Journal Article

Behavioural and physical effect on acoustic measurements of Baltic fish within a diel cycle

A. Orlowski

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 58, issue 6, pages 1174-1183
Published in print January 2001 | ISSN: 1054-3139
Published online January 2001 | e-ISSN: 1095-9289 | DOI: https://dx.doi.org/10.1006/jmsc.2001.1117
Behavioural and physical effect on acoustic measurements of Baltic fish within a diel cycle

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The diel cycle strongly affects fish behaviour and through its vertical migrations causes significant changes in the physical parameters of fish environment and physiology. There is evidence of the influence of these factors on acoustic fish-back-scattering cross-section values. This variability may be considered potentially as one of most important sources of bias in fisheries acoustics. The methods used and the results of analysing the acoustic, hydrographic, and biological data, collected continuously throughout the day at intervals of one nmi, by research vessels of the Polish Sea Fisheries Institute in the southern Baltic in autumns of the years 1989–1999 are described in this paper. Sa values corresponding to the whole water column (equivalent to column-scattering-strength) were calculated for each elementary sampling distance unit (ESDU) and applied for further analysis as a basic acoustic parameter. The mean depth of the fish biomass gravity centre and corresponding values of temperature and salinity at depths of acoustic “gravity centre” were estimated by computer interpolation of hydrological data for all ESDU. On the basis of numeric models of measurements interactions among environmental and behavioural factors and normalised fish acoustic response have been estimated. The significant influence of fish behaviour and physical factors on the effective value of acoustic back-scattering energy was found and has been described and discussed. The results allowed the identification of more characteristic periods of the fish diel cycle that need further research on fish target strength. Models of the basic components of the fish diel cycle can also be applied for wider ecological studies.

Keywords: diel cycle; fish behaviour; acoustic measurements; Baltic fish; physical factors

Journal Article.  0 words. 

Subjects: Environmental Science ; Marine and Estuarine Biology

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