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ICES Journal of Marine Science: Journal du Conseil 2004 61(3):363-377; doi:10.1016/j.icesjms.2004.01.005
© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
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Comparing the modelled and measured target-strength variability of walleye pollock, Theragra chalcogramma

Elliott L. Hazen1 and John K. Horne*

University of Washington, School of Aquatic and Fishery Sciences Seattle, WA 98195, USA

*Correspondence to J. K. Horne: tel: +1 206 221 6890; fax: +1 206 221 6939. e-mail: jhorne{at}u.washington.edu; ehazen{at}alumni.duke.edu.

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

Received 22 June 2003; accepted 10 January 2004.

1 E. L. Hazen is presently at Duke University, Nicholas School of the Environment, Durham, NC 27708, USA.


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