Acoustic Target Strength of the Pelagic Fish in the Southern Waters of Korea I. In situ Measurement of Target Strength of Anchovy (Engraulis japonica)

The in situ target strength for the anchovy (Engraulis japonica) were measured by the split beam echo sounder system at 38 kHz. This study allowed us to detect the single echos from anchovy shoals which were dispersed during trawling operation in day time. The results of our study were as fellows: We found that the anchouy occupied about of the total catch from the detected shoals from which target strength data were collected. Length distribution of anchovy showed a mode and ranged from 13.6 to 15.4cm with a mean of 14.4cm and a standard deviation of 0.45cm, and weight distribution showed a mode and ranged from 16 to 28 g witha mean of 21.9 g and a standard deviation of 2.7 g. The target strength distribution of anchovy ranged from -40.7 dB to -69.2 dB in the water layer of , -42.19 to -67.7 dB in the and -42.2 to -67.7 dB in , showing 2 modes in each layer, respectively. Overall mean target strengths were -49.7 dB/fish and -33.1 dB/kg, averaged by area backscattering cross section , and the confidence interval for target strength was less than 1 dB. With the mean total length and the mean target strength, we drived the target strength-length relationship as .