Stizostedion lucioperca, (L.)

Taxonomic description of species

Pelvics thoracic, under pectorals. Dorsals 2, obviously separated. D XIII-XVII, I-III 19-24. Upper jaw extends beyond posterior edge of eye. Preopercle bare or partially covered with scales. Large canines on jaws.
Intraspecific forms. Two separate stocks exist in the North Caspian basin: the Volga and the Ural River stocks, their marine habitats are hardly differentiated due to the common feeding areas.
Related forms: Stizostedion volgensis (Gmelin, 1788) � Volga zander, bersh; Stizostedion marinum (Cuvier, 1828) � sea zander; North American zanders: Stizostedion vitreum � walleye, and Stizostedion canadense � sauger

Distribution within the Caspian Sea

The species is distributed within the North Caspian, estuarine areas of the Volga, Ural and Terek rivers, the Kura River drainage, lower reaches of the Araks River, the Divichinskiy firth, the Kumbashinka River, the Sefid-Rud river, Enzeli bay.
Status as per International Red Data Book: N/A
Status as per National Red Data Books: N/A
First record for the Caspian: Kessler, 1877
Redescription of species: Perca lucioperca Linnaeus, 1758:289; Lucioperca sandra Cuvier, 1828:110; Lucioperca sandra Kessler, 1864:22; Lucioperca lucioperca Berg, 1905:224; Stizostedion lucioperca Banarescu, 1964:670

General characteristics of species

Ecologo-taxonomic group. Nekton
Origin. Freshwater species
Distribution. Widely distributed through the Middle and Eastern Europe. Found everywhere in the rivers and lakes of the Baltic, Black, and Aral Sea basins.
Habitat. Inhabits desalinated/ freshened zones of the sea. Keeps in the areas devoid of vegetation, with good oxygen conditions. The semi-anadromous zander migrates upstream the Volga River for spawning at a distance of 200-300 km, in the Ural river � at a distance of 150-200 km from rhe river mouth..
Migrations. Spawning migration occurs in spring as soon as ice melts. Wintering migration starts in autumn, fish aggregates in deep pockets in the delta. Feeding migrations take place in summer, fish move to desalinated sea areas.

Relation to abiotic environmental factors

Relation to salinity. Brackishwater stenohaline species (less 12�)
Relation to temperature. Stenothermic cool-water species
Vertical distribution. Stenobathic species. In the North Caspian prefers areas of moderate and minor depths (4-6 m).
Relation to oxygen conditions. Oxyphilic species. Intolerant to hypoxia; for this reason zander frequently leaves the western part of the North Caspian and migrates to the eastern areas with more favorable oxygen conditions.
Relation to fluctuations of the sea level. The drop of the sea level leads to reduction of feeding areas for the species in the North Caspian, consequently, to degraded conditions for production and decrease of commercial stocks.

Abundance of zander juveniles in the North Caspian under conditions of varying water discharges of the Volga River

Feeding

Feeding type. Heterotrophic, holozoic
Feeding behavior. Active preying and food capture
Food spectrum. Stenophagous predatory species. Feeds on zooplankton at early stages of development, further (at 15-20 cm TL) shifts to fish diet.
Food supply. Feeds on fish, primarily, cyprinids, seldom - on benthos (Trichoptera larvae), nekto-benthos (Mysidae). Zander is the main consumer of the Caspian roach (Shorygin, 1952; Vasilchenko, 1968; Orlova, 1976; Yanovskaya, 1976).
Quantitative characteristics of feeding. Annual food consumption - appr. 6.1 kg. In mid-1960-s - 1970-s, when zander stocks were estimated equal to 7 million individuals, the total predation on the Caspian roach composed 53.0 thousand tons.

Reproduction

Reproduction type. Sexual. Spawning (annual) of cyclic type. Zander is referred to phytophilic group; eggs are deposited on vegetation, in the nests at the depth 30 - 200 cm.
Reproduction areas. In the Volga-Caspian area the most part of the population reproduces in the riverine channels and shallow side streams at the lower zones of the Volga-Akhtuba floodplain; in Ural River - at the sides of the main watercourse and its branches.
Terms of reproduction. Reproduces in April and in the first 10 days of May at water temperature 7-12^oC.
Fecundity. Fecundity ranges from 14.6 to 350.9 thousand eggs. Eggs are small, egg diameter is 1.5 mm.
Limiting factors.
Biotic factors:

• abundance of breeders,
•  food supply during the period of juveniles feeding,
• abundance of predatory fish and invertebrates.

Abiotic factors:

• thermal conditions during spawning and feeding of juveniles,
• concentration of dissolved gas, water discharges in the river providing favorable feeding conditions for juveniles in spring and summer.

Life history and development

Life-history stages
1^st � embryonic period
2^nd � prelarval period, TL 4.5 - 6.2 mm
3^rd � early larval period, TL 6.2 � 12.3 mm
4^th � late larval - early fry period, TL 12.3 - 36.0 mm
5^th � fry - fingerling period, TL 36.0-170 mm
Relation to environmental factors. The threshold oxygen concentration for the embryos is 5-6.5 mg O₂*l^-1. Total mortality of larvae is observed at concentration 1.3-2.4 mg O₂*l^-1. Water salinity should not exceed 10�, the lower optimum limit - 3 �. pH value at the spawning grounds � within 7.2-8.4. Optimal water temperature: 11.5-22⁰C.
Age of maturity. Males mature at the age of 2 years, females - at 3 years.
Thermal conditions of development. Eggs develop at water temperature 7-12^oC, prelarvae - at 10-15^oC, early larvae � at 12-18^oC, late larvae � at 15-22^oC, fry and fingerlings - at 18-24^oC.
Quantitative characteristics. By the end of the first year juveniles attain 20-25 cm TL, weight - 180-200 g; two-year-old specimens - 30-34 cm TL, weight - 300-560 g; three-year-old fish - 35-40 cm TL, weight - 600-900 g; four-year-old fish - 43-44 cm TL, weight - 800-1.200 g; five-year-old fish � 47-49 cm TL, weight - 1.500-1.600 g.

Linear and weight characteristics of zander in the Volga River delta

Structural and functional population characteristics

Sexual structure. Sex ratio at the peak spawning is close to 1:1; thereupon the number of females increases. Sex ratio equalizes in summer and autumn. Proportion of females varies annually from 35 to 55%.

Qualitative characteristics of spawning population of zander from the River Ural

Qualitative characteristics of spawning population of zander from the Volga River

Males mature at an earlier age, hence they prevail in the junior age groups of commercially exploited part of the stock; females prevail in senior age groups.
Age-size structure. Zander can reach the length of 70 cm, 4 kg in weight. In 1973-1979, zander from the Ural River was 38-55 cm TL (mean TL - 46 cm), 0.6-1.8 kg in weight (mean Wt - 1.26 kg). Prevailing age groups - 3-6-year-old fish (Petrova, 1981). Zander from the Volga River is generally smaller
Quantitative characteristics. The number of zander specimens assessed for the Ural River in 1999 amounted to 41147, commercial stock was estimated as 7.64 thousand tons. Commercial stock of the Volga river zander accounted for 4.3 million individuals in 1999, commercial reserve - 2 thousand tons (Kushnarenko, 2001).
Population trends. The species abundance reveals annual fluctuations dependent on the yield of generations presented in the catches. The main factors, which impact the population number, are: the level of the sea, the volume of freshwater discharge, oxygen conditions in the North Caspian, unsustainable fishing and poaching

Interspecific relations

Zander is a food competitor to the other predatory fish species including beluga.

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. A valuable commercial fish, among the most important semi-anadromous fish species in the Volga and Ural fisheries
Commercial characteristics of species, catches. Up to the mid-1960-s, the maximum catches were recorded at the Volga River. Corresponding to reduction of commercial stocks the catches at the Ural River in some years exceeded those at the Volga. In 2000-2001, zander catches at the Volga River composed 1,000 tons. 
Fishing gears and fishing zones. In the lower reaches of the Volga and Ural fishing is carried out with riverine beach seines. Fixed nets and trap nets are used mainly in the Volga fore-delta and coastal waters.

Impact of fisheries on the population status

Overfishing causes decrease of population number. At present, intensive exploitation of the Volga and Ural River stocks requires implementation of measures aimed to recovery of species abundance.
Human impact/ Threats. This fish is extremely sensitive to oxygen concentration in the water as well as to various types of water contaminationincluding oil/ hydrocarbon pollution. 
Conservation measures

1. Reinforce fish protection activities;
2. Observe Fisheries Regulations, prohibit the use of fine-meshed riverine beach seines in autumn, which cause capturing of small-sized zander (fingerlings);
3. Establish favorable regime of water discharges in the Volga river; carry out fishery melioration of spawning grounds in the Ural river; enhance artificial propagation of the species.

References

Berg, L.S. 1961. Selected works. Vol. 4. Ichthyology. Moscow-Leningrad. P. 25.
Koblitskaya, A.F. 1981. Inventory on freshwater young fish. Food and Light Industry. Moscow. pp.154-161.
Kushnarenko, A.I. 2001. The present state of the stocks of the Volga river zander. The book of abstracts "The state of stocks of the commercial objects in the Caspian sea and their use. Astrakhan, pp. 272-280.
Orlova, E.L. 1976. The feeding of the predatory fish in the delta-front of the Volga River. Hydrobiological J. Vol. 12, 2: 54-61.
Petrova, A.N. 1981. Abundance trends and the sustainable management of the stocks of the Ural River semi-migratory zander in the basin of the Northern Caspian. Author's Abstracts of the Ph. D. Dissertation. Leningrad. 22 p.
Shaposhnikova, G.Kh. 1964. Biology and fish distribution in the rivers of the Ural basin. Nauka. Moscow.
Shorygin, A.A. 1952. Feeding and food relations of fish in the Caspian Sea. Moscow. 267 p.
Vasilchenko, O.N. 1968. Feeding of predatory fish during the downstream migration of young fish from the low-lying flood plains flooded and breeding farms of the Volga River delta. CaspNIRKH Proceedings. Vol. 24.
Yanovskaya, L.I. 1976. The feeding of zander in the Northern Caspian. VNIRO Proceedings. Vol. 117, pp. 34-46. 

Compiled by:

I.M. Aminova (KazNIIRKh Atyrau branch, Kazakhstan)
A.I. Kushnarenko (CaspNIRKh, Astrakhan, Russia)