Boundaries

The ecoregion includes rivers of the Western Caspian coast from the Kuma to Samur River and small rivers in Azerbajdjan to the north of the Main Caucasus Ridge [north of Baku] (Sumgait [Sumqayitcay] River inclusive). In the northeast, the ecoregion is contiguous with the Volga [410] and North Caspian [453] ecoregions across the Chornyye Zemly Desert. Here, isolated lakes and marshes lie adjacent to the Kuma River drainage. This area also includes the Vostochnyy Manych River, which is now a partly dried and isolated drainage connected in its upper section with the Kalaus River (part of the Don River drainage). Further down, the ecoregion encompasses the upper reaches of the Kuma River, which flows from the Stavropol’skaya Vozvyshennost’ Upland. In the south the border follows the Main Caucasus Range down to its easternmost slopes at Baku (south of Apsheron Peninsula [Abseron Yasaqligi]).

Topography

The Kuma River begins in the foothills of the Caucasus at an altitude of approximately 2000 m above sea level, between the Kuban and Terek River drainages. The length of the Kuma River is 590 km, and its catchment area is 25,500 km².  

Freshwater habitats

The Kuma River is a shallow steppe river, with its flow formed mostly in the steppe zone. Its average annual water flow is equal to 13 m²/sec. As the river flows into the Caspian Lowland, its channel divides into a number of branches that empty into lakes; here, the Kuma is lost in reeds before it reaches the Caspian Sea. In years when the Kuma was particularly full (1886, 1898, 1921, etc.)  it disgorged part of its waters into the sea.

The Tersko-Sulakskaya lowland (Terek-Sulak Lowland) is situated in the southeastern part of the Terek—Kuma lowland. It is covered by sand and alluvium from the Terek and is indented by numerous branches, anabranches, and irrigation canals. It is the delta of the Terek, with its apex near the village of Novogladkovskaya.  Expanding in a peculiar pattern, the delta attains a width of 60 km, a length approximately 90 km, and an area approximately 6000 km², which is nearly half of the Volga River Delta.

The Sulak is formed from the confluence of the rivers Avarskoye Koisu and Andiiskoye Koisu, beginning at the glaciers of the northern slope of the Great Caucasus. The length of the river is 150 km, and catchment area is 13,400 km². Both the Avarskoye Koisu and Andiiskoye Koisu rivers are characterized by typical mountain features, and are distinguished by large slopes and high water volume. The Sulak River also retains features of a mountain river, although its slopes decline considerably. Only over short areas within its lower reaches does the Sulak River acquire a plain character of flow.

The Samur is the second largest river in Daghestan. It originates high in the mountains from glaciers whose total area is 13.1 km², or 0.3% of the river’s catchment area. The length of the river is 216 km, and catchment area is 4430 km². The Samur is a rapid mountain river flowing along the bottom of a ravine, its slopes reaching 10-30‰. In spring and summer the river abounds in water; during this time strong floods caused by intensive snowmelt, warm rains, and heavy showers in the mountains sometimes occur. The average annual intensity of flow is equal to 75 m³/sec. The Samur River delta and the lowland adjoining it is an accumulative plain up to the Derebentsky passage. The delta is a relatively wide billowy plain, dissected by estuaries of the rivers Gyulgerichai, Rubaschai, and anabranches of the Samur. The delta area is approximately 260 km².

The ecoregion also includes alpine lakes of the Great Caucasus. These lakes are small water-bodies of glacial moraine origin. Among these are karst lakes characterized by exceptionally great depth. These include the Golubye lakes (Tserik-Ken’, Pakhurei, Sherek-Yana, and others), their average depth reaching 290 m. The deepest lake of this group is Lake Kezenoi-Am, or Great Trout Lake [Bolshoye Forelnoye], which is 426 m deep.

As in the other Caucasian ecoregions, the upper part of the rivers are mountainous in character, the middle current is pronounced depending on the degree of development of foothills, and the lower reaches, particularly large rivers, have broad, partly swampy floodplains.

The Terek, Sulak, and Samur rivers and their tributaries are characterized by exceptionally high turbidity ranging from 2500 to 4000 g/m³, and in some areas exceeding 5000 g/m³. The maximum average annual turbidity, the highest among the rivers of the USSR, reaches 11,700 g/m³ (in the Aksai River, near Chogar-Otar); the maximum average monthly turbidity being 35,000 g/m³. Turbidity during floods attains extremely high values, 80,000—120,000 g/m³ (e.g. in the Sunzha River, a tributary of the Terek River).

The water regime of rivers, fed predominately by alpine snow, is characterized by a prolonged flood that begins at the end of March and lasts until the end of August. The maximum flow is observed in May through June, which suggests that snow rather than glaciers play an important role.

The Terek River is the second largest river of the Northern Caucasus after the Kuban River. Its length is approximately 600 km, and catchment area is 43,700 km². The average annual intensity of flow is equal to 350 m³/sec. The Terek begins in the mountains within the boundaries of Georgia, south of Kazbek. In the upper reaches from the river head up to Dzaudzhikau the river is mountainous in character. It flows for the most part within a ravine, its slopes reaching 40° or more. Daryal Pass, restricted by high, steep slopes, is particularly deep. In that area many mountain streams fall into the Terek. Downstream from Dzaudzhikau the Terek River expands into a foothill plain. Up to the confluence with the Malka River it flows among pebble alluvium, dividing into branches. In that area it is confluent with numerous deep tributaries, such as Gizel—Don, Ardon, Belaya, Urukh, Baksan and Malka, flowing down from the Great Caucasus. After the confluence with the Malka River the slopes decline abruptly. Up to the confluence with the Sunzhi, the Terek flows in a sandy—clayey channel with numerous islands, spits, and shoals. The lower Terek begins downstream from the outfall of the above tributaries where the channel is split into numerous tributaries and branches.

Terrestrial habitats

The plains of the eastern Northern Caucasus are occupied by herb – feather grass steppes. In the east these grade into dry feather grass steppes, sagebrush – saltwort semideserts, and sand semideserts of the Caspian lowland. On the northern slope of the Great Caucasus the succession of vegetation zones occurs with elevation: from the forest—steppe landscape in the foothills to the zone of large-leaved forests and subalpine meadows in its highest elevations. The present coastline is covered by semi-arid and arid floodplain vegetation, including marshy meadows of deltas and flooded areas, grass, and halophyte meadows in river floodplains, and sagebrush – bunchgrass steppes in the Kuma River drainage.

Communities of coastal and lowland forests are represented on the Tersko-Sulak lowland along the main channels of the Terek and Sulak, their branches, and the delta. These forests typically feed on underflow and subsoil waters, their close proximity provided by relief, as well as the presence of large and small rivers. Floodwaters also contribute to the humidification of soils in the area of coastal forests. Areas characterized by excessive humidity are occupied by lowland forests of Alnus barbata. At present, a large area of lowland forests within the Tersko-Sulak lowland has been deforested and converted for agriculture.

Description of endemic fishes

Terek barbel (Barbus ciscaucasicus) is the closest relative to Kuban barbel (Barbus kubanicus), but is clearly distant from the Transcaucasian Barbus species. It is a comparatively large barbel attaining a length of 500 mm (SL). It prefers foothill and mountainous sections of rivers and streams with gravel or stony bottoms. It migrates upriver and spawns in shallow tributaries in March-September.

North Caucasian longbarbel gudgeon (Romanogobio ciscaucasicus) is a well-studied species in terms of morphology, but has almost no data in terms of biology. It inhabits streams and river sections with a moderate current and gravel substrate. Its distribution, biology, and status of threats need clarification.

Kezenoi-am trout (Salmo ezenami) is a locally endemic trout native to Lake Kezenoi-am (formerly Eizenam, on the border between Chechnya and Daghestan). It occurs at 1870 m asl, with superficial outflow. Kezenoi-am is a mountain lake with a maximum depth of 74 m. It is about 5 °C below 20 m and 5-18 °C in the upper layers in summer, is covered by ice in winter, has high oxygen concentrations throughout its depths year-round, and low concentrations of plankton. The trout spawns in the lake close to underwater springs, and the large-size form probably migrates to tributaries. Two forms are known: small-size (adults 160-260 mm SL, 200-350 g) and large-size (adults 380-1130 mm SL, over 1 kg). Males mature at 2 years, females at 3 years. The spawning period extends over almost the whole year. Young juveniles feed mostly on gammarids and chironomid larvae; larger juveniles and adults feed on molluscs, benthic invertebrates, and fry; and the largest individuals are mostly piscivorous. The species is highly impacted by the introduction of Squalius cephalus, which feeds on its fry.

Terek nase (Chondrostoma oxyrhynchum), a near-endemic, is found in piedmont and mountain rivers with strong currents and rocky or gravel bottoms, but prefers microhabitats with slower currents rich with vegetation. It feeds mainly on detritus and periphyton algae. Juveniles also feed on benthic invertebrates. The Terek nase is markedly rarer than the barbel. It also occurs in the Kura-South Caspian Drainages ecoregion [434].

Ciscaucasian spined loach (Sabanejewia caucasica), another near-endemic, is found in streams 3-10 m wide and less than 1 m deep in foothills and plains, sometimes in irrigational canals, usually on gravel, but rarely on sandy bottoms along precipitous banks. It also occurs in the Kuban ecoregion [428].

Other noteworthy fishes

Krynicki’s loach(Barbatula merga) is endemic to this ecoregion (Kuma, Terek, Sulak, Shura-ozen and Samur drainages) and the Kuban drainage [428]. It inhabits the upper mountainous reaches of rivers.

The upper Terek drainage historically played a major role in the reproduction of Salmo trutta ciscaucasica. Spawning areas were situated in the tributaries within the upper reaches of the Terek River, including the rivers Baksan, Malka, Urukh, Ardon, Sunzha, Ass, Argun, etc. Due to hydraulic construction, the natural reproduction of salmon in the Terek River stopped, and its large stock yielding up to 450 tons per year was lost.

Ecological phenomena

The dispersal of fishes within the ecoregion is pronounced among vertical zones. In the alpine zone sea trout (riverine form of Salmo trutta ciscaucasica) and its relative, S. ezenami,in Lake Kazenoi-Am, are found. In lower mountainous sections (down to the foothill zone), apart from trouts, other, mostly rheophilous species appear (such as genera Squalius cephalus, Barbus, Chondrostoma, Barbatula). In the lower reaches the fauna differs by the presence of mostly phytophilous species, which are typical inhabitants of slow-flowing rivers and stagnant waters. Many of these are migratory, semi-migratory, or euryhaline.

Justification for delineation

This ecoregion is one of four Caucasian ecoregions that is clearly different by its composition of true riverine fish fauna. Geographically it belongs to the northern Caucasian slope and overlaps with drainages of the Caspian Sea basin.

 

Level of taxonomic exploration

Fair