Journal Article

Comparing the modelled and measured target-strength variability of walleye pollock, <i>Theragra chalcogramma</i>

Elliott L. Hazen and John K. Horne

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 61, issue 3, pages 363-377
Published in print January 2004 | ISSN: 1054-3139
Published online January 2004 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2004.01.005
Comparing the modelled and measured target-strength variability of walleye pollock, Theragra chalcogramma

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Many biological and physical factors potentially affect target strength. While these sources have been identified, few studies have compared the relative effects of individual factors. Modelled and measured target strengths in non-dimensional metrics were used to compare and rank the effects of fish length, tilt, depth, and acoustic frequency on backscatter intensity. Ex situ measurements of target strength were used to examine the effects of tilt and depth and then compared to backscatter model predictions. Swimbladder volume reduction due to increasing pressure at depth was modelled using Boyle's law and by varying the ratio of dorsal to lateral compression. We found that length has the largest effect on the modelled and measured backscatter intensity, followed by tilt, frequency, and depth. Including tilt distributions in backscatter estimates improved the match between empirical target-strength measures and model predictions. Non-dimensional influence ratios provide insight into the sources and magnitudes of the backscatter variability.

Keywords: acoustics; backscatter; Boyle's law; depth; ex situ measurements; fish behaviour; frequency; model; swimbladder; target strength; tilt

Journal Article.  5859 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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