Journal Article

Application of <i>in situ</i> target-strength estimations in lakes: examples from rainbow-smelt surveys in Lakes Erie and Champlain

L.G Rudstam, S.L Parker, D.W Einhouse, L.D Witzel, D.M Warner, J.L Stritzel, D.L Parrish and P.J Sullivan

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 60, issue 3, pages 500-507
Published in print January 2003 | ISSN: 1054-3139
Published online January 2003 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/S1054-3139(03)00046-8
Application of in situ target-strength estimations in lakes: examples from rainbow-smelt surveys in Lakes Erie and Champlain

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Acoustic abundance of fish depends directly on the target strength (TS) of the fish surveyed. We analyzed 70 and 120 kHz acoustic data from two lakes with abundant rainbow-smelt (Osmerus mordax) populations. Using repeated surveys through the summer growing season, we derived a relationship between TS (dB) and fish length L (cm) at 120 kHz (TS = 19.9 log10 L − 67.8). Values for 70 kHz were similar. In situ TS increased with fish density, indicating a bias from accepting multiple targets at high fish densities. Correcting for this bias increased estimates of smelt abundance by up to 18% in Lake Erie and up to 100% in Lake Champlain. Multiple modes in the TS distributions observed for older fish do not reflect different size groups, as the same modes can be observed from measurements from a single fish. Smelt released gas bubbles during the evening ascent, and these bubbles had TS (−60 to −58 dB) within the range of TS observed from the fish. Gas-bubble release occurred mostly during the migration. Conducting surveys after the ascent is completed will decrease bias associated with counting bubbles as fish.

Keywords: bubble production; fish density; hydroacoustics; smelt; target strength

Journal Article.  4462 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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