현수법을 이용한 보름달물해파리의 예비 음향 특성

Abstract

Jellyfish abundance such as Aurelia aurita and Nemopilema nomurai appears to have seriously increased in recent years in coastal area of Korea, Japan and China. The jellyfish are important consumers of various zooplankton and ichthyoplankton, and may affects fish populations and ecosystem. Thus, knowledge of jellyfish distribution and abundance is of fisheries economic as well as ecological importance. In this study, acoustic target strength (TS) and volume backscattering strength (Sv) measurements for hydroacoustic survey of moon jellyfish are presented for tethered individual and multiple Aurelia aurita in Korean water. Tethered jellyfish were ensonified at 38, 120, and 200 kHz split beam echo-sounders within large cage (6 m  6m  6m). Simultaneously, an underwater video camera was used to continuously monitor behaviour and tilt angle during the acoustic measurements. After TS measurements, density contrast (g) using dual-density method and sound speed contrast (h) using time-of-flight method were measured, respectively. As preliminary results, the acoustic TS of the individual moon jellyfish were various distributed depending on umbrella size; ranging from –67 to –57 dB at 38 kHz, -75 to –57 dB at 120 kHz and –73 to – 57 dB at 200 kHz. The level of Sv was increased as increasing individuals. Experimental results of the acoustic TS and Sv of moon jellyfish distributed intermediate scattering level, which is lower than those of fish and higher than those of zooplankton and ichthyoplankton. Measured results of g (4 individuals) and h (10 individuals) of the moon jellyfish were ranging from 0.9527 ~ 0.9986 and 0.9981 ~ 1.0014, respectively. The preliminary results of ex situ measurements provided various information about the TS of moon jellyfish; this information can be applied to improve acoustic surveys and also improve the accuracy of moon jellyfish biomass estimates.