Current state of commercial fish fauna of the Dnipro river and Desna river within Chernihiv region

Purpose. To analyze the results of ichthyological surveys of major commercial fish species of the Dnipro river and Desna river within Chernihiv region and determine the biological parameters, which characterize the state of commercial fish stocks. Methodology. As input material, the data of commercial catches and results of monitoring surveys performed by Ichthyological Service of Chernihiv Fish Protection Inspection in 2015 have been used. Ichthyological material was collected from gill net catches during spring-summer period. In total, 1191 specimens of different fish species were collected for biological analysis. Collection and processing of the material was performed according to generally accepted methods. The total mortality coefficient (Z) was determined by graphical method with the use of natural logarithms of age group numbers in monitoring catches as a tangent of the regression line. The natural mortality was determined for mean age groups according to P.V. Tiurin. The data of official fishery statistics were used for the work. Findings. In total, 19 fish species have been recorded in official commercial fishery statistics in the Dnipro river and Desna river within Chernihiv region during last five year; major commercial species were bream (22.9…44.5% of annual total catch), silver bream (24.5…24.7%), roach (14.9–15.4 %), and blue bream (3.3-12.1%). As an integral feature of the conditions of fish existence, the mortality values of major commercial fish species have been established. According to the results of age-length structures of bream, roach, silver bream, pikeperch, pike and Prussian carp stocks, the total mortality coefficients varied within 0.36–0.64; natural mortality ― 0.18–0.44; fishing mortality did not exceed 0.20. As a whole, the parameters, which characterize the state of recruitment and exploitation of studied populations, were at a level inherent to middle-cyclic species with increased natural mortality (excluding bream, roach, and silver bream), sufficient recruitment and moderate level of commercial exploitation. Originality. For the last 10 years, a detailed analysis of the length structure of major species of commercial fish fauna of the Dnipro river and Desna river was performed and integral parameters characterizing the conditions of forming and exploitation and their stocks were determined. Practical value. The obtained data were used for the development of allowable catches of aquatic living resources in the Dnipro river and Desna river for 2017–2019.