State and dynamics of commercial fish stock recruitment in the lower Dniprо river

Purpose. To find qualitative and quantitative parameters of juvenile fish communities as a basis for commercial fish stock and biological diversity in the Dniprо-Bug ria system. Methodology. Primary data were collected during summer-spring period 2006-2015 from catches of small-mesh fishing gears for catching juvenile fish such as beach seine and trawl. In total, catches of 375 stations were analyzed; the total hauled area was more than 50 thousand m2 of littoral shallow waters. To characterize commercial catches, the data of official fishery statistics. Data collection and processing were performed according to generally accepted methods. Findings. The data on species composition, abundance and distribution of juvenile fish communities in the Dnipro-Bug ria system has been selected and analyzed. Major trends in the dynamics of catches of fish juveniles per unit effort as an integral feature of natural reproduction and basis for the recruitment of commercial fish stocks have been detected. Reproduction conditions of various ecological groups of fishes have been studied. The dynamics of the qualitative composition of commercial catches has been analyzed. Last years, the majority of commercial catches in the Dnipro-Bug ria system consists of Black-sea sprat (62.2%) and Prussian carp (21.4%); the category of “valuable commercial species” composed 7.3% of the total catch. Self-reproductive fish populations ensured formation of 93.5% of the total catch. i.e. natural reproduction remains the major source of the recruitment of commercial fish stocks in the Dnipro-Bug ria system. According to the data of studies of 2006-2015, juveniles of 18 fish species were recorded in the littoral zone, the majority of which (56.3-57.2%) were low value and secondary species – Prussian carp, Black-sea sprat, atherina. Among valuable commercial species, the most abundant were roach (7.3%) and bream (3.4%); at the same time, these species formed 16.4% of the total catch in gill nets in 2010-2017. The inter-annual dynamics of the abundance of juveniles of commercial fish species during last 10 years has been characterized by positive trends that under condition of the maintenance of optimum hydrological regime of the Dnipro-Bug ria system indicates in the possibility of ensuring stable commercial catches in the nearest future. Originality. The data on the structure of juvenile fish communities of the lower reaches of the Dnipro river as a component of fish fauna of the Dnipro-Bug ria system have been provided. A detailed description of the dynamics of the number of juveniles of major commercial fish species in an inter-annual aspect has been provided. Practical value. The obtained results have been used for the development of long-term prognoses of fish productivity parameters as a basis for the regulation of qualitative and quantitative parameters of commercial fishing pressure and conservation measures.