of the Aras and Kura rivers. It is rarely found in smaller rivers of the coast eastward to Safid Rud. Its recent status is not known.

The fish fauna of Lake Sevan is represented by the polymorphic endemic species of Sevan trout (Salmo ischchan). It includes four ecological races — winter ishkhan, summer isjkhan, gegarkuni, and bodzhak — which are frequently regarded as subspecies (Salmo ischchan ischchan, Salmo ischchan aestivalis, Salmo ischchan danilewskii, Salmo ischchan gegarkuni). Formally this is not correct. If races of ishkhan are placed in separate taxa, they should be regarded as separate species (this opinion has not been published yet).

Other noteworthy fishes

The contains endemic subspecies, such as Seven khramulya (Capoeta capoeta sevangi),  Chondrostoma oxyrhynchum cyri, Rutilus rutilus schelkovnikovi, Blicca bjoerkna transcaucasica, and Barbatula tigris cyri.

Seven khramulya (Capoeta capoeta sevangi) is a lacustrine derivate of the mostly riverine C. capoeta capoeta. Some authors consider them as conspecific with C. capoeta gracilis from rivers of the South Caspian coast. All three subspecies/forms represent a typical benthic dweller that feeds on periphyton. They have a specifically modified lower jaw covered by a sharp horny layer and prefer clear, well-oxygenated water, and rocks covered with algae. The Seven khramulya is highly endangered.

Ecological phenomena

Vertical zoning among species is similar to the other Caucasian ecoregions. Most endemic forms are true freshwater, and mostly rheophylic, species that occur in the upper sections of rivers and their tributaries.

Justification for delineation

The Kura-South Caspian Drainages ecoregion covers all areas draining to the southern Caspian, from the Sumqayit River basin in the west to the Taran River in the east. It covers the largest area in the Caucasus River system that represents all possible ecological zones from mountains to the plain. This ecoregion should probably be divided into smaller units, but too little is known about species distributions.

This ecoregion is considerably different from the ecoregions to the north. Its rich ichthyofauna lacks such widely distributed northern elements as Thymallus thymallus, Leuciscus leuciscus, Leuciscus idus, Phoxinus phoxinus, Gobio gobio, Barbatula barbatula, Misgurnus fossilis, and Cottus gobio. At the same time, the southern genera Capoeta and Pseudophoxinus are present. The Kura-South Caspian Drainages fauna contains a high number of endemic taxa and taxa distributed further to the south. There is one endemic genera, Leucalburnus (L. satunini), and one near-endemic genera (also in Lake Urmia), Acanthalburnus (A. microlepis, a near-endemic species). Two highly restricted local endemics from the genus Pseudophoxinus (P. atropatenae, P. sojuchbulagi) represent a very isolated section of the genus range (Turkey; the Near East). There are other endemic species or those locally distributed in rivers of the Southern Caspian basin (to Sefid-Rud), such as Romanogobio macropterus, Chondrostoma cyri, Barbus mursa, Alburnus filippii, Barbatula brandti, and Neogobius cyrius, plus several endemic subspecies.

Level of taxonomic exploration

Fair