Study on the jellyfish acoustic scattering in Korea coastal region : major three species (A. aurita, N. nomurai and C. nozakii)

Abstract

A massive jellyfish that appeared in the coastal regions of Korea causes sometimes serious damages to marine ecology, fisheries, and related industry over the last decade. The origin and cause of the massive jellyfish have not yet clearly investigated in the ocean. In order to understand the abundance and distribution of massive jellyfish are needed to know where or when their blooms will happen. Then, the acoustic technique is one of the useful methods to obtain the information if the acoustic characteristics of the targets are known. Major jellyfish species in the coastal water of Korea are known to A. aurita, N. nomurai and C. nozakii. During last 3 years, studies on the characteristics of the acoustic scattering strength, especially target strength (TS), have been intensively conducting for the three jellyfishes. For the measurements, 120, 200 and 420 kHz split-beam transducers were used in the large cage and transducer directions for the experiments were separately down-aspect and side-aspect. The numbers for TS measurement were 39 (diameter 10 - 22 cm in air) for A. aurita, 52 (diameter 12 - 79 cm in air) for N. nomurai, and 20 (diameter 19 - 46 cm in air) for C. nozakii, respectively. Considering symbiotic relationship between jellyfish (N. nomurai and C. nozakii) and small fish, TS of the symbiotic fish was also measured. Finally, physical properties such as sound speed contrast and density contrast were investigated to apply acoustic scattering model in the near future. The results of the TS studies for three jellyfish species can be used as an essential data for the acoustic detection of jellyfish in open ocean or coastal area.