Since 2005, in the Russian part of the Northern Caspian, Caspian Research Institute of Fisheries has been conducting trawl-acoustic surveys to solve problems in determining the density, biomass and seasonal dynamics of commercial marine fish species. Recently, special attention has been paid to the estimation of the number of sturgeon fishes and their juveniles due to a sharp decrease in the concentrations of these fish in the areas of traditional trawl-acoustic surveys. Until 2015, sonar studies were carried out with the help of a fishfinder echosounder - a video plotter PEV-K, created in the Design Bureau of Marine Electronics “Vector” (Taganrog, Russia). Taking into account the shallow water of the Northern Caspian (depth 3-10 m), this echo sounder of the vertical location gave an insufficiently qualitative quantitative estimate of marine fish concentrations. According to the latest works in the field of acoustics on shallow water bodies, significant shortcomings in the use of vertical echolocation only have been identified, due to a significant underestimation of fish in the near-surface layer in shallow water conditions. It is proved that the most optimal alternative for conducting trawl-acoustic surveys is the simultaneous use of vertical and horizontal echolocation. Solving the actual problems of obtaining representative acoustic data, Caspian Research Institute of Fisheries acquired EY-60 hydroacoustic complex from “Simrad”, using the complex allows simultaneous horizontal and vertical echolocation. Within 2015-2017, with the help of this complex, a survey considering sturgeon yearlings was regularly conducted in the Northern Caspian.
Long-wave sensitivity in the masked greenling (Hexagrammos octogrammus), a shallow-water marine fish
