Taxonomic description of species
Body torpedo-like. Snout conic. Gill membranes attached to isthmus. Mouth inferior, transverse, protractile, exceeds half of snout width. Characteristic features: large first dorsal scute, "uninterrupted" lower lip, and fringed barbels. No bony shields between rows of scutes. Color: body brownish, similar to sterlet, different from other sturgeons; white belly, light scutes. Scutes large, arranged in five rows; dorsal 11-16, 51-74 lateral, and 11-17 ventral. D 39-54, A 24-34, gill rakers 30-45.
Intraspecific forms: A.nudiventris derjavini Borsenko, 1950; A.nudiventris aralensis
Related forms: Acipenser gueldenstaedtii Brandt, 1833; Acipenser persicus Borodin, 1897;
Acipenser baeri Brandt, 1868; Acipenser stellatus Pallas, 1771; Acipenser ruthenus Linnaeus, 1758
Distribution of species within the Caspian Sea
Acipenser nudiventris is unevenly distributed in the Caspian Sea; it is rather abundant in the South Caspian (primarily southward the Kura River), enters the Kura and Sefidrud Rivers (Borzenko, 1961; Abdurakhmanov, 1962).
Status as per International Red Data Book: EN.
Status as per National Red Data Books: Russia - EN, Kazakhstan - EN, Azerbaijan - EN, Turkmenistan - EN, Iran - EN.
First record for the Caspian Sea: Kessler, 1856.
Redescription of species: Berg, 1911.
General characteristics of species
Ecological-taxonomic group. Nekton
Origin. Ponto-Caspian endemic
World distribution. The Caspian and Aral Seas; occurs rarely in the Black and Azov Seas (Berg, 1948).
Habitat. Bottom fish, prefers shallow areas of the shelf with sand, sand/ silt bottoms. It occurs at depths 11-25 m, water temperature
2.7-14.60C.
Migrations. Anadromous spawning, post-spawning downstream and feeding migrations.
The species migrates along the Kazakhstan coast of the Middle Caspian, from the Tyub-Karagan Peninsular - northward along the eastern steep slope of Ural Deep Trench towards Peschany Island. Spawning migrations - to the Kura, Ural, Sefidrud Rivers.
Relation to abiotic environmental factors
Relation to salinity. Brackishwater euryhaline species capable of prolonged stay in fresh water.
Relation to temperature. Eurythermic species.
Vertical distribution. Stenobathic species (10-50 m).
Relation to oxygen conditions. Oxyphilic species; oxygen content under 60% is disastrous.
Relation to fluctuations of the sea level. Sea level fluctuations affect the species through changes in food supply.
Feeding
Feeding type. Heterotrophic, holozoic.
Feeding behavior. Active predator.
Food spectrum. Euryphagous species.
Food supply. The Ural and Kura ship sturgeon do not feed during spawning and wintering periods (including related migrations). Adults in the sea feed mostly on fish: up to 90% of the diet consists of gobiids, kilka, sandsmelt. Their diet includes crustaceans -
Gammaridae, Cumacea, Mysidae, Nereis as well as crab, shrimp and mollusks (Derzhavin, 1949; Borzenko, 1950; Zheltenkova, 1964). Juveniles feed on zoobenthos
Quantitative characteristics of feeding. The qualitative dietary composition of young ship hardly changes in different years, while its quantities vary considerably. In certain years, diets of fingerlings (up to 70 mm TL) was composed of Gammaridae - 38-69% in weight, Corophiidae - 22-30 %, Trichoptera larvae - 12-13%, larval Chironomidae - up to 13%. Average index of stomach fullness varied from 66.9 to 246 0/000, that of the whole digestive tract - from 224 to
4110/000. Individuals with empty stomachs amounted to less than 2% (Stygar, 1981). Index of stomach fullness in fish captured at the western coast of the Middle and South Caspian ranged within
33.2-89.70/000 (juveniles) and 24.8-231.00/000 (adults).
Reproduction
Reproduction type. Gamogenesis.
Reproduction areas. Spawning sites for ship sturgeon in the Kura River are located 600 km upstream the mouth (Derzhavin, 1956; Borzenko, 1950, 1961); in the Ural River - 350-650 km from the mouth. The spawning substrate: pebble, sandstone, coarse sand, thick clay with shell incorporation
Terms of reproduction. Spawners run into the Kura River throughout the year, two peaks are observed: the main - in March-April, the secondary - in
October-December. Reproduction takes place in May-June at water temperature
15-250C. Acipenser nudiventris entering the Ural River is represented mostly by the vernal race, hiemal specimens occur sporadically (Pesseridi, 1964, 1966, 1972).
Spawning temperature in the Ural River is within 12-180C. Spawning interval -2-3 years.
Dynamics of ship spawning migration into the Kura River, %
| Year |
Month |
n |
| I |
II |
III |
IV |
V |
VI |
VII |
VIII |
IX |
X |
XI |
XII |
| 1983 |
5.4 |
3.3 |
16.3 |
25.1 |
6.5 |
- |
- |
- |
1.1 |
13.0 |
20.6 |
8.7 |
92 |
| 1984 |
4.5 |
3.0 |
3.0 |
4.5 |
1.5 |
1.5 |
- |
12.2 |
4.5 |
19.8 |
28.8 |
16.7 |
66 |
| 1985 |
- |
1.3 |
16.6 |
2.6 |
1.3 |
- |
- |
1.3 |
9.1 |
32.4 |
22.1 |
14.3 |
77 |
| 1986 |
2.3 |
4.6 |
3.4 |
21.8 |
3.4 |
- |
- |
1.1 |
2.3 |
8.1 |
32.3 |
20.7 |
87 |
| 1987 |
9.1 |
5.6 |
28.4 |
12.5 |
1.2 |
- |
- |
- |
1.2 |
42.0 |
- |
- |
88 |
Fecundity. The mean fecundity of ship sturgeon in the Kura River is 594,000 (280,000-1,003,000) eggs; in the Ural River it varied in recent years from 386,500 (1999) to 561,500 (1996) eggs.
Qualitative characteristics of ship sturgeon population in the Ural River
|
Year |
Length,
cm |
Weight,
kg |
Fulton Condition Factor |
Proportion of females in catches, % |
Absolute fecundity,
thousand eggs |
| 1996 |
148.8 |
24.3 |
N/A |
37.4 |
561.5 |
| 1997 |
148.5 |
19.3 |
0.57 |
38.5 |
417.9 |
| 1998 |
151.8 |
23.1 |
0.79 |
48.9 |
465.0 |
| 1999 |
148.4 |
20.5 |
0.61 |
41.8 |
386.5 |
| 2000 |
141.6 |
16.4 |
0.59 |
28.4 |
397.2 |
Limiting factors:
- Abiotic:
The Kura River: temperature conditions, water discharges; the Ural River: flood volume, winter oxygen deficits in the lower reaches.
- Biotic:
Predation on eggs (gudgeon, gobies, silver bream, bream, catfish) and fingerlings (catfish and zander) during the riverine period.
- Anthropogenic:
Reduced number of spawners as a result of illegal harvest; pollution of rivers, damming of the Kura River (loss of spawning areas).
Life history and development
Life history stages
- Embryonic development.
- Prelarvae - until transition to active feeding.
- Larvae - appear in the lower reaches of the Ural River during the third or fourth five-day period of May.
- Fry - the peak of their downstream migration in the Ural River is recorded from late May to mid-July.
- Juveniles - until maturation
Large number of young fish winters in the river. Some of them migrate into the sea in the following year. Those who undertake second wintering in the river transform into the riverine/ freshwater form and remain there forever.
Relation to environmental factors. The annual number of young ship sturgeon migrating downstream the Ural River varies depending on flood volume: mean catches per tow in years with large water discharges are far bigger as compared with low-water years. Ship sturgeon juveniles in the river are eaten away by catfish and zander. Their survival is less than that of other sturgeons because of prolonged riverine period
Age of maturity. Ship sturgeon males in the Kura River mature at the age of 9 years old, females - usually at 14 years, seldom at 12-13 years. Ship sturgeon males in the Ural River reach maturity at the age of 6-9 years (most males at 9-13 years), females - at 8-10 years (mostly at 13-16 years).
Thermal conditions of development. Embryonic development in the Kura River takes place at water temperature
19.5-21.90C.
Quantitative characteristics of growth. Ship sturgeon in the Ural River shows the highest growth rate as compared with Balkhash and Aral ship sturgeons.
Structural and functional population characteristics
Sex ratio. Sex ratio of ship sturgeon in the Kura River population is variable, nevertheless males always predominate (3-6 times) over females. The proportion of females in the Ural River population decreased from 48.9% (1998) to 28.4% (2000).
Age-size structure. Mature specimens in the Kura River vary in length: 111-221 cm (females), 97-205 cm (males); in weight: 11.7-40 kg, mean Wt - 24.3 kg in females, 18.1 kg in males. Mature ship sturgeon in the Ural River has 97-221 cm TL, more frequently 130-180 cm. The mean length of females is 172 cm, 144 cm in females.
Length and weight characteristics of ship sturgeon taken from catches in the Ural River, 1961-1969
(cited: "Fish of Kazakhstan", 1986)
| Age, years |
Males |
Females |
Both sexes |
| cm |
kg |
n |
cm |
kg |
n |
cm |
kg |
n |
| 7 |
102 |
6.5 |
2 |
- |
- |
- |
102 |
6.5 |
2 |
| 8 |
108 |
8.2 |
4 |
- |
- |
- |
108 |
8.2 |
4 |
| 9 |
120 |
11.4 |
25 |
- |
- |
- |
120 |
11.4 |
25 |
| 10 |
127 |
12.2 |
39 |
- |
- |
- |
127 |
12.2 |
39 |
| 11 |
131 |
13.6 |
36 |
147 |
22.0 |
10 |
135 |
15.4 |
46 |
| 12 |
134 |
14.5 |
51 |
151 |
23.4 |
17 |
138 |
16.7 |
68 |
| 13 |
137 |
15.7 |
63 |
154 |
23.8 |
16 |
140 |
17.3 |
79 |
| 14 |
140 |
17.9 |
67 |
160 |
24.9 |
24 |
145 |
19.7 |
91 |
| 15 |
146 |
19.3 |
78 |
161 |
25.6 |
54 |
152 |
21.9 |
132 |
| 16 |
150 |
20.1 |
74 |
164 |
27.3 |
103 |
158 |
24.3 |
177 |
| 17 |
157 |
22.2 |
59 |
166 |
28.6 |
129 |
163 |
26.6 |
188 |
| 18 |
162 |
23.6 |
56 |
170 |
29.7 |
83 |
167 |
27.3 |
139 |
| 19 |
165 |
24.1 |
39 |
174 |
30.9 |
67 |
177 |
28.4 |
106 |
| 20 |
167 |
24.8 |
23 |
177 |
31.4 |
43 |
174 |
29.1 |
66 |
| 21 |
170 |
25.2 |
17 |
181 |
32.8 |
25 |
177 |
29.7 |
42 |
| 22 |
172 |
26.9 |
12 |
184 |
33.6 |
23 |
180 |
31.3 |
35 |
| 23 |
174 |
27.4 |
14 |
186 |
34.4 |
19 |
181 |
31.4 |
33 |
| 24 |
177 |
28.1 |
15 |
189 |
34.7 |
11 |
183 |
30.9 |
26 |
| 25 |
180 |
29.3 |
13 |
191 |
37.1 |
16 |
186 |
33.6 |
29 |
| 26 |
178 |
30.2 |
9 |
193 |
37.7 |
9 |
186 |
34.0 |
18 |
| 27 |
181 |
32.8 |
9 |
194 |
39.2 |
10 |
188 |
36.2 |
18 |
| 28 |
180 |
33.9 |
8 |
187 |
41.8 |
6 |
187 |
37.3 |
12 |
| 29 |
184 |
38.4 |
3 |
204 |
43.4 |
5 |
196 |
41.5 |
8 |
| 30 |
- |
- |
- |
200 |
41.6 |
6 |
200 |
41.6 |
9 |
| 31 |
- |
- |
- |
206 |
39.7 |
4 |
206 |
39.7 |
4 |
| 32 |
- |
- |
- |
204 |
44,3 |
3 |
204 |
44.3 |
3 |
| 33 |
- |
- |
- |
198 |
40.0 |
1 |
198 |
40.0 |
1 |
| Average |
147.9 |
19.78 |
716 |
173.1 |
29.9 |
684 |
160.1 |
24.7 |
1400 |
The mean age of the Ural River population is 9-13 years. The maximum recorded age reached 33 years during 1961-1963, in 2000 - 21 year.
Quantitative characteristics. In 1980-s, the annual number of spawners in the Kura River varied from 66 to 112 individuals; only single specimens of
Ac. nudiventris were registered in 1998-2000. In 2000, the abundance and biomass of the spawning stock in the Ural River amounted to 6,280 individuals and 24 tons, respectively.
Dynamics of quantitative characteristics of ship sturgeon stock in the Ural River
(Kim, Bokova, 1991-2000)
| Years |
Annual runoff in the Ural River,
km3 |
Total abundance of spawning population, thou.
ind. |
Catches |
Number of spawners accessed spawning grounds, thou.
ind. |
Number of fingerlings migrated downstream, million
ind. |
| thou. ind. |
thou. t |
| 1991 |
10.6 |
13.6 |
0.5 |
0.014 |
13.1 |
0.97 |
| 1992 |
6.0 |
15.1 |
7.6 |
0.20 |
6.3 |
0.016 |
| 1993 |
15.0 |
8.06 |
2.96 |
0.06 |
5.1 |
4.5 |
| 1994 |
15.4 |
2.7 |
1.2 |
0.03 |
1.5 |
0.39 |
| 1995* |
6.0 |
- |
- |
0.02 |
- |
- |
| 1996 |
3.8 |
5.6 |
1.3 |
0.03 |
3.0 |
0.563 |
| 1997 |
5.7 |
5.6 |
1.4 |
0.03 |
2.3 |
0.363 |
| 1998 |
12.0 |
4.4 |
2.8 |
0.06 |
2.4 |
1.3 |
| 1999 |
5.0 |
6.55 |
1.598 |
0.03 |
3.3 |
- |
| 2000 |
11.0 |
6.28 |
1.268 |
0.024 |
2.6 |
2.0 |
* Studies were not conducted in 1995
Population trends. Ship abundance in the Kura River decreases steadily. Its stock in the Ural River is also in decline, though a slight increase was recorded in 1999-2000, as compared to the period of 1996-1998.
Interspecific relations
Food competitors of young ship sturgeon are gudgeon, white-eyed bream, silver bream, roach as well as fingerlings of young common carp, bream, great sturgeon and Russian sturgeon. Adults compete with beluga and, partly, with zander, kutum and asp for food. During the riverine period of their life history, large numbers of ship fingerlings are consumed by catfish and zander.
Importance of species to bioresources production of the Caspian Sea
Economic significance of species. Valuable commercial fish species.
Commercial characteristics of species, catches. Ship sturgeon catches in the Kura River decreased gradually after dams construction.. In recent years it occurred sporadically.
By mid-1970-s, the abundance of ship sturgeon in the Ural River increased considerably
due to the ban on its commercial harvest introduced in 1964 (effective until early 1990-s). In 1990-s, the catches reached 2000 tons (1992). By the late 1990-s, the trend to their reduction persisted, so that only 24 tons were harvested in 2000.
Fishing gears and fishing zones. Riverine beach seines were used at stationary fishing sites of the Ural River, fixed nets - in the Ural estuary.
Impact of fisheries on the population status
The impact is assessed as negative; unsustainable fishery leads to the decline in the Ural ship sturgeon population. The harvest should take 40% of the population at most.
Human impact/Threats. Overfishing, enormously increased poaching, pollution of the Ural River and the Caspian Sea determine the drop of the Ural ship sturgeon population.
The main causes of the drastic decline in ship sturgeon catches in the Kura River are as follows:
- the Kura River damming (1953) and loss of spawning areas, consumptive water use/ low river runoff;
- sturgeon fishing at sea (until 1962);
- damage caused by marine seismic prospecting (in 1970-s);
- sea pollution and subsequent loss of sturgeon feeding areas (e.g., the feeding ground around Sumgait, shallow areas from Apsheron to the Kura River mouth, etc.);
- illegal fishing/ poaching.
Conservation measures:
- Maintenance of natural reproduction, fisheries (targeted) reclamation of sturgeon spawning grounds. Enhance access of spawners into the Ural river (up to 60% of the population number). Improve hydrological conditions at the Kura river for the purposes of natural reproduction.
- Poaching control in the Ural and Kura Rivers.
- Ban on the commercial fishery of ship sturgeon in the Kura River, Ural estuary, and the Caspian Sea. Ship sturgeon should be harvested only for fisheries purposes.
- Increase in restocking rate of ship sturgeon population/ hatchery production at the Kura River - up to 2 million juveniles annually.
References
Abdurakhmanov, Yu.A. 1962. Freshwater fish of Azerbaijan. Az.SSR AS. Baku. P.p. 34-43.
Berg, L.S. 1911. Fauna of Russia. Fish. St.-Petersburg. Vol. 1. 250 p. (in Russian)
Berg, L.S. 1949. Freshwater fish of the USSR and adjacent states. USSR AS. Part 2. Moscow-Leningrad. 458 p. (in Russian).
Borzenko, M.P. 1950. Materials on systematic, biology and fishery of the Kura ship sturgeon. Proceedings of the Caspian Branch of VNIRO. Vol. 11. Astrakhan. Pp. 9-48. (in Russian).
Borzenko, M.P. 1961. Present status of stocks and fishery of sturgeons in Azerbaijan and methods for its rationalization. Moscow. 37 p. (in Russian).
Bekeshev, A.B. and N.E. Pesseridi, 1966. Downstream migration of young sturgeons in the Ural River. In: Biological principles of the fisheries in water bodies of Middle Asia and Kazakhstan. Alma-Ata. Pp. 49-51.
Caspian Sea. Ichthyofauna and commercial resources. 1989. Nauka Press. Moscow. Pp. 27-41 (in Russian).
Derzhavin, A.N. 1947. Sturgeon stock reproduction. Baku. 243 p. (in Russian).
Derzhavin, A.N. 1956. Animal Kingdom of Azerbaijan. Kura fisheries. AzSSR AS. Baku. 435 p. (in Russian).
Fish of Kazakhstan, 1986. Vol.1. Nauka Press of KazSSR. Alma-Ata. Pp.139-156.
Kessler, K.F. 1877. Fish inhabiting and occurring in the Aral-Caspian-Pontic ichthyological region. In: Proceedings of the Analo-Caspian Expedition, 4. St.-Petersburg. Pp. 1-360. (in Russian).
Legeza, M.I. 1973. Present distribution of sturgeons (the family Acipenseridae) in the Caspian Sea. J. Voprosy Ikhtyologii (Problems of Ichthyology). Vol. 13, 6(83): 1008-1015 (in Russian).
Makarova, I.A., A.P. Alekperov, and T.S. Zarbalieva, 1991. Present status of the spawning population of the Kura ship sturgeon and methods for its conservation. J. Voprosy Ikhtyologii (Problems of Ichthyology). Vol. 31: 148-153 (in Russian).
Ovsepyan, G.P., N.E. Pesseridi, 1976. Results of observations on the dynamics of ship sturgeon run and composition of its spawning population in the Ural River (1971-1974). Book of Abstract of TSNIORKH Report Session according to the results of activities during the 9th five-year period. Guriev. Pp. 30-31. (in Russian).
Pesseridi, N.E. 1996. Some data on sturgeon reproduction and utilization of spawning sites in the Ural River. In: Biological principles of the fisheries in water bodies of Middle Asia and Kazakhstan. Alma-Ata. Pp. 46-48.
Pesseridi, N.E. 1971. Seasonal dynamics of sturgeon run in lower reaches of the Ural River. In: USSR sturgeons and their reproduction. TSNIORKH Proceedings. Vol. 3. Moscow. Pp. 355-358. (in Russian).
Pesseridi, N.E. 1972a. Importance of the Ural River for Caspian fish reproduction. In: Biological resources of the Caspian Sea. Pp. 118-121. (in Russian).
Zheltenkova, M.V. 1964. Sturgeon feeding in southern seas. VNIRO Proceedings, Vol. 54 pp. 9-48. Moscow (in Russian).
Zakharyan, G.B. 1972. Materials on natural conditions for sturgeon reproduction in the Kura River. In: USSR sturgeons and their reproduction. TSNIORKH Proceedings. Vol. 4. Moscow. Pp. 67-77. (in Russian).
Compiled by:
Yu.A.Kim (KazNIIRKh Atyrau Branch, Atyrau, Kazakhstan)
Z.M. Kuliev (AzerNIRKh, Baku, Azerbaijan)
T.O. Zarbalieva (AzerNIRKh, Baku, Azerbaijan)
I.M.Aminova (KazNIIRKh Atyrau Branch, Atyrau, Kazakhstan)