Comparison of measurements and model calculations of target strength of juvenile sandeel in Sendai Bay

Abstract

The target strength (TS) of juvenile sandeel (3.1-7.7 cm in standard length, SL) was measured for various tilt angles (-30° to 30°) at 120 kHz, and was compared with the theoretical TS calculated using the theoretical sound scattering model. The maximum TS measured at the tilt angle of 0° ranged from -68.8 to -60.8 dB, whereas the range of the theoretical TS was from - 68.7 to - 61.5 dB. The difference of the measured and theoretical values of the maximum TS was -1.6 to 0.9 dB, and the TS patterns showed good agreement, particularly in the range of the main lobes, in the tilt angle (-10° to 10°). The theoretical model was used to calculate the TS under the same conditions where the specimens were collected. The correlation between the SL and the maximum TS is given by the equation: TS=43.1 log SL - 96.1.