New way to investigate fish density and distribution in the shallowest layers of the open water

• Published in: Fisheries research 2021-06, Vol.238, p.105907, Article 105907
• Main Authors: Baran, Roman, Blabolil, Petr, Čech, Martin, Draštík, Vladislav, Frouzová, Jaroslava, Holubová, Michaela, Jůza, Tomáš, Koliada, Ievgen, Muška, Milan, Peterka, Jiří, Prchalová, Marie, Říha, Milan, Sajdlová, Zuzana, Šmejkal, Marek, Tušer, Michal, Vejřík, Lukáš, Kubečka, Jan
• Format: Article
• Language: English
• Subjects: Echosounder; Hydroacoustics; Lake surface; Sonar; Stock assessment
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/j.fishres.2021.105907

•Quantitative and nondestructive sampling of surface layers of waterbodies represent great challenge.•Investigations show that most of the fish stay in upper meter of the water column barely accessible to traditional acoustic surveying.•Mobile upward looking deployment of echosounder showed distribution of fish similar to Nordic multimesh gillnets.•The upward-looking acoustic system is a promising approach to study the fish community in the neglected surface layer. Information about fish distribution and abundance in the upper part of the water column are often fundamental for both research and management. However, this information is extremely hard to obtain using conventional hydroacoustic methods. For this reason, the mobile hydroacoustic upward-looking system (38 kHz split-beam echosounder) in combination with a passive sampling method (gillnets) was tested to investigate the fish community (fish larger than 8 cm total length) in the upper 3 m of water column of the Římov Reservoir (Czech Republic) during the growing season. We found most fish located in the depth layer closest to the surface down to 1 m – 50–78 % by acoustics (layer 0.3; 1 m) and 55-–1 m) and 55–71 % by gillnets. The size structure of both methods was generally similar, but the acoustic results contained a higher proportion of small fish (