Eun-A Yoon

In situ acoustic characteristics of the large jellyfish Nemopilema nomurai in the East China Sea

The Nemopilema nomurai is a large jellyfish attaining a weight of 200 kg and bell diameter of 2 m when fully grown. To prevent damage to this species, this study determined the acoustic characteristics of N. nomurai using frequencies 38 and 120 kHz. The CPUE of N. nomurai and the averaged SV of 38 and 120 kHz had a lower (+) correlation coefficient and relationship at 120 kHz (R

Acoustic observation of the behavior of fish in an artificial reef

우리나라는 200 해리 배타적 경제수역 설정 , 연안 해역의 환경오염 , 어민들의 남획 등으로 인하여 연근해 수산자원을 효율적으로 이용하고 관리하기 위하여 생태기반 조성을 위한 인공어초 시설과 직접적인 자원 조성을위해 종묘 방류를 기본으로 하는 바다목장 사업을 적극적으로 수행하여 왔다 . 이와 같이 자연적인 서식지에인공어초를 투하하여 인공적인 서식지를 제공해 줌으로써 변화하는 수산자원의 현존량 평가가 필요하다(Godoy et al ., 2002; Carr and Hixon , 1997; Kang et al .,2011 a; 2011 b; 2011 c). 우리나라에서는 인공어초 설치 효과에 관한 연구가활발히 진행되고 있다 . Lee and Kang (1994), Kim et al .(2010), Yoon et al . (2011), Park et al . (2013) 는어구를 이용하여 인공어초 주변에 서식하는 어종 및현존량을 평가하였고 , Lee (2011; 2013), Oh et al . (2010) 는잠수 및카메라 조사를 통하여 인공어초 내부나 주변에 서식하는어종을 확인하였다 . 뿐만 아니라 Hwang et al . (2004),Kang et al . (2008), Kim et al . (2011), Lee et al . (2012), Lee(2013) 은계량어군탐지기를 이용하여 인공어초 주변에서식하는 어류의 시·공간 분포 및위집 효과에 관한 연구를 수행하였다 . 어구 조사는 어종을 명확하게 파악할수있으나 인공어초와 같은 구조물에 의해 어구 설치에관한 문제점이 발생하고 , 잠수 조사와 수중 CCTV 및카

Behavior and Frequency Analysis of Aurelia aurita by Using in situ Target Strength at a Port in Southwestern Korea

This study was carried out to determine the in situ target strength and behavioral characteristics of moon jellyfish (Aurelia aurita) using two frequencies (38 and 120 kHz) that present a 2- frequency-difference method for distinguishing A. aurita from other marine planktonic organisms. The average TS was shown as -71.9~ -67.9 dB at 38 kHz and -75.5~-66.0 dB at 120 kHz and the average ΔMVBS120-38 kHz was similar at -1.5~3.5 dB. The TS values varied in a range of about 14 dB from -83.3 and -69.0 dB depending on the pulsation of A. aurita. The species moved in a range of -0.1~1.0 m and they mostly moved horizontally with moving speeds of 0.3~0.6 m·s-1. The TS and behavioral characteristics of A. aurita can distinguish the species from others. The acoustic technology can also contribute to understanding the distribution and abundance of the species.

Target-strength Measurements of Sandfish Arctoscopus japonicus

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.

Characterization of Frequency and Aggregation of the Antarctic Krill (Euphausia superba) Using Acoustics

In this study, the dB difference and characteristics of krill swarms inhabiting Subarea 48.1, which includes the west and south of the South Shetland Island and the Elephant Island peripheries, were estimated to distinguish Antarctic krill, using acoustics. From April 13 to 24, 2016, acoustic data were collected along 24 survey lines using the frequencies 38 and 120 kHz, and middle trawling was performed at 7 stations. Using the difference between the dB values of two volume backscattering strength (Sv) frequencies (38 and 120 kHz), a clear acoustic distinction could be made between Antarctic krill (4.9 to 12.0 dB) and fish (−4.0 to −0.2 dB). The distributions and mean Sv of krill swarms in the Elephant Island peripheries and south of South Shetland Island were higher than those in the west of South Shetland Island. The mean length/ height ratio of krill swarms in the west of the South Shetland Island (64.5) was higher than that in the south (35.9) and the Elephant Island peripheries (33.8), with the length of the aggregations exceeding their height. Most krill swarms were distributed between the surface layer (less than 10 m below sea level) and within 200 m of water depth. These results are expected to serve as baseline data for evaluating krill density and biomass by distinguishing them from fish, using acoustics.

Behavioral patterns and in-situ target strength of the hairtail ( Trichiurus lepturus ) via coupling of scientific echosounder and acoustic camera data

The present study focuses on the influence of target strength (TS) changes in the swimming angle of the hairtail (Trichiurus lepturus). We measured in-situ TS at 38 and 120 kHz with luring lamps at a fishing ground for jigging boats near the coastal waters of Jeju-do in Korea. Swimming angle and size of hairtails were measured using an acoustic camera. Results showed that mean preanal length was estimated to be 13.5 cm (SD = 2.7 cm) and mean swimming tilt angle was estimated to be 43.9° (SD = 17.6°). The mean TS values were −35.7 and −41.2 dB at 38 and 120 kHz, respectively. The results will assist in understanding the influence of swimming angle on the TS of hairtails and, thus, improve the accuracy of biomass estimates.

Comparison of Echogram Analysis Methods for Evaluating the Sound-scattering Layer

This study compared the density of fish determined using three different echogram methods: the frequency-difference, time variable, and threshold modification methods. An acoustic survey was conducted off the coast of Jeju Island after sunset. Data at 38 and 120 kHz frequencies were collected using a commercial fishing vessel. As a reference point, the value of that distinguished fish from zooplankton using the 38 and 120 kHz frequencies was set at using the frequency difference, time variable threshold, and threshold modification methods, respectively. The results of this study constitute basic research for estimating fish densities.

The Characteristics and Spatio-temporal Distribution of Fish Schools during Summer in the Marine Ranching Area (MRA) of Yeosu using Acoustic Data

바다목장은 인공어초 주변에 수산자원의 산란 및 서식장으로 제공하여 수산자원을 보존하고 육성 할뿐만 아니라 인위적인 가입을 유도하여 수산자원을 증대시키기 위한 목적을 가지고 있다. 우리나라는 1998년 통영의 어업형 바다목장을 시작으로 하여 2001년 이후 여수의 다도해형 바다목장, 울진의 관광형 바 다목장, 태안의 갯벌형 바다목장, 제주의 체험관광형 바다목장 으로 시범 바다목장을 5개 해역에 조성하였다. 이와 같이 조성 된 바다목장을 효율적으로 이용하기 위해서는 바다목장에 인 공어초를 시설함으로써 나타나는 효과를 지속적으로 평가하여 야 한다. 인공어초 주변에서 서식하는 수산자원의 평가는 어구, 잠수, 수중 카메라, CCTV 카메라, 수중 음향 등의 방법으로 이루어 지고 있으며(Fabi and Sala, 2002; Hwang et al., 2004; Kang et al., 2008; Yoon et al., 2011; Kim et al., 2010; Oh et al., 2010; Kang et al., 2011a; 2011b; 2011c; Kim et al., 2011; Lee, 2011; Lee et al., 2012; Lee, 2013), 이 가운데 어구 조사는 어종을 명 확하게 규명 할 수 있는 장점은 가지고 있으나, 여러 정점을 조 사하기 위해서는 조사 시간이 많이 소요되기 때문에 전체 해역 음향 자료를 이용한 하계 여수 바다목장 해역에서 어군의 시·공간 분포와 특징

An estimation of the sound-speed and density of moon jellyfish (Aurelia aurita) in Korean waters

The sound-speed and density contrasts are important factors in estimating the target strength (TS) of moon jellyfish (Aurelia aurita). In this study, the sound-speed and density contrasts were measured using time-of-flight and neutral buoyancy methods, respectively. The sound-speed contrast of A. aurita was from 0.9966 to 1.0031 (meanSD, ) and no distinct differences in temperature or pulsation activity and weak were found. The density contrast was from 0.9994 to 1.0004 (meanSD, ). The density of A. aurita was substantially different but the density contrast of A. aurita was shown to be similar to that in the sampling location. The results can be used to estimate of TS of A. aurita by acoustic model.