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pp.235-244
The multi-frequency characteristics of anchovy schools were investigated using six acoustic lines collected at 38 and 120 kHz while a primary trawl survey was conducted from 14 April and 18 April of 2014 in off the coast of Tongyeong and Geo–je. Here, the frequency characteristics mean ΔMVBS that is the difference of Mean Volume Backscattering Strength at two frequencies. To use the characteristics effectively, the optimal cell size (10×2 m) was determined by examining several different cell sizes in consideration with the shapes of fish schools and the ΔMVBS pattern. By examining 6 histograms of ΔMVBS, afternoon groups were occupied more in the ΔMVBS range of –6~–4 dB than that of –4~–2 dB, comparing to morning groups. The ΔMVBS range of the morning groups was between –16.9 dB and 11.6 dB, and that of the afternoon groups –16.7 dB and 13.0 dB. The average and standard deviation were –3.9±3.6 dB in the morning and –4.1±3.4 dB in the afternoon, suggesting that morning groups were 2 dB higher than afternoon groups. The ΔMVBS range of all anchovy schools regardless of morning and afternoon was between –16.9 dB and 13.0 dB, their average ΔMVBS was –4.1±3.5 dB. The characteristics can support to identify anchovy species in the waters where multiple fish species are distributed. It is hoped that this study presents the availability and benefit of acoustic data from a primary trawl survey.
