Target-strength Measurements of Sandfish Arctoscopus japonicus

Abstract

The goal of this study was to estimate the target strength (TS) of the sandfish Arctoscopus japonicus using in-situ and ex-situ methods with an echosounder. For the in-situ TS measurement, the survey was conducted by taking hydroacoustic measurements at 38 and 120 kHz and using a coastal gill net, in Goseong, in the northeastern sea of Korea in early December 2009. Ex-situ measurement of TS used live specimens and the tethering method, and was conducted at 120 kHz. The distribution of fork length (FL) was bimodal: 14.6-19.8 cm (n = 241 individuals, mean = 17.0 cm) for males and 16.3-24.5 cm (n = 105 individuals, mean = 19.6 cm) for females. The in-situ TS ranged from -79.8 to -59.1 dB (mean = -74.3 dB for males and -64.1 dB for females) at 38 kHz and -79.9 to -56.2 dB (mean = -74.3 dB for males and -64.1 dB for females) at 120 kHz. The mean TS of females was approximately 10 dB higher than that of males at each dominant frequency. The female ex-situ TS values ranged from 68.5 to -54.6 dB, and those of males was from -67.7 to -59.3 dB. The mean TS value for females was 2.9 dB higher than that of males. These results may be used in echo-integration surveys of sandfish to estimate their abundance and seasonal distribution.