Modern state of the reproductive potential of Black Sea sprat Sprattus sprattus phalericus (Risso, 1826) (Pisces: Clupeidae) in Crimea region and conditions for its formation Preliminary version

Main Article Content

G. V. Zuyev

http://orcid.org/0000-0003-4164-1288

https://elibrary.ru/author_items.asp?id=805873

Abstract

Black Sea sprat Sprattus sprattus phalericus (Risso, 1826) is one of the abundant species of fish in the Sea of Azov – Black Sea basin. Due to its large number sprat plays an extremely important role in the ecosystem of the sea, being an intermediate link between zooplankton and representatives of the highest trophic level – large predatory fish, dolphins, and birds. At the same time sprat is one of the important commercial fish in all the Black Sea countries, steadily being on the second place of catch volume  in recent decades (after anchovy). The total catch reaches 100 thousand tons. Turkey and Ukraine are the main producing countries. Monitoring and forecast of biological state of the sprat population with rising fishing intensity and climate changes are urgent tasks. The research subject of this article is the long-term (2000–2016) dynamics of biological (qualitative) parameters determining the population fecundity (reproductive potential) of Black Sea sprat in Crimea region, the current state of reproductive potential, and the conditions for its formation. The article is based on the results of own research. Parameters determining the population fecundity – the length-age structure of the spawning part population, the sex structure population (ratio between females and males), the absolute individual fecundity – were studied. In the long-term plan (in 2011–2016 compared with 2000–2004) the average length of spawning females decreased by 1.22 times (from 7.36 to 6.03 cm). It was accompanied by a decrease in the absolute individual fecundity by 2.39 times (from 13625 to 5690 eggs). The numerical ratio between females and males decreased by 1.23 times (from 1.95 to 1.59). Simultaneously the sprat stock in the northern part of the Black Sea was reduced by more than 2.5 times (from > 500 thousand tons to < 200 thousand tons). As a result, the population fecundity of sprat in Crimea region decreased by more than 7 times (2.39 × 1.23 × 2.5). The conditions of sprat fishing in the northern part of the Black Sea (from the mouth of the Danube to the Kerch Strait) were studied. They showed 2-fold (from 251.9 thousand tons in 2000–2004 to 129.1 thousand tons in 2011–2016) decrease in the total catch and more than 2.3-fold (from 50.4 to 21.4 thousand tons) decrease in average annual catch in this region. On the contrary, in the Crimean shelf the total catch at that time increased by 1.2 times (from 76.9 to 92.2 thousand tons), and its average annual value remain constant (15.39 thousand tons in 2000–2004 and 13.37 thousand tons in 2011–2016). While reducing the stock by 2.5 times, this means that the fishing pressure on the Crimean population increased 2.5 times. This fact suggests considering the factor of fishing as the main cause of its degradation. Validity of this version is confirmed the fact of conjugacy (inverse connection) of interannual fluctuations between the catch and length-age parameters of sprat in the Crimean region in 2003–2013 previously found: catches over 15–16 thousand tons were accompanied by a decrease in the fish average length and average age displaced regarding year of catch by one year ahead. Regulation of fishing is the necessary condition for preventing further degradation, for restoring and maintaining sustainable state of sprat population in the Crimean region and its reproductive potential. The negative impact of natural (climatic and trophic) factors on the state of the population should be considered as a secondary factor. Local overfishing indicates the structuring of the commercial stock of Black Sea sprat, its division into a number of geographical sustainable aggregations (stock units), i. e. the presence of intraspecific differentiation.

Article Details

ZuyevG. V. Modern state of the reproductive potential of Black Sea sprat Sprattus sprattus phalericus (Risso, 1826) (Pisces: Clupeidae) in Crimea region and conditions for its formation. Marine Biological Journal, 2019, vol. 4, no. 4, pp. 3-14. doi: 10.21072/mbj.2019.04.4.01
Keywords:
sprat, long-term dynamics, fecundity, population structure, fishing, stock
Section
Scientific communications

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