The Influence of Temperature on the Formation of Caspian Sprat Aggregations During Hydroacoustic Surveys in the Central Caspian Sea in Summer

T. V. Pomogaeva

A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS, Sevastopol, Russia

e-mail: pomogtatyana@mail.ru

Abstract

The paper aims to identify distribution patterns of Caspian sprats (the main commercial fish in the Caspian Sea) in the epipelagic zone of the Central Caspian Sea in summer and to assess the relationship between the fish aggregation density and the temperature gradient, based on hydroacoustic and hydrological data for 2014–2021. Hydroacoustic surveying was carried out in the deep sea (depth up to 800 m) using a Simrad EK-60 hydroacoustic complex installed on R/V Caspian Explorer with stationary split-beam antennas operating at frequencies of 38 and 120 kHz. Biomass was calculated for standard 10-metre layers from 0 to 50 m. The water temperature was measured at depths of 10, 20, 25, 30 and 50 m. The vertical temperature gradient was calculated for the 20–30 m layer. The relationship between the aggregation density and the gradient was assessed using linear regression analysis. It was found that in summer, the bulk of Caspian sprats, migrating for feeding, concentrates in the middle part of the Caspian Sea, in the upper 50-metre layer. From the results of the 2021 summer hydroacoustic survey, a map of the sprat distribution in the middle part of the Caspian Sea was constructed. The maximum concentrations of sprats were observed in the 20–30 m layer. A significant linear relationship (R2 = 0.802) was found between the density of sprat aggregations (over 30 t/mile2) and the vertical temperature gradient (R2 = 0.802) in this layer. It was shown that dense commercial aggregations form at a gradient of no less than 0.3 °C/m and a temperature above 9.0°C at a depth of 30 m. The results can be used to estimate the location of commercial sprat aggregations in the deep-water part of the Central Caspian Sea in summer.

Keywords

Caspian Sea, Central Caspian, Caspian sprat, Clupeonella, hydroacoustic studies, hydroacoustic survey, sounding graph, temperature gradient, water temperature, commercial aggregations

Acknowledgments

The work was carried out as part of the state assignment of A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS on the topic “Study of the biogeochemical patterns of radioecological and chemoecological processes in the ecosystems of the Azov-Black Sea basin water bodies in comparison with other water areas of the World Ocean and individual aquatic ecosystems of their catchment basins to ensure sustainable development in the southern seas of Russia” (no. 124030100127-7). The author is grateful to the management and staff of the Volga-Caspian Branch of the Russian State Research Center of Fisheries and Oceanography (VNIRO) for the material collected during the survey on R/V Caspian Explorer in accordance with clause 78 of the R&D programme using the sea vessels of the Volga-Caspian Branch of the Russian State Research Center of Fisheries and Oceanography (VNIRO) for 2021. “Assessment of the status of sturgeon, mullet and other fish and crayfish stocks in the summer period based on the results of trawl-acoustic and net surveys. Assessment of the ecological conditions of the habitat of water bioresources. Research on the hydrological, hydrochemical, ecological and toxicological characteristics of the habitat and water bioresources, the state of the food base and the abundance of commercial fish species in the Caspian Sea. Assessment of the Mnemiopsis population status”.

About the author

Tatiana V. Pomogaeva, Junior Researcher, A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS (2, Nakhimov Ave., Sevastopol, 299011, Russia), PhD (Agric.), pomogtatyana@mail.ru

For citation

Pomogaeva, T.V., 2026. The Influence of Temperature on the Formation of Caspian Sprat Aggregations During Hydroacoustic Surveys in the Central Caspian Sea in Summer. Ecological Safety of Coastal and Shelf Zones of Sea, (1), pp. 73–84.

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