ТРОФИЧЕСКИЕ ОСНОВЫ ФОРМИРОВАНИЯ ЗАПАСОВ ХАМСЫ В АЗОВСКОМ МОРЕ

Abstract

Formation of the European anchovy Engraulis encrasicolus (Linnaeus, 1758) stocks in the Azov Sea depends on the development of zooplankton, which is the main food source for this fish species. Under the conditions of the natural flow regime of the rivers (1937-1951) and the 10.6 ‰ salinity of the sea, native zooplankton species ensured a high food supply for the anchovy, which resulted in relatively large anchovy stocks. During the Azov Sea salinization up to 12.8 ‰ that occurred in the late 60-70s of the last century, the zooplankton species composition changed. Predatory scyphoid jellyfish species - Aurelia aurita and Rhizostoma pulmo - underwent drastic increase in abundance, which led to the reduction in the summer biomass of the zooplankton almost by half. During that period, large stocks of the European anchovy developed less often. In the late 1980s, as a result of the introduction of a predatory ctenophore Mnemiopsis leidyi in the Azov Sea, the summer biomass of the zooplankton decreased further by 2-3 orders of magnitude. During the feeding season of the European anchovy, the areas with high zooplankton productivity disappeared, which resulted in the recurring low stocks of this fish species. At the end of the 1990s, a ctenophore Beroe ovata , feeding on the mnemiopsis, appeared in the Azov Sea. Its invasion led the delayed entry of the mnemiopsis into the sea, which, in turn, ensured the development of a sufficient food supply for the anchovy during its pre-spawning period. However, the main feeding season of the anchovy, just as before the arrival of B. ovata , took place under a shortage of the food supply. In the last few years, another increase in salinity to 15.0 ‰ is observed in the Azov Sea. The Black Sea jellyfishes A. aurita and R. pulmo are actively developing once again and, along with M. leidyi , provide even stronger food competition for the anchovy. During these years, only low-productive generations and low stocks of this fish species have been observed.