Acoustic target strength with the growth stage of fish: A comparison of juvenile and adult Japanese anchovy (Engraulis japonicus)

Abstract

Japanese anchovy (Engraulis japonicus) is one of the important commercial species around coastal waters of the northwestern Pacific Ocean. For various acoustic surveys on spawning or fishing ground, there is necessary to understand target strength (TS, dB) with growth stage of the fishes. However, little is known about TS information of juvenile fishes. This paper presents measures of TS and models for juvenile Japanese anchovy and describes TS difference between young and adult anchovy. The measurements were conducted at 38, 120 and 200 kHz transducers with live 21 individual anchovy (total length; 3.13 to 9.85 cm). For juvenile stage of the anchovy, the TS models were suggested with frequency, respectively. As a result, the mean TS values of young and adult anchovy are very similar to those of previous TS studies (Kang et al., 2009), whereas those of juvenile anchovy were significantly very low. These results show that it is difficult to apply the acoustic characteristics of the anchovy with growth stages as a TS function, especially juvenile anchovy. From this studies, we might be suggested that suitable Japanese anchovy TS equation according to growth stages must be adopted for data analysis of acoustic surveys on spawn and fishing ground.