Methods and results of in situ target-strength measurements of Atlantic cod (Gadus morhua) during combined trawl-acoustic surveys

• Published in: ICES Journal of Marine Science
• Main Author: Ermolchev, Viacheslav A.
• Format: Text
• Language: English
• Published: Oxford University Press 2009
• Subjects: Articles; Barents Sea; atlantic cod; Gadus morhua
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/66/6/1225; https://doi.org/10.1093/icesjms/fsp024

<qd> Ermolchev, V. A., 2009. Methods and results of in situ target-strength measurements of Atlantic cod ( Gadus morhua ) during combined trawl-acoustic surveys. – ICES Journal of Marine Science, 66: 1225–1232. </qd>This paper presents methods for collecting acoustic and biological data, including in situ target-strength (TS) estimates of fish, with results presented for Atlantic cod ( Gadus morhua ) obtained from combined trawl-acoustic surveys. These include fish in the small, average, and maximum length classes, within the range 5–136 cm (total fish length, L T ). The investigations were done using Simrad EK500/EK60 echosounders with split-beam transducers and special post-processing software. Based on an analysis of data collected in the Barents Sea during 1998–2007, a relationship TS = 25.2 log 10 ( L T ) − 74.8 was obtained for Atlantic cod at 38 kHz, with TS in dB and L T in centimetres. Seasonally, and for depths between 50 and 500 m, the variability in cod TS was 3.1 dB, decreasing with depth. The largest day–night difference in mean TS was in August–September, with changes as large as 1.0–1.7 dB. In the other seasons, the day–night difference was <1.0 dB.