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.

Delta and delta front of the Volga river are the main fishing areas in the Astrakhan region, which provide high fish capacity. At the same time, productiveness of fishing in these areas is extremely unstable because they are effected by numerous environmental factors. The essential factor is changing the level of the Caspian Sea, which is directly related to hydraulicity of the Volga watershed. Sea-level change results in changing the area of shallow water zone and coast line, which strongly impacts on a previous biotope. Besides changing the sea level and the volume of fresh-water flowing, water bio-resources are influenced by the volume of spring flood, terms of the flood beginning and thermal regime in the region. Interference of all these factors impacts on stock forming and on fishing of all fish species caught in this region. But this interference of different fish groups (semi-anadromous, river, non-migratory) is ambiguous, which is related with their biology. The purpose of the research is to define the influence of these factors on fishing one of the most important commercial fish species - sheatfish ( Silurus glanis ). The analysis of the available materials has shown that sheatfish catches in a great degree depend on some abiotic factors. Thus, raising the sea level leads to the decrease of sheatfish catches, and increasing of water mass during the flooding period in the Volga river results in lowering the total catch. Later beginning of the flood period improves the effectiveness of fishing, as well as early warning-up of water.

Fisheries measures is an instrument allowing to regulate fish catch pressing to the aquatic bio-resources stocks. Roach and sheatfish are the species which are exploited in industrial and amateur fisheries of the Volga-Caspian basin (the Astrakhan region). According to the Fishery Regulations, today the minimum allowable length for roach is 17 centimeters, and for sheatfish it is 60 centimeters. According to the results of retrospective analysis of stocks dynamics, commercial catch of roach and cheatfish, experience in changing fisheries measures for roach and sheatfish in the Volga-Caspian basin, changing fisheries measures for these species has been found inexpedient. The current fisheries measures for commercial catch of roach allows to exploit only the reproductive part of the population, minimizing losses of restocking. Also, the work shows that a change of fisheries measures for sheatfish will lead to the decrease of the commercial catch of sheatfish and objects of its ration. In general, it must be stressed that changing fisheries measures will lead to redistribution of roach and sheatfish catches between the main participants (commercial fishers, amateur fishers and poachers), but not in favor of the official fish catching