Migrations and resources of sterlet Acipenser ruthenus (Acipenseridae) from the lower reaches of the Volga River

Based on long-term materials, spawning, postspawning, and downstream migrations of the Lower Volga sterlet Acipenser ruthenus were studied. The dates, extent, pattern (two-step and one-step) and main parameters of the spawning and postspawning migrations of the previously separated three populations of the Lower Volga starlet—Volgograd and eastern and western delta ones were established. The main differences of the downstream migration of this potanadromous species from that of anadromous species of acipenserids were revealed. It was found that, after downstream migration, juveniles of sterlet form a continuous chain of aggregations from the dam of the Volgograd Hydraulic Power System to the Caspian Sea. Each link of this chain acts as a center of formation of local groups of sterlet that are components of the distinguished populations. It is shown that the observed distribution of sterlet in the lower reaches of the Volga is determined by the location of the spawning grounds of individual populations and the extent of downstream migrations of prolarvae and larvae. The total extent of migrations of sterlet is small (it does not exceed 250 km), which is a cause of the relative isolation of the previously distinguished populations. The stocks of Volgograd sterlet are exhausted at the present time; the recovery of its stock is possible, first of all, at the expense of a decrease in illegal fishing. The resources of the eastern and western delta populations of sterlet are in a satisfactory condition.