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Kang, D., Cho, S., Lee, C., Myoung, J-G. and Na, J. 2009. Ex situ target-strength measurements of Japanese anchovy (Engraulis japonicus) in the coastal Northwest Pacific. – ICES Journal of Marine Science, 66: 1219–1224. The Japanese anchovy (Engraulis japonicus) is an important species in regard to the fisheries and ecology of the coastal Northwest Pacific. Measurements of ex situ target strength (TS; dB re 1 m2) were made on live anchovy using 38, 120, and 200 kHz split-beam echosounders. The fish were tethered using small hooks attached to their mouths. During the acoustic measurements, an underwater video camera was used to continuously monitor fish behaviour and tilt-angle (θ). Data for 35 individual anchovy ranging from immature to adult sizes (total lengths LT = 4.8–12.2 cm) were analysed. Least-squares regression fits of TS vs. log(LT) were: TS38 kHz = 20 log(LT) − 65.8 (r2 = 0.82), TS120 kHz = 20 log(LT) − 68.4 (r2 = 0.84), and TS200 kHz = 20 log(LT) − 69.1 (r2 = 0.71). The LT vs. wet weight (W; g) relationship for these fish was W = 0.0036 LT3.204. The mean θ for anchovy swimming freely in a large seawater tank was 9.1° (s.d. = 13.1°). These ex situ measurements of TS, LT, W, and θ can be applied to improve acoustic estimates of Japanese anchovy biomass.

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The integrated backscatter power (IBP) from Cochlodinium polykrikoides was measured every 15 min by a 5-MHz acoustic system during a 5-day cultivation with an irradiation cycle. IBP increased by 0.6 dB in 5 days, but varied by 0.83 dB during the irradiation cycle. The daily increase and diel variation in IBP were postulated to be affected by an increase in cell numbers and a diel variation in cell biovolume or density via photosynthesis, respectively. Cell division/separation might also affect a total variation in IBP. This study suggests that high-frequency acoustics may be a potential tool for investigating phytoplankton cell functions.