Abstract
In order to observe three species of large jellyfishes Nemopilema nomurai, Rhopilema esculentum and Aurelia aurita s.l. which live in the sea around the Japan, the acoustic camera DIDSON was applied. Effective observation methods using acoustic camera for each species were discussed. Acoustic frequency of 1.1 MHz, 20 m-visibility and vertically downward observation was effective setting for N. nomurai that was distributed in the deep offshore water. Acoustic frequency of 1.8 MHz, 10 m-visibility and vertically downward observation from the sea surface was effective setting for R. esculentum that was distributed in the shallow coastal water. Acoustic frequency of 1.8 MHz, 5 m-visibility and horizontal observation was effective setting for Aurelia that was distributed in the coastal water. Experimental surveys using above settings were carried out by research ships and fishing boat. Individuals of each jellyfish could be visualized clearly on the pictures of the acoustic camera, and data of population density, bell size and swimming direction of each jellyfish were acquired.
