РАСПРЕДЕЛЕНИЕ ЧЕХОНИ В СЕВЕРНОМ КАСПИИ И ФАКТОРЫ, ОПРЕДЕЛЯЮЩИЕ ФОРМИРОВАНИЕ ЕЕ СКОПЛЕНИЙ В ЛЕТНИЙ ПЕРИОД

Abstract

In this article researchers for the first time have made the attempt to study sabre fish distribution ( Pelecus cultratus (Linnaeus, 1758)) in summer season in the Northern Caspian Sea and to define the influence of different abiotic factors (depth, transparency, salinity of water) on formation and density of the sabre fish species. For this purpose there were used materials of trawl surveys carried out in 2006 and during the period from 2013 to 2014. The data obtained showed that in summer in the Northern Caspian Sea sabre fish concentrations were found only in the shallow water. The sabre fish concentrations were observed in two areas: western area attached to the Volga water flow, and eastern area attached to the Ural water flow. The weight and age structure analysis of the sabre fish from these areas showed the presence of two regionally-isolated populations: the Volgian and the Uralian. The Volgian population is a predominant type, because it covers larger water area, and its density index of the sabre fish concentrations is notably higher. As for the Volgian population, researchers analyzed the relation between the depth, transparency, salinity and temperature of water and formation concentration of the sabre fish. Best conditions for the big sabre fish concentrations in summer season in the Northern Caspian Sea were found in the areas with depth of 3.5-4.0 m; water transparency 0.4-0.6 m; temperature 23.0-24.5°С and salinity less than 4.0‰. The areas with homohalin and anahalin types of salinity are preferred by the fish.