© 2005 International Council for the Exploration of the Sea
The target strength of Antarctic krill (Euphausia superba) measured by the split-beam method in a small tank at 70 kHz
Tokyo University of Marine Science and Technology 4-5-7, Konan, Minato, Tokyo 108-8477, Japan
*Correspondence to K. Amakasu: tel: +81 3 5463 0481; fax: +81 3 5463 0518. e-mail: soundproc{at}yahoo.co.jp.
The target strengths (TS) of Antarctic krill (Euphausia superba) were measured at 70 kHz aboard the research and training vessel "Umitaka-maru" of Tokyo University of Marine Science and Technology in February 2003 during a Southern Ocean survey. The systematic variations of TS vs. the incident angle of the ensonified wave, henceforth called TS-patterns, were successfully measured for 12 live Antarctic krill. These measurements were compared with the theoretical TS-patterns predicted by the Distorted-Wave Born Approximation-based deformed-cylinder model (DWBA model). While there was good agreement near the main lobe, the measurements were higher than the model predictions in the side-lobe regions; this is consistent with the observations of others. Several possible causes of this discrepancy such as the bending of abdomen and scattering from pleopods were examined, but no single factor was identified as the cause. Rather, it is likely that the discrepancy is a result of a combination of several factors.
Keywords: Antarctic krill, small tank, split-beam method, target strength
Received 24 May 2004; accepted 12 July 2005.
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