Acoustic Characteristic of Sailfin Sandfish (Arctoscopus japonicus) in Dokdo, Republic of Korea

Abstract

The aim of this study is to determine the acoustic characteristics of sailfin sandfish over a wide frequency range. The acoustic survey was conducted in February, May, and August 2015 off Dokdo, Republic of Korea using EK60 echosounder (18, 38, 70, 120, and 200 kHz) with the mid-water trawls. Target strength (TS) of sailfin sandfish as functions of frequency and tilt angle was modeled using the KRM (Kirchhoff-ray mode) backscatter model. The sailfin sandfish characteristics were examined by using the ΔMVBS (difference of mean volume backscattering strength) method and the net opening depth method, respectively. The acoustic signals were clearly concentrated at 20–100 m water depth. The MVBS tended to become lower as the frequency became higher. The MVBS of sailfin sandfish in the net opening depth was higher than that from the ΔMVBS method, yet both characteristics of frequency response were very similar. In comparison with the frequency response of the ΔMVBS method, that of the modeled TS was very similar in February and May. In particular, the sailfin sandfish were concentrated at 30.80 m depth and favored a temperature below 13°C. Lastly the greatest abundance of sailfin sandfish occurred in May. The highest distribution of sailfin sandfish was in the eastern part of Dokdo in February, in the west, northeastern, and southeastern areas in May, and in southeastern region in August.