|START||NEW VOL 20||SEARCH||STATISTICS||PAS - GDANSK DIVISION|
pp. 109-114, vol. 1, 1997
Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland
Abstract: Schools of fish, aggregations of plankton and concentrations of gas bubbles cause scattering and attenuation 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 frequencies. Diurnal vertical migrations of biological objects (fish and plankton) are easily observed by echosounders. The possible reasons for this well known phenomenon are different: light changes, animal morphology, social behaviour, grazing, chasing 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 accordance with bioacoustic practice, the term zooplankton in this paper will be used for both zooplankton and micronekton.
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© Polish Acoustical Society - Gdansk Department, Polish Academy of Sciences. This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported. (CC BY-NC-SA 3.0)