Hyungbeen Lee

In situ side-aspect target strength of Japanese anchovy (Engraulis japonicus) in northwestern Pacific Ocean

Acoustic side-aspect target strength (TS) of living Japanese anchovy (Engraulis japonicus) was measured at 120kHz during in situ experiments. The data were collected by lowering and horizontally projecting the splitbeam transducer into the anchovy school. For analysis and interpretation of the side-aspect TS data, acoustic theoretical model, based on the fish morphology, and dorsal-aspect TS data were used. Total length of the anchovy ranged from 6.6 to 12.8cm (mean length 9.3cm). The side-aspect TS distributed between 40 and 55dB, has an obvious length dependency. The mean side-aspect TS of the anchovy was 47.8dB, and the TS was about 2dB higher than mean TS generated from dorsal-aspect measurements. With reference to maximum TS, the results of the side-aspect TS were distributed within the range of the theoretical and dorsal-aspect TS. Apparently these tendency indicates that side-aspect TS measured from the study is useful data. These in situ measurements of side-aspect TS can be applied to improve acoustic detection and estimates of the anchovy, and is necessary to measure with a various frequency and length for making enhance data.

Ex situ echo sounder target strengths of ice krill Euphausia crystallorophias

Ice krill is the keystone species in the neritic ecosystem in the Southern Ocean, where it replaces the more oceanic Antarctic krill. It is essential to understand the variation of target strength (TS in dB re 1 m2) with the different body size to accurately estimate ice krill stocks. However, there is comparatively little knowledge of the acoustic backscatter of ice krill. The TS of individual, formalin-preserved, tethered ice krill was measured in a freshwater test tank at 38, 120, and 200 kHz with a calibrated split-beam echo sounder system. Mean TS was obtained from 21 individual ice krill with a broad range of body lengths (L: 13–36 mm). The length (L, mm) to wet weight (W; mg) relationship for ice krill was W=0.001218×103 × L3.53 (R2 =0.96). The mean TS-to-length relationship were TS38 kHz =−177.4+57log10 (L), (R2 = 0.86); TS120 kHz = −129.9+31.56log10 (L), (R2 =0.87); and TS200 kHz =−117.6+24.66log10 (L), (R2 =0.84). Empirical estimates of the relationship between the TS and body length of ice krill were established at 38, 120, and 200 kHz and compared with predictions obtained from both the linear regression model of Greene et al. (1991) and the Stochastic Distorted Wave Born Approximation (SDWBA) model. This result might be applied to improve acoustic detection and density estimation of ice krill in the Southern Ocean. Further comparative studies are needed with in situ target strength including various body lengths of ice krill.

Hydroacoustic Survey of Fish Distribution and Aggregation Characteristics in the Yongdam Reservoir, Korea

국내 내수면은 하천의 수위 유지 및 농업용수 공급을 위한 보 부터 수자원의 효율적인 관리 및 발전소 운영을 위한 다목적 댐 에 이르기까지 다양한 규모의 수리 구조물이 축조되어 있다. 그 중 용담호는 2001년 용담댐이 준공되어 생성된 인공호수로 서 해안 지역의 효율적인 수자원으로 사용되고 있다. 2000년 이전 용담호는 얕은 수심 및 빠른 유속의 계류성 하천이었으나, 용담 댐 완공 이후 완만한 유속 및 정체로 인한 오염 물질의 퇴적 현 상으로 생태계 큰 변화가 진행되고 있는 수역이다(Lee et al., 2009). 특히 용담댐 건설 이후 서식지의 수몰로 인한 고유 어종 의 서식지 감소와 블루길과 배스 등 외래종의 유입으로 생태계 교란이 진행되고 있다(Yang et al., 2012). 국내에서 육상 담수역 및 해양에서 어류의 시·공간적인 분포 파악을 위한 조사는 1960년 이후 현재까지 주로 어구어업으로 진행되고 있다(Choi, 1971; Huh, 1986; Cha et al., 2004). 용담 호 또한 2000년 이후 낚시, 투망, 족대, 일각망 등의 어구 조사 를 통해서 어류의 종조성 및 분포 특성에 대한 연구가 진행되고 있다(Lee et al., 2009; Yang et al., 2012). 이러한 전통적인 채집 방법은 정성적인 자료 측면에서 많은 장점이 있지만, 한정된 채 집 면적 및 수층 제한성이라는 측면에서 정량적인 자료 도출에 오차를 만들어 낼 가능성이 높다. 정성 분석이 치우친 어구 채집 방법의 문제점을 극복하기 위한 방법 중 하나인 생물 음향 기법 은 1980년대 초 제시되어 국내에서는 1990년대 이후 주로 해양 생물의 분포 및 자원량 조사에 활발히 적용되고 있다(Kang et al., 2003; Lee et al., 2014). 생물 음향조사는 국외에서 해양 생태계뿐만 아니라 호수 및 저수지와 같은 담수 환경에서 어류 분포의 정량적인 평가와 대 상 어류의 모니터링 및 생태학에 관한 연구에 적용되고 있다 (Godleska and Jelonek, 2006; Knudsen and Larsson, 2009). 생물 음향 기법의 특징은 연구자의 주관을 배제시키고 사전에 설정된 음향 조사 정선으로부터 연속적이며 전 수층에 대한 객 수중음향기법을 이용한 용담호의 어류 분포특성 연구 이형빈·이경훈*·김성훈·김인옥·강돈혁

The diel vertical migration of the sound-scattering layer in the Yellow Sea Bottom Cold Water of the southeastern Yellow sea: focus on its relationship with a temperature structure

Using the hydroacoustic method with a 200 kHz scientific echo sounding system, the diel vertical migration (DVM) of the sound-scattering layer (SSL) in the Yellow Sea Bottom Cold Water (YSBCW) of the southeastern Yellow Sea was studied in April (spring) and August (summer) of 2010 and 2011. For each survey, 13–27 hours of acoustic data were continuously collected at a stationary station. The acoustic volume scattering strength (Sv) data were analyzed with temperature profile data. In the spring of both 2010 and 2011, the SSL clearly showed the vertical migration throughout the entire water column, moving from the surface layer at night to near the bottom during the day. Conductivity, temperature, and depth data indicated that the entire water column was well mixed with low temperature of about 8°C. However, the SSL showed different patterns in the summers of 2010 and 2011. In the summer of 2010 (≈28°C at the surface), the SSL migrated to near the bottom during the day, but there were two SSLs above and below the thermocline at depth of 10–30 m at night. In the summer of 2011 (≈20°C at the surface), the SSL extended throughout the entire water column at night, possibly owing to an abrupt change in sea weather conditions caused by the passage of a Typhoon Muifa over the study area. It was concluded that the DVM patterns in summer in the YSBCW area may be greatly influenced by a strengthened or weakened thermocline.

Acoustic monitoring using multi-beam imaging sonar through a set net in the Southern Sea, Korea

This study investigated a method for monitoring fish flux though a set net in the coastal South Sea, Korea, using sideward-looking wide angle multi-beam imaging sonar (blueview). This data set was used to examine the impact of changes in diel variation and current speed from a set net. During nighttime, the influx of fish in the set net was significantly 22 times higher than in daytime. The time when high fish flux was observed corresponded to the time of low current speed during nighttime. In contrast, the fish flux was not affecting current speed during daytime. The study provides implications for understanding fish behavior through use of a set net.

Distribution and Abundance of Japanese Anchovy Engraulis japonicus and Other Fishes in Asan Bay, Korea, estimated Hydroacoustic Survey

우리나라 황해 내만 및 연안역은 생물의 다양성이 높은 해역 으로 어류의 산란장 및 보육장으로 이용된다(Kim et al., 1994; Lee and Hwang, 1995). 그 중 아산만은 갯벌이 넓게 발달되어 있어 갑각류와 무척추 동물이 대량으로 서식하여 다양한 연안 어류 및 회유성 어류에 좋은 서식처로 생태계에 매우 중요한 역 할을 담당하는 해역이다(Cha et al., 2013). 하지만 1970년대 이 후 방조제 건설 및 공업 단지의 조성 등의 지속적인 산업화 활 동에 의한 환경 오염의 증가로 해양 생물의 서식처가 위협받고 있는 해역이다(Kim et al., 1994). 또한 아산만 및 남양만 인근 해역은 삽교 및 아산방조제, 서해대교, 남양방조제, 화용방조 제, 석문지구방조제 등의 건설과 석문공단, 인주공단 등 시설 공사로 인한 해양 환경의 변동이 높아 어류의 분포 및 자원량 에 영향을 미칠 가능성이 높은 해역으로 알려져 있다(Lee and Hwang, 1995). 국내에서 해양 및 육상 담수역에서 수산자원의 시·공간 분포 및 자원량 파악을 위한 과학적인 조사는 1960년 이후 현재까지 주로 어구 어업을 이용하였다(Choi, 1971; Huh, 1986; Cha et al., 2004). 어구 조사시 어란 및 유생은 봉고 네트로, 어류 유생 및 성체는 중층 및 저층 트롤과 같은 대형 어구로 채집 후 종조 성 및 체장 특성을 파악하였다. 1990년 이후로는 어류 자원량 추정 모델을 이용하는 간접적인 방법으로 자원량 변동을 추정 하였다(Jang et al., 1992; Choi et al., 1999). 아산만 인근의 어 수산음향기법을 이용한 아산만 멸치(Engraulis japonicus)와 기타어군의 분포 및 현존량 추정 이형빈·강돈혁*·임양재·이경훈

Measurements of Sound Speed and Density Contrasts of the Moon Jellyfish (Aurelia aurita s.l.) for Hydroacoustic Model

Physical properties such as sound speed contrast (h) and density contrast (g) of the interested target are key parameters to understand acoustic characteristics by using theoretical scattering models. The density and sound speed of moon jellyfish (common jellyfish, Aurelia aurita s.l.) were measured. Sound speed contrast (h) was measured from travel time difference (time-of-flight method) of an acoustic signal in a water tank for APOP studies (Acoustic Properties Of zooplankton). Density contrast (g) was measured by the displacement volume and wet weight (dual-density method). The sound speed remained almost constant as the moon jellyfish increased in bell length. The mean values±standard deviation of h and g were 1.0005±0.0012 and 0.9808±0.0195), respectively. These results will provide important input for use in theoretical scattering models for estimating the acoustic target strength of jellyfish.

Acoustic monitoring using bamboo set net in the Southern Sea of Korea

High-temporal resolution profiles of acoustic backscatter were collected from a traditional bamboo set net along the coast of the Southern Sea, Korea, using sideward-looking multi-beam imaging sonar. These data were used to examine the impact of variations in tidal cycles and current speeds on the bamboo set net. The relatively high influx of fish during the nighttime compared to the low influx and high outflux of fish during the daytime suggests visual avoidance of the net by the fish during the daytime. The observed diel variation in the captured fish flux was significantly correlated with the current speed (day: r = 0.35, p = 0.002, night: r = 0.60, p < 0.001). The ratio of influx and outflux of fish, and current speed were correlated in a linear relationship (day: r = 0.45, p < 0.001; night: r = 0.56, p < 0.001). The fish activity of those inhabiting the bamboo set nets appears to be greatly influenced by day-night differences and current speed. The present study enhances understanding of fish behavior via utilization of a bamboo set net in the coastal zone.

Vertical distribution of giant jellyfish, Nemopilema nomurai using acoustics and optics

Nemopilema nomurai jellyfish, which are believed to complete their development in the East China Sea, have started migrating into the Yellow Sea in recent years. We obtained biomass estimates of this species in the Yellow Sea using bottom trawl fishing gear and sighting surveys over a 5-year period. These methods are effective for obtaining N. nomurai jellyfish density estimates and information about the community distribution near the bottom or surface of the sea. To verify the vertical distributions of giant jellyfish between, we used hydroacoustic equipment, including an optical stereo camera system attached to a towed sledge and an echo counting method with scientific echosounder system. Acoustic and optical data were collected while the vessel moved at 3 knots, from which the distribution and density of N. nomurai jellyfish were analyzed. Subsequently, the camera system was towed from a 7 m mean depth to sea level, with the detection range of the acoustic system extending from an 8 m depth to the bottom surface. The optical and acoustic methods indicated the presence of vertical distribution of 0.113 (inds/m3) and 0.064 (inds/m3), respectively. However, the vertical distribution indicated that around 93% of individuals occurred at a depth range of 10–40 m; thus, a 2.4-fold greater density was estimated by acoustic echo counting compared to the optical method.

Analysis on underwater stability of the jellyfish sting protection net installed in the Haeundae beach

The worldwide abundance of various jellyfish appears to have increased in coastal ecosystems in recent years. The enormous jellyfish blooms cause a variety of problems for the local ecology, fisheries, and aquatic-sports in coastal locations. In this study, jellyfish sting protection net was installed to ensure the safety and reduction of the inflow into the Haeundae beach. In order to confirm the stability of the protection net, the tension for protection net was measured from variation of current speed. The periods for maximum tension were observed correspond to the periods of maximum current speed. The maximum tension for protection net was measured up to 4,100 kg. From field evaluations, the jellyfish sting protection net has demonstrated to stability from the current and tide in the Haeundae beach.