Dynamics of structural and biological indicators of the spawning stock of arctic cisco Coregonus autumnalis from the Yenisey river at different fishing intensity

Arctic cisco is a valuable commercial species. It is one of the main fishing objects in the lower reaches of the Yenisei River. Since the beginning of the 2000 s , there has been a decrease in biological indicators and the number of spawning stocks of this species in the Yenisei River, in connection with which, since 2019, restrictions have been established on the harvest of the Yenisei population of Arctic cisco for all types of fishing with the exception of fishing for research and aquaculture purposes. The research analyzes changes in the main biological indicators of the spawning stock of Arctic cisco in the Yenisei River (age and size composition, standard length, weight, absolute fertility) in the period from 1986 to 2023. Particular attention is paid to the connection between the biological parameters of the herd and the intensity and specificity of fishing for this species in different years. A significant decrease in the average values of fecundity, standard length, body weight and age of fish in the spawning stock was noted in the period 2008–2018, in comparison with data for 1986–2007, which is associated with the reorientation of fishing from the feeding part of the population to the spawning one and, as consequence, an increase in fishing mortality of sexually mature individuals. Based on materials collected in 2019–2023, there is an increase in the average values of standard length and weight of fish in the spawning stock; however, these indicators are still lower than the values of 1986–2007.