Current assessment of factors determining fish reproduction efficiency in the lower reaches of the Ural river

The Aral-Caspian basin plays a crucial role in the formation of commercial fish stocks, which have been de-clining in recent years due to a decrease in the efficiency of natural reproduction due to an unfavorable hydrological regime. The results of studies carried out in 2019-2023 in the lower reaches of the Ural River on the influence of the hydrological regime and the number of producers in spawning areas on the reproduction efficiency are presented using the example of semi-migratory fish: roach, bream, walleye, carp, asp. It is shown that over the past 10 years, low- and medium-water years with a flood flow volume of 2-3 km3 prevailed, and only 3 years were high-water (more than 4 km3). Unfavorable years in terms of water content had a negative impact on the efficiency of fish reproduction in the Ural River, which led to a decrease in the number of offspring and, as a result, a reduction in commercial fish stocks in the region. It was found that in high-water years, even with a low number of producers in spawning grounds, the number of life-resistant sloping juveniles of the studied fish species was greater than in low-water years with a high number of producers. In the course of research, it was found that unfavorable hydrological conditions in the Ural River had a lesser impact on the roach and bream, and the number of juveniles of the latter has increased over the years. Commercially valuable walleye, asp and carp are in a depressed state, the number of recorded juveniles of which was ten times less than bream and roach. The state of reproduction of the carp is alarming, the number of juveniles of which reached a critical level in low-water 2019. According to the results of the study, it is recommended to implement a number of comprehensive measures of fisheries reclamation to improve the state of commercial stocks in the Ural-Caspian region.