Taxonomic description of subspecies
Body length: 22-46 cm, mean TL - 35 cm, weight: 150-1,400 g, mean wt - 550 g. Gill-rakers on first gill arch 51-96, 74.6 in average. Vertebrae 49-54, more often 51-53, 51.8 in average. Teeth well developed. Jaws of equal length, otherwise lower jaw slightly extended. Head comparatively short, depth moderate, head length 20-26% (mean 22.8%) of TL;
head depth 13-18% (mean 16.4%) of TL. Eye relatively small, 13-23% (mean 19.5 %) of head length. Body deep, at its maximum 20-28% (mean 23.8%) of TL, at minimum 6-8% (mean 7.0 %) of TL. Color: body darkish, dorsally dark violet, pectorals dark on top. Usually dark spot posterior of opercle.
Intraspecific forms: Alosa kessleri kessleri (Grimm, 1887); Alosa kessleri volgensis
(Berg, 1913)
Related forms: Alosa kessleri pontica (Eichwald, 1838), the Black Sea
Distribution of subspecies within the Caspian Sea
The subspecies occurs rarely ar sea. Main concentrations are observed in the southern part of the Caspian. Enters the Volga River for spawning (up to the dam of the Volgograd HEPS/ Hydroelectric Power Station).
Status as per International Red Data Book: N/A.
Status as per National Red Data Book. N/A.
First record for the Caspian Sea: Pallas, 1771
Redescription of subspecies: Kessler, 1870; Grimm, 1887; Berg, 1913; Svetovidov, 1943
General characteristics of subspecies
Ecologo-taxonomic group. Nekton
Origin. Autochthonous Caspian species
World distribution. Caspian Sea endemic
Habitat. Pelagic zone
Migrations. Spawning - anadromous run of spawners from the southern parts of the Caspian sea
into the Volga River at a distance of about 2,000 km;
Wintering - the run of fish to the southern parts of the Caspian, the zones with the optimum
parameters of water temperature
8-110C; and
Feeding migrations - movements undertaken in search of preferential food (kilka and silverside), in summer and autumn, within the Middle and South
Caspian.
Relation to abiotic environmental factors
Relation to salinity. Brackishwater euryhaline species, inhabits waters with salinity ranging from 0.0 to 13.00/00.
Relation to temperature. Eurythermic species. Endures water temperature from 4 to 250C.
Vertical distribution. Euribathic species found in the areas from the surface layer up to 100 m depth.
Relation to oxygen conditions. Oxyphilic species. Oxygen concentration in water should be no less than 7
mg*l-1.
Relation to fluctuations of the sea level. Decline of the sea level results in reduction of the North Caspian areas, which are utilized as feeding grounds by shad juveniles.
Hence, survival of new generations drops as well as the stock of subspecies as a whole. The rise of the sea level in 2.5 m (1978-2000)
brought the increase of the spawning stock in the Volga River by a factor of 2.33.
Feeding
Feeding type. Heterotrophic
Feeding behavior. Preying and selected/ differentiated food capture
Food spectrum. Euryphagous fish species
Food supply. Zooplankton (15-20%) and fish (80-85%)
Even at fry stage (at 35 mm TL) black-backed shad ingests larval cyprinids and shads (up to 42-87% of the total food weight), feeds also on big and minute forms of zooplankton and benthos:
Copepoda, Cladocera, larvae of Lamellibranchiata, Mysidae,
Cumacea, Corophiidae, Gammaridae (Sushkina, 1940; Matveyeva, 1957).
The bulk of food in the stomachs of adult fish is composed of fish (silverside, kilka, gobies); crustaceans
(Mysidae and Amphipoda) contribute to a relatively small portion.
Quantitative characteristics of feeding. Feeding activity of anadromous shad
during the spawning migration in the river is very low (2.90/000). It increases after spawning:the average index of stomach fullness is
44.10/000, the maximum index - 322.60/000 when
fed on zooplankton and small fish (Vodovskaya, unpublished data).
Reproduction
Reproduction type. Sexual
Eggs and milt are ejaculated by portions into the water column at the river watercourse.
Reproduction areas. Reproduces in the Volga River, from the lower reaches up to the dam of the Volgograd HEPS.
Terms of reproduction. Spawning lasts from May till August. After the first spawning reproduces annually, i.e., spawning interval is 1 year.
Fecundity. Fecundity values are within 53,100-344,000 eggs, 200,000 eggs in average. Relations between individual absolute fecundity (Y, thousand eggs) and characteristics of fish - body length (X1, cm), weight (X2, g), and age (X3, years), are described by regression equations (Vodovskaya, 1979):
Y= 11.352*X1 - 237.65
Y=0.201*X2 + 50.65
Y= 24.325*X3 + 92.58
Limiting factors. The main factors, which rule the spawning efficiency of black-backed shad, are the following:
Number of spawners accessed to the spawning grounds of the Volga River (correlation index K=0.913);
Duration of the Volga River flood period (K=0,67);
Maximum water level in the Volga River during the flood (K=0,621);
Water discharges (flow volume, km3) in April-June (K=0,59).
Lack of the optimum hydrological regime results in decrease of spawning success for this rheophilic species.
Life history and development
Life history stages. Duration of embryonic development is 2 days. Live eggs are large (2.5-4.1mm in diameter), semi-pelagic, floating in the current. Egg membrane is fine and transparent. Perivitelline space within egg is large, 22-33 % of egg diameter. The yolk is semi-transparent, without oil drop (Somova, 1940).
Duration of postembryonic stages:
Prelarva (yolk sac present): 1-5 days
Larva (up to appearing of scales): up to two months
Fry - over 25 mm TL
Juveniles: two-year-old fish
Mature fish: 3-5 years old.
Relation to environmental factors. Eggs and prelarvae floating downstream in the current are the most vulnerable developmental stages.
Age of maturity. Matures at the age of 3-5 years
Thermal conditions of development.
Eggs: 14-250C
Prelarvae and larvae: 15-250C
Fry: 17-250C
Juveniles and adult fish: 8-200C
Quantitative characteristics of growth. The highest growth rate is recorded in the first, second, and third year of life (upon attaining maturity), further growth rate decelerates. The average size of underyearling is 9.6-10.0 cm, in the second year - 18.3-19.4 cm, in the third year - 30.9-31.6 cm.
Age-related weight and length parameters of anadromous shad in the Volga River, 1995-2000
(V.V. Vodovskaya, unpublished data)
Age of fish,
years |
Size (TL, cm) and weight (Wt, g) in age groups |
| Three-year-old |
Four-year-old |
Five-year-old |
Six-year-old |
Seven-year-old |
Eight-year-old |
| Years |
TL, cm |
Wt, g |
TL, cm |
Wt, g |
TL, cm |
Wt, g |
TL, cm |
Wt, g |
TL, cm |
Wt, g |
TL, cm |
Wt, g |
| 1995 |
31.6 |
402 |
35.9 |
613 |
38.0 |
726 |
39.2 |
802 |
41.0 |
925 |
41.8 |
1026 |
| 1996 |
31.2 |
406 |
34.6 |
561 |
37.8 |
740 |
40,0 |
872 |
41.6 |
993 |
44.0 |
1132 |
| 1997 |
30.9 |
388 |
33.9 |
527 |
36.9 |
682 |
39.0 |
816 |
40.2 |
891 |
42.5 |
1097 |
| 1998 |
31.4 |
415 |
34.5 |
547 |
37.3 |
696 |
39.2 |
821 |
41.3 |
969 |
42.2 |
986 |
| 1999 |
31.4 |
410 |
35.7 |
618 |
38.0 |
751 |
39.5 |
852 |
40.9 |
940 |
42.2 |
1069 |
| 2000 |
31.3 |
395 |
35.0 |
592 |
38.6 |
789 |
40.6 |
936 |
41.8 |
1034 |
44.0 |
1162 |
Structural and functional population characteristics
Sexual structure. Sexual composition of the spawning stock changes with years, the proportion of males varies from 35 to 61 %, females - from 39 to 65%.
Age-size structure. Specimens aged 3-8 years take part in spawning. Mean age is 4.5 years, TL - 22-46 cm, 35-36 cm on average.
Age composition (%) of black-backed shad in the Volga River, 1995-2000
(V.V. Vodovskaya, unpublished data)
| Years |
Age, years |
| Three-year-old |
Four-year-old |
Five-year-old |
Six-year-old |
Seven-year old |
Eight-year-old |
Mean age |
| 1995 |
5.2 |
48.4 |
32.5 |
11.6 |
1.9 |
0.4 |
4.58 |
| 1996 |
12.4 |
41.0 |
31.5 |
11.7 |
2.8 |
0.6 |
4.50 |
| 1997 |
12.2 |
38.8 |
31.3 |
13.6 |
3.2 |
0.9 |
4.60 |
| 1998 |
11.3 |
40.4 |
31.8 |
12.4 |
3.1 |
1.0 |
4.60 |
| 1999 |
- |
24.0 |
43.1 |
25.1 |
6.5 |
1.3 |
5.20 |
| 2000 |
0.4 |
32.0 |
27.1 |
22.0 |
6.6 |
1.6 |
5.90 |
Quantitative characteristics. In 1990-1999, the number of spawners varied between 4.640 and 12.893 million specimens. In 1976 - 1995, investigations in the North Caspian showed increase in catch per unit (simulated per 100 drift nets) from 34.1 to 71.0 kg.
Population trends. The current high water level of the Caspian Sea favors enhanced abundance of black-backed shad due to the good feeding conditions for juveniles at large areas of the North Caspian.
Interspecific relations
Larval shad is prey to fish and even invertebrates (Cyclops). Juvenile and adult shad are consumed by predatory fish species (catfish, beluga, zander, pike, asp, etc.), as well as seal and piscivorous birds (cormorant, big white heron, and little tern).
At present, black-backed shad is not an abundant species of the Volga-Caspian basin; hence
its preying on kilka, silverside, and gobies does not affect their number significantly.
Importance of subspecies to bioresources production of the Caspian Sea
Economic significance of subspecies. Black-backed shad is an extremely important fisheries item. It is the biggest shad in the Caspian, with high fat content - up to 19%.
It is processed as canned food, salted and pickled fish of top quality.
Commercial characteristics of subspecies, catches. In 1984-2000, the catch of migratory shad amounted to 806-4,310 tons, 1,700 tons in average. Before regulation of the Volga River flow the catches varied between 3,340 and 31,300 tons, an average catch was 5,300 tons.
Fishing gears and fishing zones. Fishing is carried out with beach seines during
shad spawning migration (in April) at the experimental fishing sites of Azerbaijani and Dagestan coasts. The main harvesting of black-backed shad is conducted in the Volga River delta from the end of April till June.
Impact of fisheries on the population status
As no selective fishing methods exist at the moment, prolongation of fishing season (for semi-anadromous fish species) results in decline of the spawners' number extracted as bycatch, and thus affects efficiency of shad reproduction.
Human impact/Threats. In spring and summer, hydrological regime in the Volga River should be adjusted to conditions favorable for spawning migration, development of semi-pelagic eggs, and downstream migration of larvae
((low current, flow velocity less 2 m*sec-1, exclude Cyanophyceae bloom).
Contamination with heavy metals, chlororganic substances, and oil pollution are disastrous to black-backed shad, which needs clear
water throughout its life.
Conservation measures. The main condition for existence of this subspecies is availability of pure water within the whole area of its distribution.
References
Berg, L.S. 1913 . Caspian shads sampled during the expedition of 1912 along the western coast . The materials for perception of Russian fishery. Vol.2, 2:1-50.
Braginskaya, R.Ya. 1957. On the question of the development of black-backed shad and Volga River shad. Proc. Severtsov Institute of Animal Morphology. USSR AS, 16:171-180.
Grimm, O.A. 1887. Astrakhan shad. "Farming and Forestry". Pp. 7-43.
Kessler, K.F. 1870. On the fish of order Clupeiformes occurring in the Volga River . Proc. St.-Petersburg Society of Naturalists. Vol. 1,1: 235-310.
Matveyeva, R.P. 1957. Feeding of young shads in the Northern Caspian . Trans. Hydrobiological Society. 8:368-386.
Pallas, 1771. Reise ,III: 489.
Piskunov, I.A. 1961. On nutritional relationships between some commercial fish species of the Caspian Sea. Voprosy Ikhtiologii (Problems of Ichthyology). Vol.1, 1(18): 79-88.
Svetovidov, A.N. 1943. On the Caspian and Black-Sea shads of the genus Alosa and on the conditions of their speciation . Zool. Journ. Vol.22, 4:222-232 .
Somova, S.G. 1940. Development of black-backed shad Caspialosa kessleri Gr. Proc. VNIRO. Moscow. Pp.149-170.
Sushkina, A.P. 1940. Feeding of migratory shad larvae in the Volga River. Proc. VNIRO.14:171-210.
Vodovskaya, V.V.1979. On maturation and fecundity of the black-backed shad
(Alosa kessleri Grimm) Proc. VNIRO.133:122-131.
Compiled by:
V.V. Vodovskaya, CaspNIRKH, Astrakhan, Russia