Sloping migration of young black-backed herring (Alosa kessleri kessleri (Grimm, 1887)) in the lower reaches of the Volga river in 2019

Abstract

In the modern period, the black-backed herring is the only surviving subspecies of the Caspian Sea passing herring. The main factors determining the level of reproduction of black-backed herring in the Volga River are: the number of producers who came to spawn from the sea, the volume of runoff, temperature and hydrological regimes of the Volga River during spawning migrations of producers and the slope of its larvae and juveniles in the sea. Spawning migration of black-backed herring producers from the sea to the river has been observed since the second half of April at a water temperature of 6–8 °C. It has a massive character in May-early June. Reproduction of the black-backed herring begins when the water temperature in the river reaches 16 °C. The descent of its larvae and juveniles in the Volga River takes place during the period of the flood wave recession and the inter-ice period (June, July, August), while the volume of water discharge from the Volgograd hydroelectric power plant, the flow rate and water level in the Volga River affect the conditions of sloping migration, survival and indicators of the number of larvae — a new generation of passing herring-blackback. The highest concentrations of rolling larvae are observed in the last decade of June and the first decade of July. In the modern period , the hydrological regime of the Volga River, the volume and duration of the flood do not provide optimal conditions for the reproduction of black-backed herring, spawning of producers takes place mainly in the middle and lower spawning zones of the Volga River, which leads to a reduction in the migration path of migrating larvae, as a result, they slip at early stages of development with a low probability of survival. Observations of the dynamics of the sloping migration of juveniles allow us to assess the conditions and efficiency of natural reproduction of black-backed herring in the Volga River, the scale of replenishment of stocks of this valuable commercial fish species.