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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on April 9, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(6):1169-1175; doi:10.1093/icesjms/fsp087
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

This article appears in the following ICES Journal of Marine Science issue: The Ecosystem Approach with Fisheries Acoustics and Complementary Technologies [View the issue table of contents]

Measurements of acoustic-scattering spectra from the whole and parts of Atlantic mackerel

Tonje Lexau Nesse1, Halvor Hobæk1 and Rolf J. Korneliussen2

1 Department of Physics and Technology, University of Bergen, Bergen, Norway
2 Institute of Marine Research, PO Box 1870 Nordnes, N-5817 Bergen, Norway

Correspondence to T. L. Nesse: tel: +47 40825357; fax: +47 55589440; e-mail: tonje.nesse{at}ift.uib.no.

Nesse, T. L., Hobæk, H., and Korneliussen, R. J. 2009. Measurements of acoustic-scattering spectra from the whole and parts of Atlantic mackerel. – ICES Journal of Marine Science, 66: 1169–1175.

Atlantic mackerel (Scomber scombrus) are weak sound scatterers compared with fish that have swimbladders. Accurate acoustic estimates of mackerel abundance require estimates of target strength. Different parts of mackerel may dominate the backscattering spectra. Mackerel schools are acoustically recognized mainly by backscatter four times stronger at 200 kHz than at 38 kHz. Simulations have established that backscatter from only the flesh and the backbone could explain this frequency response, although there are uncertainties in the model parameters and simplifications. In this paper, experiments conducted in a laboratory tank to investigate the complexity of mackerel backscatter are discussed. Acoustic backscatter was measured over the frequency range 65–470 kHz from individual dead mackerel, and their backbones, heads, and skulls. Backscatter from the backbones was measured at several angles of incidence. Grating lobes (Bragg scattering) appeared at different angles, depending on the acoustic frequency and the spacing of the vertebrae. These lobes were evident in backbone backscatter after propagating through the flesh and can be used, in principle, to determine mackerel size acoustically. The frequency response of individual, ex situ Atlantic mackerel estimated from these measurements did not match that from the measurements of in situ mackerel schools. Further investigation is warranted.

Keywords: acoustics, mackerel, multifrequency, relative frequency response

Received 7 August 2008; accepted 14 January 2009; advance access publication 9 April 2009.


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