Swimming angle and target strength of larval Japanese anchovy (Engraulis japonicus)

Larval Japanese anchovy

The swimming angle of larval Japanese anchovy (Engraulis japonicus) was measured in a tank, and target strength (TS) was calculated using a theoretical scattering model. The mean swimming angle was 12.8° (s.d. = ± 22.1). Increased speeds of flow led to increased mean swimming angles. The mean swimming angle at flow of 5 cm s^[-1] was higher than those at other speeds. TS values were estimated using a distorted-wave Born approximation model for two cases. Average values were 1-3 cm s^[-1] (Case 1: 11.5° ± 22.1) and 5 cm s^[-1] (Case 2: 16.6° ± 21.7) for cases 1 and 2, respectively. For case 1, TS ranged from -92.0 to -74.7 dB with a mean of -79.4 dB at 120 kHz. For case 2, TS ranged from -92.2 to -75.2 dB with a mean of -79.9 dB. The mean TS in case 2 was lower than that in case 1, with the maximum difference being 1.0 dB at 120 kHz [standard length 22.0 mm]. However, there were no significant differences between the regression lines of cases 1 and 2. Thus, changes in flow speed altered the swimming angle of larval Japanese anchovy, but had little influence on TS.

© 2011 公益社団法人日本水産学会