Studies were carried out on the influence of the hydrological and hydrochemical regime on the species diversity and biological parameters of goby fish in the western part of the North Caspian in 2016-2018. It is shown that the species composition in these years was represented by 9 species, with a predominance of sand goby and bighead goby and with the increase in sea salinity, stenohaline fish began to appear: gray whip goby and Khvalyn goby, the number of the latter in catches increased in 2018 compared to 2017 by 16.8 times. The number and biomass of gobies in 2018 increased by 4 times compared to previous years and amounted to 2384 million copies, 16.807 thousand. t., respectively, as well as the improvement of their biological parameters, indicate the favorable state of the population, and hence the food supply for anadromous fish, in particular, sturgeon, semi-anadromous species, marine migratory herring.
The article presents annual statistical data of the Caspian Research Institute of Fishery. There has been kept track of the long term dynamics of the stocks of three species of Caspian sprat (anchovy, big-eyed kilka, sprat) and investigated a process of substituting a food item of sprats Eurytemora grimmi to a small-celled copepod species Acartia tonsa Dana. According to the research results, there has been determined growth potential of stocks of each species. Ctenophoran-Mnemiopsis has an adverse effect on sprat population by eating fish eggs and larvae. Ctenophoram - Mnemiopsis is a nutritional competitor to the full-grown fishes. The article gives recommendations on reclamation of stocks of the most perspective species - common sprat, whose biological characteristics helped not to suffer during Ctenophoram outburst and to increase its population during change of the main food item. Hydroacoustic survey data prove the intensive growth of common sprat biomass in the north-west part of the Middle Caspian. According to the results of the research it may be concluded that to realize the volumes of recommended sprat catch it is necessary to organize the marine fishery of common sprat at the Russian Middle Caspian shelf.
The purpose of the work is to study the possibility of organizing a new type of Caspian Sea sprat fishing in the western part of the Middle Caspian Sea using multi–depth trawls.The method is the performance in 2009–2012 of all-season expeditionary search trawl-acoustic, ichthyological and hydrological works using generally accepted methods.The novelty consists in the conducted studies allowed to assess the distribution and formation of commercial clusters of Caspian Sea sprat in the pre-winter and winter period in the western part of the Middle Caspian Sea. We revealed that in the cold season, in conditions of the lowest water temperature values, specific changes in the behavior of Caspian Sea sprat occur here, which make it possible to effectively catch its accumulations with a multi-depth trawl.The results are based on the analysis of research materials from 2009–2012 that allowed to develop a biological justification for the organization of a new type of marine fishing in the Caspian Sea — the extraction of Caspian Sea sprat by multi-depth trawls.The practical significance — based on the recommendations of CaspNIRKH in 2019, a Russian trawl fishery for Caspian Sea sprat was organized in the western part of the Middle Caspian Sea, which is currently developing successfully.
Since Caspian sprat today is a reserve fishery object, hydroacoustic studies are the main purpose of solving the problem of estimating concentrations, areas and terms of the organization of the Russian marine fishery. A promising fishing area is the region of the middle part of the Caspian Sea, off the Dagestan coast, which has been studied since 2011. As it was found during previous studies, the densest sprat schools form in the autumn period in the bottom layer. The present research focuses on Caspian sprat distribution in the western part of the Middle Caspian in November 2018. Hydroacoustic tacks covered a water area of 630 NM. The echo recordings of hydroacoustic surveys covering the water area at the depths 20-60 m were analyzed. The recordings were studied considering the response of sprat to the day and night light. Processing of hydroacoustic data was carried out in several stages: analytical viewing of echograms purposed to identify specific features of sprat; recording minimum and maximum values of echo intensity depending on the depth; data post-processing in SIMRAD BI-60 program. The distribution of Caspian sprats is represented totally from the water surface to the ground, and layer by layer, in layers of 10 meters from the water surface. It has been stated that in the surface layer there are practically no sprat schools. The maximum value of the average density (8.7 t / mile2) was registered in the bottom layer (40-50 m). The study results can be used in organization of Russian sprats fishing in the Caspian Sea.
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