Journal Article

Potential acoustic discrimination within boreal fish assemblages

Stéphane Gauthier and John K. Horne

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 61, issue 5, pages 836-845
Published in print January 2004 | ISSN: 1054-3139
Published online January 2004 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2004.03.033
Potential acoustic discrimination within boreal fish assemblages

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Differences in the acoustic characteristics of forage fish species in the Gulf of Alaska and the Bering Sea were examined using Kirchhoff ray-mode (KRM) backscatter models. Our goal was to identify species-specific characteristics and metrics that facilitate the discrimination of species using acoustic techniques. Five fish species were analyzed: capelin (Mallotus villosus), Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), and eulachon (Thaleichthys pacificus). Backscatter amplitude differences exist among these species, especially between swimbladdered and non-swimbladdered fish. Echo intensities were variable within and among species. The effect of morphological variability was indexed using the ratio of the Reduced-scattering length (RSL) standard deviation over its mean. Morphological variability was low only at fish length to acoustic wavelength ratios less than eight. Target strength differences between pairs of carrier frequencies (ranging from 12 kHz to 200 kHz) differed among species, and were dependent on fish size and body orientation. Frequency differencing successfully discriminated between fish species but the choice of frequency to maximize target strength differences was not consistent among species pairs. Frequency-dependent, backscatter model predictions facilitate comparison of target strength differences prior to acoustic data collection.

Keywords: Bering Sea; forage fish; Gulf of Alaska; KRM model; species identification; target strength

Journal Article.  5210 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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