Taxonomic description of subspecies
Body length (TL) 6.0 � 12.8 cm, mean value - 7,8 cm. Body comparatively deep, maximum depth 15.5-23.5% of
TL, 19.7% in average. Head moderate, in average, 21% of TL. Mean eye diameter - 25% of head length. Lower jaw slightly extended. Ventral scutes well developed. Pectorals and pelvics long, pectorals 17.7-21.2% (average 12.7%) of
TL, pelvics � 11.7-13.8% (average 12.7%) of TL. Gill-rakers: 51-62, 60 in average. Vertebrae 40-43, 41 in average. The back and the upper part of head vary in color from light green to blue-green, abdomen silvery white or golden yellow.
Intraspecific forms. Kilka or sprat is a subspecies of Black sea-Azov sprat
Cl. cultriventris (Nordmann, 1840). It differs from typical Azov-Black sea sprat with bigger body sizes correspondent with less depth, short pectoral fins, less number of gill rakers. Wide adaptive plasticity of kilka at different stages of its life cycle contributes to differentiation of this species into smaller groups isolated reproductively. Differences between the groups estimated according to genetic markers, reveal certain correlation with biological characteristics of species.
Related forms. Clupeonella abrau (Maljatskij, 1930) � Abrau sprat
Clupeonella engrauliformis (Borodin, 1904) � anchovy sprat
Clupeonella grimmi Kessler, 1877 � big-eyed sprat
Distribution within the Caspian Sea
Distributed throughout the sea, mostly inhabits shallow zones and does not descend the depths more than 100 m. During the period of sea transgression, feeding areas of kilka extended in the Middle and South Caspian. Enters the Volga, Ural and Terek rivers.
Status as per International Red Data Book. Introduced in IUCN Red List, DD.
Status as per National Red Data Books: N/A
First record for the Caspian. N.A.Borodin, data of the First �clupeid� expedition to the Caspian, 1904
Redescription of subspecies: None
General characteristics of subspecies
Ecologo-taxonomic group. Pelagic fish/nekton
Origin. Caspian autochthon
World distribution. Ponto-Caspian endemic species
Habitat. Pelagic zone
Migrations. Spawning, wintering, feeding.
Spawning migration to the North Caspian starts in March and continues through April-May. The majority of stocks migrate along the western coasts, approach Chechen and Tyuleniy islands, than move northward to the western part of estuary; the other part turns north-east and completes migration at Buzachy and the mouth of the river Ural.
Relation to abiotic environmental factors
Relation to salinity. Euryhaline subspecies.
High euryhaline ability is confirmed by the fact the species inhabits both fresh waters and zones with maximum Caspian salinity (e.g., former Kaidak bay). The biggest concentrations are recorded in zones with salinity ranging from 3 to 7�. Increased salinity (up to 12�) during low water period is supposed to be one of the main factors, which affected decrease of the kilka survival. The most intensive spawning occurs at salinity values 2-4�.
Relation to temperature. Eurythermic subspecies.
Occurs at surface temperature range 2.6-26oC. The basic part of population distributes in waters at temperature 18-20oC.
Vertical distribution. Eurybathic.
Relation to oxygen conditions. Oxyphilic subspecies.
Occurs in well-aerated water, frequently over-saturated.
Relation to fluctuations of sea level. Rising sea level, which started in 1978, resulted in extension of species spawning area and increased abundance (r=0.78). This relationship is described by regression equation:
P=11.89 * U0.87,
where: P � abundance of fingerlings
U � sea level
Long-term dependence of juveniles� survival on annual water discharges was revealed mostly during low water level period (1973-1977), when survival was low at its minimum (9.5%). Rise of sea level in 1978-1990 led to increased survival by the factor of 8.
Feeding
Feeding type. Heterotrophic (live organic substance)
Feeding behavior. Preying and selected capture of food items.
Food spectrum. Euryphagous species. Food spectrum contains up to 34 components: Copepods - 8 taxa, Cladocera - 11 species, Rotatoria - 2 species, planktonic stages of Balanus and mollusks, crayfish and other components.
Food supply. During last years, the biomass of Copepods, the main food item of kilka, reduced to 35% of total plankton biomass in the North Caspian.
Quantitative characteristics of feeding. The daily diet of North Caspian kilka comprises 4.95% of body weight, South Caspian kilka � 5.35% of body weight. Average daily food consumption (per one specimen) � 0.163 g, North Caspian stock, 0.223 g , respectively, in the South Caspian stock.
Reproduction
Reproduction type. Sexual
Reproduction areas. Local stocks are differentiated by spawning areas in the sea. The most abundant is the North Caspian stock due to large areas of shallow freshwater zones, and high biological productivity of the northern part of the sea dependent on nutrient inflows of the Volga and Ural rivers. The main spawning areas in the North Caspian are located between the islands Chistaya Banka and Maly Zhemchuzhny, under the influence of the Volga streams, the depths do not exceed 5-7 m. Spawning of southern kilka takes place in the coastal zone along the eastern and western shores of the South Caspian and its bays as well as the western coast of the Middle
Caspian.
Terms of reproduction. North Caspian kilka starts spawning in April and continues until late June, its peak is observed in the first 10 days of May at water temperature
14-19oC, depth - 1-6 m. In May, spawning takes place in the coastal areas, in June - mostly in
waters 5-6 m deep. In the southern part of the sea spawning starts in February.
Fecundity. Fecundity varies from 9.5 to 60 thousand eggs (31.2 thousand eggs in average). Estimated population fecundity of the South Caspian stock -
140*1013 eggs, North Caspian stock, respectively, � 180*1013 eggs.
Limiting factors. Strong correlations between productivity values and the number of days with water temperature
14oC (optimal for eggs development), and favourable wind conditions were revealed (r=0.88, r=0.78, respectively). Productivity is
as well affected significantly by the Volga inflow (r=0.67), which determines biological productivity for the whole North Caspian; 240-300 km3/year runoff enables optimal survival of juveniles.
Life history and development
Life history stages. Batch spawning. Small-sized pelagic eggs are 1 mm in diameter, with a large oil drop occupying about 1/3 of egg diameter, and considerable perivitelline space. Eggs retain in the water column owing to the oil drop. Depending on water temperature hatching occurs
in 27-30 hours after spawning. Larvae are 1.3-1.8 mm TL with big yolk sac. By September, fingerlings reach 50-55 mm TL.
Relation to environmental factors. Early ontogenesis proceeds in surface layers above the depths 1-7 m, where the most abrupt fluctuations of water temperature and surge occur. Storming conditions at sea decrease survival of embryos and larvae due to hydrodynamic wave impacts. Temperature range providing for the best survival of embryos and larvae is restricted to
14-19oC. Eggs and larvae are found at comparatively wide salinity range, 0.02 - 15�. Regression/ correlation analysis reveals a strong relation
(r=0.89) between fingerlings abundance (P), sea level (N), Volga runoff (V), water temperature (T), and zooplankton biomass (Pl.):
P=0.2228*N+0.01180*V*0.3 + 0.217102 T*0.3+0.0628*PL � 0.422096
Age of maturity. Matures at an earlier age than the other related species. Most individuals mature at the age of 1 year, 45-70 mm TL. Population structure is characterized by high abundance of recruitment and low abundance of the remainder.
Thermal conditions of development. Correlation between water temperature and abundance of fingerlings (r=0.76) is estimated as,
Y = 0.08610.19x, where
y � kilka productivity, individuals per hour
x � water temperature
The largest number of larvae was recorded in the last 10 days of May at water temperature
18-20oC.
Quantitative characteristics of growth. Linear growth rate depends on development of food organisms, North Caspian areas and water temperature at feeding grounds. Linear growth rate is described by I.I. Shmalgauzen growth equation (1957):
L= 30.2t0.18058 , where
L � individual length at t age
t � age in days.
Relation between length and weight in juveniles is as follows:
W = 0.13Lt0.3218, where W � individual weight.
Based on the above equation, weight growth rate is described as:
W = 0.154 t1.034
The most rapid growth rate is recorded at the first month of life. During this period, sizes increase from 1.3-1.8 mm (newly hatched larvae) to 30.4 mm, i.e. almost 20-fold. During the second month, total (absolute) increment comprises 12.1 mm, 9.8 mm � over the third month. In July, average size amounted to 30.4 mm in the west, 28.6 mm in the east; in August � 42.5 mm and 40.9 mm, in September � 52.3 mm and 51.4 mm, respectively.
Length-weight growth in adults was calculated on the basis of long-term data using Shmalgauzen growth equation (1935):
L = 0.51 t0.18058
W = 2.2 t0.6819, where
L � length (cm), W � weight (g), t � age
The maximum linear increment is recorded during the first year of life, weight � during the second year. The North Caspian kilka grows slower than that in the South Caspian. During the first year of life, Southern Caspian kilka attains the average size of 6.5 cm, North Caspian � 5.3 cm. Males grow slower than females, the most significant growth discrepancy is observed at the age of 2-3 years.
Structural and functional population characteristics
Sexual structure. Males prevail (69.5%) over females both within the North Caspian population in the whole and in all age groups. Long-term sex ratio in the South Caspian stock is close to 1:1, males predominate insignificantly in spring (50.6%), females - in autumn (51.5%).
Age-size structure. The North Caspian specimens taken from trial catches had 7.1 cm mean length, 3.1 g weight, mean age � 2.1years; respective values for the South Caspian specimens � 7.9 cm, 4.3 g; 2.4 years. The maximum length and weight of kilka are 14.5 cm and 19 g. Maximum age of kilka is reported to be 6 years. Age structure includes up to 6 generations. Age composition varies depending on recruit stock number, altogether, 1-, 2-, 3-year-old fish prevail, they yield to the average 87.5% of the total. In the whole, kilka population is characterized by high abundance of recruitment compared with the rest/ remainder.
Quantitative characteristics. The total abundance in 2000 was calculated to be 224 billion individuals; North Caspian stock � 128 bn ind., biomass - 236.1 thousand tons; South Caspian stock � 96 bn ind., biomass � 218.0 thousand tons. During the last 20 years, total biomass varied from 203.5 to 455.6 thousand tons.
Population trends. Decline of Copepods biomass (the main food item) resulted in degraded habitat conditions in the North Caspian and slightly decreased abundance of the North Caspian stock. At the same time, abundance of the South Caspian kilka increased. Notably, during the last years, the numbers of both stocks tend to equalize, while in the former years the North Caspian stock contributed to 75% of total abundance.
Interspecific relations
Kilka occupies a significant place in the Caspian ecosystem; on the one hand, as the basic consumer of zooplankton, on the other hand, as a producer for predatory marine fish and seal.
Importance of species to bioresources production of the Caspian Sea
Economic significance of species. For a number of years common kilka was not harvested, however, recent data confirm it is feasible prospective commercial species for Russian fisheries. Even though 60% is consumed by predators, there exists certain reserve
in its stocks.
Commercial characteristics of species, catches. No fishing
Fishing gears and fishing zones. N/A
Impact of fisheries on the population status
N/A
Human impact/Threats. Currently, increased concentrations of phenol, heavy metals, oil and multiring
aromatic hydrocarbons were recorded in the surface waters of the South and Middle Caspian. Contamination of the Caspian Sea may attribute to the chronic toxicosis in kilka. In the year of 2000, an outburst of Mnemiopsis abundance, a severe competitor to plankton-feeding fish, was recorded in Caspian Sea.
Conservation measures. Urgent measures need to be undertaken to control Mnemiopsis abundance.
References
Aseinova, A.A. 1992. Common kilka. In: Scientific grounds for regional distribution of commercial species in the Caspian Sea. Fishery concern Kaspryba. CaspNIRKH. Astrakhan
Aseinova, A.A. Common kilka in the Caspian Sea. Ichthyofauna and commercial resources. Nauka. Moscow pp. 71-80.
Kazancheev, E.N. 1981 Fish of the Caspian Sea. Light and Food Industry. Moscow.
Svetovidov, A.N. 1952. Herrings (Clupeidae). Series "The USSR Fauna". Vol. 11, 1: 223. AN USSR AS Press. Moscow-Leningrad p. 223.
Shmalgauzen, I.I. 1935. Growth and general body sizes in view of their biological significance. Growth of animals. Moscow pp. 8-61.
Compiled by:
A.A. Aseinova, (CaspNIRKh, Astrakhan, Russia)