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

Results of ichthyological surveys of the main commercial fish species of the Dnieper R. and Desna R. within Chernihiv Region (Ukraine) were analyzed; biological parameters, which characterize the state of commercial fish stocks, were determined. The data of commercial catches, official fishery statistics, and results of monitoring surveys performed by Ichthyological Service of Chernihiv Fish Protection Inspection in 2015 were used as research materials. Ichthyological samples were collected from gill net catches during spring-summer period. Totally, 1,191 specimens of different fish species were analyzed. The total mortality coefficient (Z) was determined by graphical method with the use of natural logarithms of age group number in monitored catches. Natural mortality was estimated for mean age groups according to P.V. Tyurin. Altogether, 19 fish species have been recorded in the Dnieper R. and Desna R. within Chernihiv Region for the last five years; the main 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 fish existence conditions, mortality values of the main commercial fish species have been established. According to the results of age-length structure of bream, roach, silver bream, pikeperch, pike and Prussian carp stocks, total mortality coefficients varied within 0.36–0.64; natural mortality -- 0.18–0.44; fishing mortality did not exceed 0.20. Parameters, characterizing the state of recruitment and exploitation of the 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. The obtained data have been used for the development of the total allowable catches of aquatic living resources in the Dnieper R. and Desna R. for 2017–2019.