Characteristics of Acoustic Scattering according to Pulsation of the Large Jellyfish Nemopilema nomurai

In this study, the distribution of Nemopilema nomurai in the waters of Mijo-myeon, Namhae and Gijang-gun, Busan was analyzed; furthermore, echo counting and echo integration methods were used to compare the distribution density. The acoustic system used in the study was a split beam scientific echosounder operating at 38 and 120 kHz (EK-60, Simrad, Norway). Echo counting and echo integration methods were used to determine the density of N. nomurai distributed in the survey areas. The distribution of N. nomurai by water columns, estimated using an echo counting method, was concentrated at approximately 10 m deep in the waters of Mijo, Namhae and 10–50 m deep in the waters of Gijang, Busan; moreover, the distributed depth varied by the surveyed date and time. It was shown that analyzing the acoustic scattering strength of jellyfish obtained from the echo counting method would be more effective for distributional survey of N. nomurai with two frequency system.

Download Full-text

The acoustic characteristics of three jellyfish species: Nemopilema nomurai, Cyanea nozakii, and Aurelia aurita

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp126 ◽

2009 ◽

Vol 66 (6) ◽

pp. 1233-1237 ◽

Cited By ~ 18

Author(s):

Miyuki Hirose ◽

Tohru Mukai ◽

Doojin Hwang ◽

Kohji Iida

Keyword(s):

Sound Speed ◽

Acoustic Scattering ◽

Aurelia Aurita ◽

Target Strength ◽

Bell Diameter ◽

Nemopilema Nomurai ◽

Acoustic Characteristics ◽

Diameter Range ◽

Jellyfish Species ◽

Density Methods

Abstract Hirose, M., Mukai, T., Hwang, D., and Iida, K. 2009. The acoustic characteristics of three jellyfish species: Nemopilema nomurai, Cyanea nozakii, and Aurelia aurita. – ICES Journal of Marine Science, 66: 1233–1237. Reports about jellyfish damaging nets and reducing fish catches are increasing, and data on the abundance and distribution of various jellyfish species are needed to forecast where and when their blooms will happen. Acoustic techniques can be used to obtain this information if the acoustic characteristics of the targets are known. This is a study of acoustic scattering from three jellyfish species: Nemopilema nomurai (order Rhizostomeae), Cyanea nozakii (Semaeostomeae), and Aurelia aurita (Semaeostomeae). Target strength (TS) at 38, 120, and 200 kHz, specific density, and sound speed were measured with live specimens. Specific densities were measured using the displacement–volume–weight and the dual-density methods. The sound speeds were estimated using the time-of-flight method. The reduced TS (RTS), i.e. the TS normalized by bell area, was smaller for N. nomurai (bell diameter range 19–38 cm) than for C. nozakii (bell diameter range 30–40 cm), and the differences in RTS between the species were 17.8, 12.6, and 5.8 dB at 38, 120, and 200 kHz, respectively. The respective sound-speed contrast h and density contrast g were 1.0008 ± 0.009 (mean ± s.d.) and 1.004 ± 0.015 for N. nomurai; 1.038 and 1.073 for one C. nozakii; and 1.0001 ± 0.025 and 0.989 ± 0.019 for A. aurita.

Download Full-text

Estimates of acoustic target strength for giant jellyfish Nemopilema nomurai Kishinouye in the coastal Northwest Pacific

ICES Journal of Marine Science ◽

10.1093/icesjms/fst182 ◽

2013 ◽

Vol 71 (3) ◽

pp. 597-603 ◽

Cited By ~ 2

Author(s):

Donhyug Kang ◽

Jusam Park ◽

Seom-Kyu Jung ◽

Sungho Cho

Keyword(s):

Acoustic Scattering ◽

Ex Situ ◽

Target Strength ◽

Northwest Pacific ◽

Bell Diameter ◽

Least Squares Regression ◽

Acoustic Measurements ◽

Nemopilema Nomurai ◽

Acoustic Target ◽

Giant Jellyfish

Abstract Acoustic target strength (TS) measurements were made of ex situ giant jellyfish Nemopilema nomurai Kishinouye at 38 and 120 kHz. These TS data may be useful for developing acoustic scattering models, and surveying giant jellyfish distributions and biomasses. Each jellyfish was tethered in seawater using a monofilament line that vertically penetrated its bell's centre. During the acoustic measurements, an underwater video camera was used to continuously monitor the jellyfish's behaviour. Acoustic measurements were made using split-beam transducers. TS measurements were made of 27 individual jellyfish, but data were analysed for 23 specimens (bell diameter in air, Dair = 21–65 cm) at 38 kHz, and 19 specimens (Dair = 21–46 cm) at 120 kHz, respectively. Least-squares regression fits of TS vs. log(Dair) were TS38kHz = 20•log10Dair–82.7 (r = 0.76) and TS120kHz = 20•log10Dair–86.7 (r = 0.79). The mean TS values at 38 and 120 kHz, using the average Dair = 40.3 cm and 35.5 cm, respectively, were −50.6 and −55.7 dB. The reduced TS, a function of the ratio of Dair to wavelength (λ), was RTS(Dair/λ) = −6.1•log10(Dair/λ) –36.1 (r = 0.51). These RTS values decreased with increasing Dair/λ. Symbiotic medusa shrimp (Latreutes anoplonyx Kemp) contributed negligible bias to our TS measurements of giant jellyfish. These ex situ TS measurements may be used in acoustic surveys to estimate the distributions and biomasses of N. nomurai.

Download Full-text