Species discrimination of fish using frequency-dependent acoustic backscatter

• Published in: ICES Journal of Marine Science
• Main Authors: Logerwell, Elizabeth A., Wilson, Christopher D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2004
• Subjects: Theragra chalcogramma; Alaska
• Online Access: http://dx.doi.org/10.1016/j.icesjms.2004.04.004; http://academic.oup.com/icesjms/article-pdf/61/6/1004/29121875/61-6-1004.pdf

Abstract The difference between mean volume-backscattering strength at 120 and 38 kHz (ΔMVBS) has been used to discriminate acoustically between macrozooplankton species, and between macrozooplankton and fish or small zooplankton. We examined whether ΔMVBS could be used to discriminate between juvenile pollock (Theragra chalcogramma) and capelin (Mallotus villosus). Acoustic data at 38 and 120 kHz were collected in the Gulf of Alaska during August 2000 and 2001. We selected scattering layers of juvenile pollock and capelin that were sampled directly by midwater trawls. Although we found statistically significant differences at minimum integration thresholds ranging from −85 dB to −69 dB, the greatest difference between ΔMVBS of juvenile pollock and capelin was observed at the highest integration threshold (−69 dB). We also found that, although there was substantial overlap between the frequency distributions of juvenile pollock and capelin ΔMVBS at the smallest scale of analysis (0.1 nautical mile × 5 m cells), there was virtually no overlap between the ΔMVBS distributions at the largest scale (∼1 nautical mile × 20 m aggregations). We conclude that acoustic differencing at the scale of fish aggregations and at high integration thresholds can be used to distinguish between juvenile pollock and capelin.