Prerequisites for the expansion of the range of golden grey mullet Chelon auratus (Risso, 1810) in the conditions of inconstancy of the salt regime of the northern part of the Caspian Sea

Abstract

In the Caspian Sea, as in any natural body of water, the distribution and dynamics of the number of fish, including mullet, is due to the combined influence of environmental factors. In the present period of regression of the sea and changes in the level of runoff of the Volga River, salinity plays an important role in the life cycle of all representatives of the ichthyofauna. The article is devoted to the topical issue of the impact of the salt regime on the spatial and quantitative characteristics of the mullet population. The distribution and its relative abundance in 2016 and 2019 observations are presented. The distribution areas are mapped with a detailed description of the features of the formation of concentrations during two contrasting periods: desalination and salinization of the sea. Analyzing the data of trawl catches, it was found that in 2016, when the powerful Volga runoff led to the expansion of desalination zones, the average catch of mullet was 7 copies/an hour of trawling. It is noteworthy that this indicator has grown to 11 copies/an hour of trawling, during the salinization of the Northern Caspian in low-water 2019 Graphical data confirming the presence of a direct correlation between the relative abundance of mullet and increasing salinity gradients are presented. It is shown that for two years the value of the correlation coefficient was 0.74–0.76. Mullet was caught in areas with salinity from 2 to 17%. It was found that the majority of concentrations (68–74%) were formed in marine waters from 8%. In conclusion, it is concluded that the increase in salinity indicators of the northern part of the Caspian Sea has a positive effect on the expansion of the range of mullet.