Study on the linearity of the target strength function between juvenile and adult Japanese anchovy (E. japonicus)

Abstract

In this study, target strengths of 31 Japanese anchovy (E. japanicus) were measured to verify a linear function between small size (juvenile stage) and large size (young & adult stage). The TS measurement was conducted at 200 kHz split-beam echosounder with a tethered method under the live condition. During acoustic measurements, an underwater video camera was used to continuously monitor fish behavior. After dividing into 3 groups (juvenile, young, and adult) with TL, acoustic TS data were analyzed. In the preliminary analysis, acoustic TS value of the young (50 ~ 60 mm) and adult (70 ~ 90 mm) group corresponded very close with the previous least-squared regression function (Kang et al., 2009). However, the TS value of the juvenile group (30 ~ 40 mm) was relatively very low, thus does not placed on the fitting line in the previous TS function. According to the result from the measurement, there is possibility that the traditionally TS function with TL might be needed to propose modified TS function under the different grow phase. As this is preliminary study using a few small anchovy, more TS measurement for small group is needed in the future. From this study, we could be considered a choice not existing TS function but modified TS function, considering acoustic survey for juvenile anchovy in the spawning area will be planed.beam echosounder with a tethered method under the live condition. During acoustic measurements, an underwater video camera was used to continuously monitor fish behavior. After dividing into 3 groups (juvenile, young, and adult) with TL, acoustic TS data were analyzed. In the preliminary analysis, acoustic TS value of the young (50 ~ 60 mm) and adult (70 ~ 90 mm) group corresponded very close with the previous least-squared regression function (Kang et al., 2009). However, the TS value of the juvenile group (30 ~ 40 mm) was relatively very low, thus does not placed on the fitting line in the previous TS function. According to the result