Acipenser persicus, Borodin, 1897

Taxonomic description of species

Unlike Russian sturgeon, body more elongate and bulky, bluish in shade, head longer -17.6% of body length (TL), snout and postorbital distance increased. Corresponding differentiation rates (t) are 4.51, 4.17, and 4.25, respectively. Head depth at nape - 8.61% of TL. Maximum body depth in females - 17.44%, in males - 16.27% of TL. Ventral scutes/plates 6-12, D 31-50 (39.0 in average), A 16-30 (24.8 in average) (Putilina, 1983)
Intraspecific forms. Persian sturgeon from the Caspian rivers, Kura and Ural, is homogeneous as regards the main meristic and plastic features (Peseridi, 1986). Existence of winter race was assumed based on different functional status/ maturity stages of spawners entering the Volga river (Putilina, Artyukhin, 1985).
Related forms. Other sturgeon species within genus Acipenser.

Distribution of species within the Caspian

Persian sturgeon feeds at the shelf zone of the sea, primarily in the eastern part of the South Caspian. Individual specimens are found in the North Caspian, western part of the Middle and South Caspian (along Lenkoran shores) (Kuznetsova, Palgui, 1992) .
Status as per International Red Data Book. EN
Status as per National Red Data Books. Russia - VU; Azerbaijan - VU; Kazakhstan - VU; Turkmenistan - N/A; Iran - VU.
First record for the Caspian. Kessler, 1877.
Redescription of species: Borodin, 1897; Kavraisky, 1907; Berg, 1911; Derzhavin, 1939; Borzenko, 1961; Legeza, 1970; Lukyanenko et al., 1974; Artyukhin, 1979
Putilina, 1983.

General characteristics of species

Ecologo-taxonomic group. Nekton
Origin. Ponto-Caspian endemic species
World distribution. Caspian and Black seas and rivers entering into them.
Habitat. Bottom dweller save for the spawning migration, when fish traverse through water column. Occurs primarily at mud and/or sand bottoms (Legeza, 1972).
Migrations. Undertakes feeding, spawning and post-spawning migrations. Enters the rivers for spawning, mainly Kura river, less - the Volga, Ural, rivers of Dagestan (Samur, Terek) and Azerbaijan (Lenkoranka, Astara), and Sefid-Rud.

Relation to abiotic environmental factors

Relation to salinity. Euryhaline species. The majority occurs in typical marine Caspian waters (Legeza, 1972).
Relation to temperature. Eurythermic species. Occurs at sea water temperature ranged 4.10 - 28.0⁰C, in summer - 12.0-23.5⁰C, in winter - 12.0-14.0⁰C, in spring - 10.0-12.0⁰C (Legeza, 1972). Spawners enter the Volga river at 4-5⁰C, the Ural river - at 5-6⁰C.
Vertical distribution. Euribathic species, resides at continental terrace above 100-m depth, makes regular seasonal movements; in winter occurs at the depth 20-40 m, in summer - 10-20 m.
Relation to oxygen conditions. Oxyphilic species, occurs at oxygen concentrations 71.7 - 105.5%.

Feeding

Feeding type. Heterotrophic
Feeding behavior. Detects food item with tactile and gustatory receptors, then makes sucking movements with protractile oral apparatus.
Food spectrum. In Kura river migratory fingerlings (16-73 mm TL) feed on Mysidae, Chironomidae and Gammaridae (total index of stomach fullness - 195-1,000 ⁰/₀₀₀). In the south-eastern part of the Caspian juveniles aged 2-3 years consumed crabs and fish. In the course of growth importance of dietary fish increases up to 70-80%. Persian sturgeon sized up to 81-120 cm fed primarily on fish (53.4%).
Quantitative characteristics of feeding. Circadian feeding activities: Persian sturgeon feeds more actively at diurnal and nocturnal hours. Seasonal changes in diet are characteristic of this species: in spring, the main food items were Gammaridae and fish; in summer - Gammaridae and Cumacea. Indices of stomach fullness in juveniles were higher in spring (57.5 ⁰/₀₀₀, 32.0% of sampled fish with empty stomachs), than in summer (10.0 ⁰/₀₀₀ and 50.0%, respectively)(Zarbalieva, 1973).

Reproduction

Reproduction type. Sexual
Reproduction areas. In the Volga river reproduces at channel sites (flow speed 1.2-1.6 m*sec^-1, water temperature 20-25⁰C) of the middle and lower spawning areas (Khoroshko, 1970). In Kura river spawning grounds are located at the dam area of Varvarinsky reservoir; in Araks - 10 km below Bagramtapinskaya dam. Before regulation of Kura and Araks streams, the main spawning grounds were located in the mid-flow Kura river, at Mingechaur - 660 km from the mouth, in the river Araks - 330 km away at Karadonly. Spawning in Ural river occurs at the areas 1,000 km upward the mouth, in terms coincident with those of the Russian sturgeon (Peseridi, 1986).
Terms of reproduction. Spawning in the Volga river occurs in the end of July - first 10 days of August (Lagunova, 2001), the majority of fish spawns at water temperature 20-22⁰C. In Kura spawning occurs between second half of April - mid-September, with peak in August; in Ural river - in June-July.
Different physiological status of spawners entering the Volga river enabled to conclude on the existence of hiemal race of Persian sturgeon (Putilina, Artyukhin, 1985).
Fecundity. In the Volga river fecundity of Persian sturgeon varied from 310*10³ to 390*10³ eggs, as estimated for the period 1991-2000. Decrease of fecundity values (down to 310*10³ in 2000) is related to decrease of females of senior age groups. Fecundity in populations from Kura and Ural averages 320*10³ eggs (Artyukhin, 1979).

Characteristics of Persian sturgeon spawners in the Volga river
(fishing site "Chkalovskaya")

Limiting factors. Reproduction efficiency depends on hydrological conditions at the river, primarily, water temperature. Spawning in Kura suspends from mid-summer to September due to high water temperatures. In 1980-s, number of spawners to be accessed to the spawning grounds added to the list of limiting factors.

Life history and development

Life history stages. In the course of development follows the same stages characteristic of all sturgeon species, i.e.: embryo, prelarva, larva, fingerling, juvenile and adult (Detlaf et al., 1981). Duration of embryonic period (2-10 days) is the same as for Russian sturgeon; these species could not be distinguished at embryonic and early larval stages. Larvae transit to active feeding at 17-17 mm TL, 9 days after hatching.
Age of maturity. Males from the Volga river population mature at the age of 9 years, females - at the age of 12 years. In Kura river population males mature at the age of 7-8 years, females - 10-11 years. The Ural river population has respective characteristics 7-8 years and 9-10 years. Spawning interval for females - 3-6 years, more often 4-5 years.
Quantitative characteristics of growth. The Persian sturgeon in Kura river shows moderate weight gain during the first years of life, which increases considerably in 8-year-old fish. In succeeding years, the build-up of weight goes more slowly. To the contrary, linear growth is particularly rapid during the first two years and later decreases abruptly. The population from the river Ural ranks below the Kura population as regards growth rate.

Structural and functional population characteristics

Sexual structure. Decrease of females abundance persists currently; in 1999-2000, proportion of females in the Volga river was equal to 17.0%, males - 83%. In the Ural and Kura rivers females/males ratio was approximately equal to 1:1
Age-size structure. The majority of males in the Ural river is represented by fish aged 10-21 years (84.7%), modal age group is 12-17 years (54%). Males aged over 21 year are scanty. Females are mostly 15-24 years old (76.4%). The main part of the population is represented by specimens aged 7-20 years (42.5%). In the Volga river age structure is ranged from 14 to 36 years, 74.2% constitute fish aged 20-26 years. The mean female age is 24.4 years, mean age of male is 23.4 years (Putilina, 1983).

Age structure of Persian sturgeon population in the Volga river (1996-2000)

In 1991-2000, linear characteristics of migratory spawners in the Volga river delta ranged within 68.0-107.0 cm, weight - within 4.7-13.2 kg, age - within 4-12 years. Males aged 7-30 years, in average 12-17 years, enter the Kura river, age of females - from 13 to 34 years; more frequently fish are 19-24 years old. Persian sturgeon caught at sea ranged from 3 to 33 years, maximum (60.5%) was due to fish aged 7-14 years. In 1983, size characteristics of Persian sturgeon in the Volga river varied from 109 to 200 cm. The mean body length was 169.9 cm in females, 162.1 cm in males. In 2000, corresponding values were 152.2 cm and 134.1 cm. In 1999-2000, body length of Persian sturgeon varied between 105-242 cm in females, 86-226 cm in males. Up to 75% fish in catches comprised specimens of 160-170 cm TL.
Quantitative characteristics. In 1989-1991, relative abundance ranged from 0.88 to 0.49 specimens per trawl (Kuznetsova, Palgui, 1992).

Interspecific relations

Competitive relations with sevruga/ stellate sturgeon, Russian sturgeon, and gobiids may arise at the feeding grounds in the Caspian Sea.

Importance of species to bioresources of the Caspian Sea

Economic significance of species. Important commercial fish.
Commercial characteristics of species, catches. The biggest catch in Azerbaijani waters was registered in 1936 - 1540 tons. By the beginning of 1950-s, the catches dropped to 630 tons, by 1960-s - to 310 tons. The catches in Iranian waters corresponded to 250 tons in early 1950-s, reached 920 tons in early 1960-s. The catches in the Volga and Ural rivers were not recorded due to insignificant proportion of the species in total catches. In the Volga river the share of Persian sturgeon ranged from 0.4 to 0.03% in 1991-2000.

Persian sturgeon percentage in the total number of migratory sturgeons,
long-term sampling at the fishing site "Chkalovskaya", the Volga river

Fishing gears and fishing zones. Prior to 1865, the main fishing gears used at the Caspian were stems and beach seines. Afterwards, hook gears and different nets - floating, stationary, etc., were employed. Since 1962, fishing (with beach seines) was transferred to the rivers, except for Iran. Since 2001, Persian sturgeon of the Volga river is used only for reproduction purposes.

Impact of fisheries on the population status

The catches of the Persian sturgeon decline drastically. While in 1980-s they composed 4.0% of the total sturgeon catches from the Volga river, in the year of 2000 the share of this species decreased to 0.03%. At the Ural river it did not exceed 5%. Fishing at sea leads to extraction of immature fish, thus the spawning population decreases, consequently, natural reproduction and stocks fall.
Human impact/Threats. The major factors, which contribute to decline of population number in the Persian sturgeon, are:

• stream regulation/ damming at the rivers,
• loss of spawning areas,
• permanently increasing contamination of the rivers and the Caspian Sea,
• fishing at sea.

Conservation measures. In order to restore Persian sturgeon stocks, measures should be undertaken to increase artificial reproduction of this species at hatcheries.

References

Artyukhin E.N. 1979. Persian sturgeon in the rivers of the North Caspian and prospects of its exploitation in sturgeon economy. In: " Biological bases for development of sturgeon economy in water bodies of USSR. P. 105-114.
Berg L.S. 1911. Fauna of Russia. Fishes. St. Petersburg. 1: 246-251.
Borodin N.A. 1887. Materials on sturgeon biology. Proc. Dept. Ichthyology, Academy of Sciences. 2: 261-272.
Detlaf T.A., A.S. Ginsburg and O.I. Shmal'gauzen. 1981. Development of sturgeon fishes. Nauka publishers, Moscow. 224 p.
Kavraisky F.F. 1907 .Sturgeons of the Caucasus. Caucasian Museum Publ. 16 p.
Kessler K.F. 1877. Fishes inhabiting and occurring in the Aral-Caspian region. Proc. Exp. St. Petersburg. IV: 360 p.
Khoroshko P.N. 1970. Ecology of spawning in the changed Volga river. Proc. TsNIORKh (Central Sturgeon Research Institute). 2: 105-111.
Kuznetsova N.S. and V.A. Pal'gui. 1992. Persian sturgeon: distribution and structure based on materials for years 1989-1991. In: "Biological resources of the Caspian Sea". Abstr. Ist Intern. Conf. Astrakhan. P. 204-206.
Lagunova V.S. 2001. Natural reproduction of the Persian sturgeon (Acipenser persicus) in the lower Volga river. In: "Problems of research and sustainable use of marine natural resources". Astrakhan. P.118-124.
Legeza M.I. 1972. Role of abiotic environmental factors in distribution of sturgeons (Fam. Acipenseridae, Pisces) in the Caspian Sea. "Vopr. Ichthyol. (Problems of Ichthyology)". 121, 1: 13-24.
Legeza M.I. 1975. Caspian sturgeon stocks and their exploitation under current conditions. Proc. VNIRO. VIII: 121-134.
Lukyanenko V.I., J.G. Umerova, and B.B. Karataeva. 1974. South-Caspian sturgeon - separate species of the genus Acipenser. Proc. USSR Acad. Sci. 5: 458-461.
13. Peseridi N.E. 1986. Fishes of Kazakhstan. Alma-Ata. Nauka publishers Kazakhstan SFR. P.99-109.
Putilina L.A. 1985. Quantitative and qualitative assessment of spawning population of Persian sturgeon in the Volga river. "Rybnoe khozyaistvo (Fishing industry)". 10: 71-72.
Putilina L.A. and E.N. Artyukhin. 1985. Some features of Persian sturgeon migration in the lower Volga river. Ibid. P. 32-34.
Zarbalieva T.S. 1973. Age-related and seasonal changes in feeding sturgeon juveniles at the western coast of the Middle Caspian. In: "Advance in Azerbaijan fisheries research". Baku. P. 63-81.
Zarbalieva T.S. and T.I. Detkina. 1981. Characteristics of sturgeon feeding habits in different regions of the Caspian Sea. In: "Rational bases for running sturgeon economy." Abst. Appl.-Res. Conf. P.83-84. Volgograd. P. 84-85.

Compiled by:

Z.M. Kuliev (AzerNIRKh, Baku, Azerbaijan),
L.A. Ivanova (CaspNIRKh, Astrakhan, Russia)