International Symposium on HYDROACOUSTICS AND ULTRASONICS EAA Symposium (formerly 13 th FASE Symposium) ANAL YSIS OF DIURNAL VARIABILITY OF THE BAL TIC SOUND SCATTERING LAYERS

Gdańsk -Jurata, Joanna Szczucka
unpublished
Schools of fish, aggregations of plankton and concentrations of gas bubbles cause seattering and attermarion of sound waves. In the Baltic Sea, in some seasons and during some hours, at the thermo-and halocline depth there persist aggregations of small marine organisms registered in the range of lower ultrasound frequeneies. Diurnal vertical migrations of biological objeets (fish and plankton) are easily observed by echosounders. The possible reasons for this well known phenomenon are
more » ... menon are different: light changes, animai morphology, soeial behaviour, grazing, ehasing for prey or escaping from predator. The present study aims to recognize diel and seasonal changeability of the zooplankton aggregations, to show some examples of vertical migration and to search for possible mechanisms of large differences between day and night measures of the total backscattered energy, integrated over the entire water column. In aceordanee with bioaeoustic practice, the term zooplankton in this paper will be used for both zooplankton and ruieronekton [2].
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