Natural reproduction of commercial fish in the Northern Agrakhan under modern conditions

Abstract

The northern part of the Agrakhan Bay (Northern Agrakhan) has an important fishery importance in the Tersko-Caspian region of the Dagestan River, being a buffer zone where fresh and salt waters mix, therefore it plays a peculiar role of a receiving water body for passable and semipassable fish species migrating to spawning and wintering in the middle and lower reaches of the Terek River. Formation of stocks of commercial fish species in this part of the bay is currently taking place under conditions of reduced efficiency of natural reproduction, which is determined by the conditions of the hydrological and hydrochemical regime. In recent years, anthropogenic factors have caused profound negative changes in the structure of ichthyofauna in the Agrakhan Bay, and the water fishes of the lake-river complex began to dominate and the commercially valuable fish species of passage and semi-passage fish species began to decrease. Studying the dynamics of the number of recorded juveniles of commercial fish species allows not only to assess the efficiency of their reproduction, but also to determine the main causes affecting the reduction or increase in the stocks of various populations. The performed studies allowed to analyze the dynamics of changes in the number of recorded juveniles of commercial fish species that occurred over the last 5 and 10 years. It was confirmed that at present in the bay’s reservoirs low-value fish species are well adapted to the changed unfavorable conditions, as evidenced by the results of reproduction — the number of juvenile silver carp, redfish, perch and gouster increases from year to year. At the same time, against the background of unfavorable hydrological and hydrochemical regime and increased overgrowth of the bay, the migration activity of producers of passable and semipassable species decreases, leading to deterioration of fish reproduction results, which is confirmed by a decrease in the number of recorded juveniles of valuable species: kutum, redfish, vobla, catfish, pike, etc.