ОБ ОСОБЕННОСТЯХ ЕСТЕСТВЕННОГО ВОСПРОИЗВОДСТВА ЛЕЩА (ABRAMIS BRAMA ORIENTALIS, 1758) НА НЕРЕСТИЛИЩАХ НИЗОВИЙ РЕКИ ВОЛГИ В МНОГОВОДНОМ 2013 И МАЛОВОДНОМ 2015 ГОДАХ

Abstract

The article presents data on spawning sires and feeding the young of bream ( Abramis brama orientalis , 1758) taken in the period from April to July 2013 and 2015 in the spring floods of the Volga delta: in the west - around the Main, Kirovsky and Gandurino banks; in the east - around Vasiljevsky and Belinsky banks. It has been found that all the components of spring flood lay the foundations of a wide range of reasons influencing primarily the efficiency of natural productivity of the species. The article presents data on distribution of bream larvae and juveniles in the eastern and western parts of the Volga delta, in the lower part of the Volga-Akhtuba flood-lands and in the kultuks. The efficiency of natural reproduction of bream depending on changes of hydrological regime has been estimated. More favorable conditions for bream sire reproduction took place in the high-water year of 2013, when the total number of fry on the spawning grounds of the lower part of the Volga-Akhtuba flood-lands and the Volga delta made 3.1 times more than in the low-water year of 2015. In 2013 the highest productivity of bream fry was registered in the eastern spawning grounds in the middle part; in 2015 due to late flooding of spawning grounds and early run of the fry from the spring floods and from the channel banks, the fry number grew in the kultuks. At the end of the flooding the average length of the fry fishes made 11.7 mm, mass - 18.5 mg, which was 2 and 14 times less than in 2013, correspondingly. The main reason of juvenile bream abundance reducing in 2015 was unfavorable hydrological conditions resulting in reduced spawning areas in the Volga delta. Bream fry had no time to grow over a short period of staying in the spring floods and had to run into kultuks of the North Caspian at the unviable stage of development, which lead to negative consequences of survival and productivity of bream species.