Journal Article

Characterizing uncertainty in target-strength measurements of a deepwater fish: orange roughy (<i>Hoplostethus atlanticus</i>)

R.J Kloser and J.K Horne

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 60, issue 3, pages 516-523
Published in print January 2003 | ISSN: 1054-3139
Published online January 2003 | e-ISSN: 1095-9289 | DOI:
Characterizing uncertainty in target-strength measurements of a deepwater fish: orange roughy (Hoplostethus atlanticus)

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  • Environmental Science
  • Marine and Estuarine Biology


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The variability of ensemble 38 kHz, target-strength (TS38) estimates for orange roughy (Hoplostethus atlanticus) (4.9 dB, factor of 3.1) in deep water (>600 m) limits the use of echo integration for absolute-biomass estimates. Orange roughy are high in oil content, have a wax-ester swimbladder, and show an active-avoidance response to sampling gear. The interpretations of ensemble, in situ target strengths of orange roughy (range 〈TS38〉=−52.9 to −51.0 dB for standard fish length 〈SL〉 = 35 cm) are lower than previous model and surface-based measurements (〈TS38〉 = −48 dB, SL = 35 cm). In situ TS measurements from individuals on the periphery of dense schools were processed to minimize uncertainties from single-target selection criteria, species composition, and active avoidance. Video and acoustic-tracking data quantified the variability in TS measurements arising from the variability in fish orientation. Multi-frequency acoustics and fish tracking are used to quantify in situ TS variability due to species identification and fish density. The Kirchhoff-ray-mode backscatter model was used to illustrate the sensitivity of species-specific backscatter to assumptions of tilt-angle and material properties (density and sound-speed contrasts). We conclude that a remaining source of uncertainty for in situ TS measurements is the assumption that dispersed targets are representative of the survey population.

Keywords: acoustics; deep water; modelling; orange roughy; target strength

Journal Article.  4845 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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