The ichthyofauna of the Northern Caspian Sea with the deltas of the Volga and Ural rivers is represented by fish belonging to different groups - marine, migratory, semi-anadromous, and river fish [4]. Semi-anadromous fish living most of their life cycle in the desalinated areas of the Northern Caspian migrate to rivers at short distances from estuaries for spawning.
This division is conditional; usually, this group includes roach Rutilus rutilus casspicus (J.), bream Abramis brama orientalis (B.), asp Aspius aspius (L.), carp Surpinus carpio (L.), and zander Stizostedion lucioperca (L.). Some authors add to this list kutum Rutilus frisii kutum (K.) [2; 4], blue beam Abramis ballerus (L.), white-eyed bream Abramis sapa (P.), zanthe Vimba vimba perca (Pallas, 1811), sabrefish Pelecus cultratus (L.), and sheatfish Silurus glanis (L.) [2; 6]. It is noted that some of the semi-anadromous fish also have aquatic herds in rivers [4; 6].
In the delta of the Ural River and the adjacent eastern part of the Northern Caspian Sea, the population of carp is represented mainly by the river, the watercourse form, so in this paper, we refer to roach, bream, asp, and zander, which are the main targets of commercial fishing in the shallow water area, as semi-anadromous fishes. At the same time, the numbers and catches of these fish change significantly from year to year under the influence of natural and especially anthropogenic factors that have intensified in recent years [5; 7; 9]. In this connection, regular studies of the state of populations become important.
The purpose of this paper was to investigate the current state of semianadromous fish populations in the North-Eastern Caspian Sea (NCS).
Studies were conducted on a standard network of stations in the spring, summer, and fall periods of 2016, 2018, and 2020 on the research vessels of Kazecoproject LLP - Altai and Zaisan. During the summer period, we used a 9 m bottom trawl (trawl speed 2.5 knots, duration 30 minutes), and during the spring and fall periods, we used a 4.5 m trawl (trawl duration 20 minutes). During the night period (for at least 10 hours), the order of fixed nets with a mesh size of 20 to 100 mm was exposed. The length of an individual net - 25 m, the height of the wall in the hanging - 2.5-3 m.