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Improved parameterization of Antarctic krill target strength models.
Gareth L Lawson1, Peter H Wiebe, Carin J Ashjian
1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA. glawson@whoi.edu
The Journal of the Acoustical Society of America
|February 4, 2006
Summary
Discrepancies in Antarctic krill target strength predictions were resolved by refining theoretical models. New methods incorporating krill size and in situ orientation improved acoustic scattering predictions, aligning them with empirical data.
Area of Science:
- Marine acoustics
- Biological oceanography
- Fisheries acoustics
Background:
- Theoretical models for Antarctic krill target strength historically showed discrepancies with empirical observations.
- Previous models often used simplified assumptions for krill acoustic properties and orientation.
Purpose of the Study:
- To reconcile discrepancies between theoretical predictions and empirical measurements of Antarctic krill target strength.
- To improve the accuracy of acoustic scattering models for krill by refining key parameters.
Main Methods:
- Modeled acoustic scattering using the distorted-wave Born approximation with krill shape represented as a bent, tapered cylinder.
- Constrained sound speed and density contrasts using length-based regressions.
- Measured in situ krill orientation using a video plankton recorder.
Main Results:
- Krill were observed to orient mostly horizontally in situ, differing from previous assumptions.
- Averaging scattering predictions over measured orientations yielded target strength predictions consistent with in situ measurements for large krill (40-43 mm).
- Model predictions were lower than those from the traditional semi-empirical model for smaller krill.
Conclusions:
- Improved understanding of krill acoustic parameters, particularly length-dependent contrasts and in situ orientation, enhances the accuracy of theoretical scattering models.
- The study provides a more accurate method for estimating krill biomass using acoustic surveys.
- Future acoustic surveys should incorporate these refined parameters for more reliable krill stock assessments.