BIOLOGICAL CHARACTERISTIC OF THE REPRODUCTIVE GUILD OF ACIPENSER RUTHENUS (LINNAEUS, 1758) IN THE SEVERNAYA DVINA RIVER

Abstract

According to results of ichthyological monitoring of the sterlet population in the middle part of the Severnaya Dvina river in the spring period 2018–2020 established a greater dependence of the value of catches in stationary traps on the dynamics of the water level in the river, compared with water temperature. On the spawn places located in the middle part of the Severnaya Dvina river in the catches of stationary traps, sterlet dominates both in quantity and in mass. Average catch per unit of fishing effort (CPUE) is more dependent on water level dynamics than on water temperature. Age and length composition of sterlet catches is represented by two-thirds by fish of the younger age classes (3–5+) and small sizes (30–45 cm and 0.2–0.6 kg). The sexual structure of spawning sterlet represented by about 80% of males. The sterlet in the Severnaya Dvina river is currently grow faster than 70 years ago – probably due to an increase in the average water temperature in the river. In pre-spawning and spawning parts of sterlet population proportion of maturing and sexually mature females and males is 90%. The number of past-spawners increases with increasing water temperature. Currently, sterlet grows more slowly than in the 50–60s of the 20th century. Sterlet is intensively fed in the Severnaya Dvina river during the spawning period. In the middle part of the river, the basis of spring nutrition is chironomids and caddis fly larvae. Secondary fed objects are bivalve mollusks and blackfly. Random objects characterizing the nutritional spectrum in the spring include larvae of flies, butterflies, hemipterous and fish eggs. There are no significant differences in fed of sterlet with an increase in its size in the Severnaya Dvina river.