Change in the state of an exploited fish population: From individual indicators to integral assessment

Abstract

We adapted the approach used for the integral assessment of the status of ecosystems in order to assess population status. Classic theoretical concepts of fish population dynamics are the basis of this approach. The convolution of information about changes in several structural and functional characteristics into one integral index was performed using the analytical function of desirability. The index varied 0 to 1 and quantitatively characterizes the state of the population. This approach was tested on the example of the European grayling Thymallus thymallus (Linnaeus, 1758), inhabiting the Vym River (basin of the Northern Dvina River, North of the European part of Russia). The materials were collected during the environmental monitoring carried out by the Institute of Biology of Komi Science Centre of the Ural Branch of the Russian Academy of Sciences (IB FRC Komi SC UB RAS) in 2002, 2005–2019. The population parameters used in the calculations (relative abundance; average and maximum age of fish; the proportion of matured individuals in the 4+ age group; average specific growth rate of fish at the age of 6+; body weight of fish in the age group 6+) were characterized on the basis of the control net catches. Compared with the period 2005–2006, the value of the integral index in 2015–2018 decreased by almost two times. This indicates deterioration in the condition of the grayling group in the study area. There were no serious disturbances in the fish habitat in this area. The main hydrochemical and hydrobiological indicators have not changed significantly. The main reason for the observed changes is likely the significant increase in the impact of recreational anglers. The proposed integral index may be useful both for assessing the state of fish populations and for developing measures for the rational management of fish stocks.