Acipenser gueldenstaedtii, Brandt & Ratzeburg, 1833

Taxonomic description of species

Body fusiform, dark colored, frequently with yellowish shade. Mouth transverse, lower lip interrupted. Gill membranes attached to isthmus. Dorsal scutes 9-18, ventral scutes 7-12. Gill rakers 19-29. Head and snout relatively short.
Intraspecific forms. Specimens of Russian sturgeon sampled from different Caspian rivers have similar characteristics as regards their morphometric and plastic features (Peseridi, 1986). A.V. Pavlov and G.A. Elizarov (1967) subdivide the stock of North Caspian sturgeon into 2 local groups: the Volga and Ural group.
Russian sturgeon in Azov sea basin differs with relatively short head; sturgeon in the Northwestern part of the Black sea - with somehow shortened and tapered snout (compared with sturgeons in the sea of Azov and Dnepr river).
Related forms. Other species of genus Acipenser.

 Distribution of species within the Caspian

The species is widely distributed throughout the whole area of the sea. The main feeding areas are located in the North Caspian and shelf zone of the Middle Caspian. In the South Caspian increased aggregations are registered at the Turkmen shelf and the areas of volcanic shoals (Ulskogo, Gryazny Vulkan). No considerable accumulations are revealed in the eastern part of the Middle Caspian as well as at the western coast of the South Caspian.
Status as per International Red Data Book. IUCN Red Data List - EN.
Status as per National Red Data Books. Azerbaijan - EN; Iran - EN; Kazakhstan - EN; Russia - EN; Turkmenistan - EN.
First record for the Caspian. Brandt, 1833.
Redescription of species. Berg, 1911; Holcik, 1989.

General characteristics of species

Ecologo-taxonomic group. Nekton
Origin. There is no consensus of opinion regarding the origin of sturgeons. R. Miller (1969) considers that genus Acipenser as well as genera Polyodon and Scaphirhynchus emerged at the territory of North America (Mississippi river). According to Birstein and De Salle (1998), Acipenseriformes originated in the Central Asia, Tethys Sea basin.
World distribution. Ponto-Caspian endemic species. Inhabits the Caspian, Azov and Black seas.
Habitat. Changes habitats several times during life span. Early developmental stages occur in fresh river water, juveniles migrate to the sea where they grow until reaching maturity, and then enter the river to spawn. Sturgeon is primarily bottom dweller. Its distribution is confined mainly to sand or silt bottoms (Legeza, 1972). Avoids uncombined silt.
Migrations. Undertakes feeding and seasonal migrations within the Caspian, anadromous spawning and downstream post-spawning migrations Spawners enter the Volga River, less - the Ural River, insignificant number comes to the Terek and Kura.

Relation to abiotic environmental factors

Relation to salinity. Brackishwater euryhaline species, occurs both in freshened and typical Caspian seawaters (5.43-14.34 ⁰/₀₀) (Legeza, 1972)
Relation to temperature. Eurythermic species.
Occurs at wide range of seawater temperatures: 2.0-24.8⁰C; 2.0-4.0⁰C in winter, 6.0-8.0⁰C (March-April) in spring, 14.0-22.0⁰C (June-July) in summer, 12.3-12.8⁰C (October-November) in autumn (Legeza, 1972). Spawners enter the Volga river at water temperature 2-4⁰C, the peak of spawning run in the river is observed at maximum temperature of 22-27⁰C (Zhuravleva, 2000).
Vertical distribution. Euribathic species; occurs at depths 2-130 m; in winter - 10-40 m, in spring - 10-30 m. In summer Russian sturgeon migrates to the most trophic shallow areas of the sea with depths less 20 m, in autumn moves to depths up to 100 m (Legeza, 1972).
Relation to oxygen conditions. Resistant to hypoxia and anoxia. Found at conditions of oxygen deficiency at the bottom - 40.5% and over-saturation up to 133.1%.
Relation to fluctuations of the sea level. In the years of falling Caspian Sea level, sturgeon fingerlings, which migrated downstream the Volga and Ural rivers, moved directly to the western shelf of the Middle Caspian without lingering in the northern part of sea. In full-water years sturgeons are more widely distributed within the North Caspian that in the low-water years.

Feeding

Feeding type. Heterotrophic (holozoic)
Feeding behavior. The main part of sturgeon diet is composed of bottom organisms. In search of food sturgeon moves incessantly at the bottom, approaches food and tastes substrate with tactile and gustatory receptors located on barbels and lips. Since food item is detected sturgeon makes abrupt seizing-sucking movement with protractile oral apparatus.
Food spectrum. In the Volga river early sturgeon larvae feed on zooplankton - Daphnia, Bosmina, Cyclops. In the Ural river larvae consume benthic organisms as well: Oligochaeta, Polychaeta, Corophiidae, Gammaridae, Mysidae, larvae and pupae of Chironomidae. In the course of downstream migration fingerlings feed on bottom and near-bottom organisms: Gammaridae, Mysidae, Corophiidae, Oligochaeta, and Ampharetidae. At sea, the diet of sturgeon juveniles (41-80 cm TL) contains less minute crustaceans and Nereis, consumption of crabs and small fish increases at the same time. As sturgeon grows, it transfers to feeding, primarily, on mollusks, prevailing species - Abra ovata, representative of Mediterranean fauna introduced into the Caspian. Adult sturgeon is a benthophagous mollusk-eater. Its food spectrum changes depending on food supply and season.
Food supply. Sturgeon fattening is related mainly with benthos production in the Caspian sea. Status of sturgeon food supply in 1960-1970-s was regarded as satisfactory due to increased biomass of Syndesmia (Abra ovata). By the year of 1976, in the period of sea level decrease, a reduction of areas with high benthic production: was observed: at the borderline North and Middle Caspian, Dagestan coast, eastern coasts of Middle and South Caspian. In 1980-s, the period of rising sea level and stabilized salinity, rich food supply was formed to provide for sturgeon feeding at sea. Since early 1990-s, development of food supply for sturgeon in the North Caspian tend to decline.
Quantitative characteristics of feeding. Food consumption rate - N/A
Index of stomach fullness in fingerlings (total Wt - 1 g) from the Ural river varied within 154-238⁰/₀₀₀, in the Volga river - 123-478⁰/₀₀₀, respectively. Relative daily diet of fingerlings (Wt - 1-2 g) amounted to 16-20% when fed on chironomids, 10.6% - on gammarids, 20% - on mysids (Stygar, 1984). Mean index of stomach fullness in fingerlings (TL - 4-7cm) from the Kura river was 116⁰/₀₀₀. The values of this index in fingerlings captured at sea decreases gradually from 198⁰/₀₀₀ in juveniles 10 cm TL to 62⁰/₀₀₀ in fish 40 cm TL, which is related to transition to food with high nutritive values.

Reproduction

Reproduction type. Sexual
Reproduction areas. Before regulation of the Volga river stream, sturgeon spawners migrated as far as to the upper districts - to Cherepovets, Yaroslavl, Kostroma, up to Murom in the Oka river. After construction of HEPS (hydroelectric power station), since 1959, Russian sturgeon spawns at stony ridges of riverbed located below Volgograd city (Vlasenko, 1982). In Akhtuba tributary spawning occurs in the area upper to Kapustin Yar. In the Ural river spawning sites are situated at the distance 65-1,000 km from the river mouth (Peseridi, 1986). Prior to regulation of the Kura and Araks river, sturgeon spawning sites were situated 660 km (Mingechaur), and 330 km (Karadonly), respectively, from the river mouths. At present, only single sturgeon spawners enter the rivers Terek, Sulak, Kura, and Araks.
Terms of reproduction. In the Volga river spawning occurs in May and June, in the Kura - from the last 10 days of May till early June. Similar to the other anadromous sturgeons, vernal and hiemal races are distinguished within this species (Berg, 1934).
Fecundity. The absolute fecundity of Russian sturgeon in the Volga river did not exceed 300,000 eggs (196,000-284,900) prior to 1979. This value increased gradually to the maximum of 366,800 eggs in 1991, and then declined to 213,300 eggs in 1999, which is attributed to respective increased and decreased proportion of females of senior age groups in these periods (Zhuravleva, 2000). Mean fecundity of sturgeon in the Ural river was 323,900-310,700 eggs in recent years; fecundity of Russian sturgeon from the Terek river - 198,000-217,000 eggs (Musaev, 1972).
Spawning interval was estimated as 4-5 years for males, 5-6 years for females by A.T. Dyuzhikov and E.V. Serebryakova (1964); according to data of A.V. Pavlov and G.A. Elizarov (1967) minimum spawning interval is 2-3 years for males and 3-4 years for females.
Limiting factors.

• Hydrological conditions during spawning period (May-June);
• Number of spawners accessed to the spawning grounds;
• Predation on eggs, larvae and fingerlings;
• Pollution of the water body.

Life history and development

Life history stages. Russian sturgeon passes in the course of development several life-history stages characteristic of all sturgeon species: embryo, prelarva, larva, fry and adult fish (Detlaf, Ginzburg, Shmalgauzen, 1981).
Relation to environmental factors. A system of favorable factors of aquatic environment (with certain magnitude of fluctuations) is needed for normal development. These factors are as follows: temperature, oxygen conditions, pH, flowage, and excluded contamination (specifically, oil pollution).
The most vulnerable to abiotic and biotic factors are certain embryonic and early larval stages (up to transition to active feeding).
Age of maturity. Russian sturgeon matures at the age of 7 (males) - 8 (females) years old. In recent years, the youngest mature fish registered in the catches from the Volga and Ural rivers are aged 8 (males) - 10 (females) years.
Thermal conditions of development. Water temperature within the range 9-21⁰C is favorable for maturation and embryonic development of all sturgeon species (Detlaf et al., 1981). In the Volga river development of sturgeon larvae occurs at 14-25⁰C, fingerlings grow at 20-25⁰C. In the North Caspian areas with water temperature 20-24⁰C are preferred by sturgeon juveniles.
Quantitative characteristics of growth.

Linear and weight growth of Russian sturgeon assessed from trawl catches in the North Caspian in 1967
(Pavlov, Zakharov; 1971)

Growth equations for mature sturgeon of the Volga river are as follows:
Males: Y= 0.47x - 32.8 - 0.0007x²,
Females: Y= 0.3x - 25.6 - 0.0001x², where
Y - age, years
x - total (absolute) length, cm.

Structural and functional population characteristics

Sexual structure. Population structure of Russian sturgeon at sea is characterized by long-term dominating of females (50.7-71.8%). In spawning populations males prevail in junior age groups, females - in senior groups due to extraction of early-maturing males with commercial catches. In late years, proportion of females estimated in catches from Ural river, was 33.5-31.8%, 17.3-13.8% in the Volga river, respectively.
Age- size structure. The maximum specimen age of sturgeon captured at sea - 47 years old. The mean age of sturgeon from the North Caspian was estimated to be 8 years old (in 1999). Specimens aged 46 years old occurred in the Ural river, aged 40 years - in the Volga river. Females aged 15-20 years, males aged 12-15 years predominate in the Ural river catches; in the Volga river - 16-21 and 12-18 years old, respectively.
Mean TL of females from the Volga river was 143.5 cm, males - 123.8 cm in 1963; 148.1 cm and 124.6 cm, respectively, in 2000. Maximum mean values for females were recorded in 1993 - 163.8 cm, in 1983 for males - 135.9 cm. Maximum average TL of females captured at sea was recorded in 1977 - 134.2 cm, males - in 1979-1980 - 115.5 cm. In 1999, average size of sturgeon in the Caspian Sea reached the minimum of 88.6 cm.
Quantitative characteristics. According to survey data relative characteristics of sturgeon abundance in the North Caspian amounted to 1.52 spt (specimens per trawl) in 1981-1985 (Slivka et al., 2000); they decreased to 0.73 spt in 1986-1990; and further - to 0.68 spt in 1991-1995; 0.46 spt in 1998. In summer of 1999, sturgeon concentrations in the eastern part of the North Caspian almost tripled as compared with respective values for summer of 1998. At the same time, the number of sturgeons feeding at Dagestan coast of the Middle Caspian decreased by a factor of 9.5 (0.25 spt).
Population trends. The total (absolute) abundance of Russian sturgeon in the Caspian Sea declined to 29.2 million specimens in 1999, as compared with 60.5 million specimens in 1978. Commercial reserve reduced from 546,600 tons to 104,000 tons, respectively (Khodorevskaya et al., 1997; Slivka et al., 2000).

Interspecific relations

Interspecific competition during feeding at sea appears between Russian sturgeon and those fish species with coincident food spectrum - gobies, stellate sturgeon, and beluga. In 1970-s, increased coincidence in food spectrum of sturgeon and cyprinids (Caspian roach, bream) was revealed in regard to such food items as sprats and gobies.

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. Valuable commercial fish species
Commercial characteristics of species, catches. Over the period of 1962-1975, sturgeon catches in the Volga-Caspian region were sustained within 5,400 (in 1970) - 9,000 (in 1963) tons. In the next 13 years (save for 1986), annual catches exceeded 10,000 tons, with registered peak in 1981 - 13,510 tons.
In the year of 2000, 251 ton of sturgeon was harvested.
The maximum catch (from rivers) in Kazakhstan was recorded in 1978 - 550 tons. In 1962 and 1964, they exceeded 200 tons (260-250); in 1965, 1969, 1989-1993 - ranged within 110-190 tons; in the other years catches were less 100 tons; in 2000 - 54 tons.
In Azerbaijan sturgeon catches constituted 230-300 tons in the years 1962-1964, 1978-1979; 30-180 tons over the period of 1980-1999; 44 tons in the year of 2000.
Fishing gears and fishing zones. Since 1962, fishing of Russian sturgeon has been transferred to the rivers of the basin. Sturgeons are harvested with river beach seines. Special sturgeon fishing at the Volga river was prohibited starting 1996. Following the Order #219, 20 July, 2001, sturgeons are used only for purposes of research and hatchery reproduction.

Impact of fisheries on the population status

The population of Russian sturgeon of the Caspian Sea was subjected to intensive commercial exploitation in the periods of 1931-1940, 1951-1962. Fishing at the rivers (1962-1981) led to moderate removal from the population, its abundance and biomass were underused. New system for fishing management was set up in 1981; harvesting increased considerably, which later resulted in decline of spawning population (number and biomass) and, consequently, reduced scope of natural reproduction. Beginning early 1990-s, the decisive factor in sturgeon abundance became illegal fishing/ poaching.
Human impact/Threats. 

• Regulation of river streams.
• Poaching.
• Contamination of aquatic environment.

Conservation measures:
1. Artificial/ hatchery reproduction was initiated in mid-1950-s to compensate for HEPS construction (damming).

Number of Russian sturgeon fingerlings released from the hatcheries of the Caspian basin (except for I.R. Iran), mln. specimens

2. Fisheries regulations introduced:

• A ban on sturgeon fishing at sea (including Russian sturgeon) in 1962;
•  A ban on special sturgeon fishing in the Volga-Caspian basin in 2000.

3. Measures required for future:

• Sign agreements between Russia, Iran, Azerbaijan, Kazakhstan and Turkmenistan on joint exploitation, protection and reproduction of sturgeon stocks;
• Enhance the scope of natural and hatchery reproduction.

References

Berg, L.S. 1911. Fauna of Russia and adjacent states. Fish. Vol. 1. S.Petersburg. 250 p.
Berg, L.S. 1934. Spring and winter races of migratory fish. USSR AS Press. 5: 711-732.
Berg, L.S. 1948. Fish of fresh waters of the USSR and adjacent countries. Part 1. Moscow-Leningrad. 468 p.
Birstein, V. J., De Salle R. 1998. Molecular phylogeny of Acipenseridae. Molecular phylogenetics and evolution. Vol. 5, 1: 141-155.
Brant, J.F. 1833. In: Brandt, J.F., Ratzeburg, J.T. Medizinische zoologie. Berlin. Bd. 2. S. 11-13.
Detlaf, T.A. A.S. Ginzburg and O.I. Shmalgauzen, 1981. Sturgeon development. Nauka Press. Moscow. 224 p.
Dyuzhikov, A.T. and E.V. Serebyakov, 1964. Some features of ecology and duration of the sex cycle in the Volga River sturgeons. VNIRO Proceedings. Vol. 56, 3: 105-115. Moscow.
Holcik J. (ed.), 1989. The freshwater fishes of Europe. Wiesbaden: AULA Verl., Vol. 1. P.2. 469 p.
Khodorevskaya, R.P., E.V. Krassikov, G.F. Dovgopol and O.L. Zhuravleva, 1997. Ickthyological monitoring of the sturgeon stock status in the Caspian Sea. In: Biodiversity monitoring. Moscow. 159-164.
Krasikov, E.V. and A.A. Fedin, 1996. Distribution and trends of sturgeon abundance in the Caspian Sea based on the results of 1991-1995 investigations. In: State and prospects of scientific- practical developments in the field of Russian mariculture . VNIRO Press. Moscow. P.p. 138-142.
Legeza, M.I. 1972. Role of abiotic environmental factors in the distribution of sturgeons (the family Acipenseridae, Pisces) in the Caspian Sea. Voprosy Ikhtyologii (Problems of Ichthyology). Vol. 12, 1: 13-24.
Miller, R. 1969. Quaternary freshwater fishes of North America. The quaternary period in the USA. Mir (Peace) Press Moscow. Vol. LV, 4: 371-374.
Mussaev, P.G. 1972. The status of the spawning population of Russian sturgeon in the Terek River in 1971. Abstracts of TSNIORKH Reporting Session. Astrakhan. P.p. 104-105.
Pavlov, A.V. and G.A. Yelizarov, 1967. Results of sturgeon tagging in the Volga-Caspian region during 1958-1965. Abstracts of TSNIORKH Research Session. Baku. P.p. 62-64.
Pavlov, A.V. and S.S. Zakharov, 1971. Distribution, quantitative composition and abundance of sturgeons in the Northern Caspian in 1967. TSNIORKH Proceedings. Baku. P.p. 62-64.
Peseridi, N.E. 1986. Fish of Kazakhstan. Nauka Press. Alma-Ata. P.p. 57-162.
Slivka, A.P., G.F. Zykova, E.V. Krassikov, V.A. Fedorov, V.V. Shvedov and V.A. Chukanov, 2000. Qualitative structure, abundance trends, distribution and the state of sturgeon stocks in the Caspian Sea in 1999. In: Fisheries studies in the Caspian Sea: results of research work in 1999. CaspNIRKH. Astrakhan. P.p. 154-160.
Stygar, V.M. 1984. Feeding and nutritional relations between young sturgeons and other fish in the lower reaches of the Ural River. Author's Abstract of the Ph.D. Dissertation. VNIRO Press. Moscow. 24 p.
Vlasenko, A.D. Biological principles of sturgeon reproductions in the regulated Volga and Kuban. Author's Abstract of the Dissertation for Ph. D. VNIRO Press. Moscow. 25 p.
Zhuravleva, O.L. 2000. Dynamics of biological characteristics of the Russian sturgeon (Acipenser gueldenstaedtii Brant) spawning population in the Volga River under conditions of regulated river flow. Author's Abstract of the Dissertation for Ph. D. VNIRO Press. Moscow. 28 p.

Compiled by:

O.L. Zhuravleva, CaspNIRKH, Astrakhan, Russia
Yu.A. Kim, AfKazNIRKH, Kazakhstan
Z.M. Kuliev, AzerNIRKH, Azerbaijan

Acknowledgements:

to E.V. Krasikov, for his important comments;
V.A. Fedorov, N.V. Shabanova - for preparing maps