Biology and traits of the formation of stock of big-eyed shad Alosa saposchnikowii

Special traits of distribution, reproduction, growth, feeding, and population abundance of the big-eyed shad Alosa saposchnikowii are discussed. In investigations of the formation of abundance, the focus is on the strategy of observations on the stock in the absence of fishery statistics data. The informational representativeness of two monitoring methods is noted: trawl survey of the annual abundance of underyrearlings and census of the relative abundance of spawners recalculated per 100 nets. The big-eyed shad was a secondary commercial species. At present it prospers and occupies a leading position among herrings. In the observed period of sea transgression, in the northern Caspian Sea where principal spawning grounds of herrings are situated, the freshened zone has considerably widened, with conditions favorable to the spawning of big-eyed shad. As a result, its abundance has increased. In spite of the increase in species abundance, its linear and weight growth also increased. The latter is attributed to the change in the diet of the big-eyed shad, namely, its transition to consumption of food consisting mainly of fish.