The Underwater Sound Emitted by Fishing Training Ship Nansei-Maru

The measurements were carried out for the purpose of grasping the actual condition of underwater sound emitted from the ship, in order to enable a precise evaluation of fish resources using an echo integrator. The results obtained in this study are as follows: 1. When the Nansei-Maru was drifting, the mean value of sound pressure level was 143dB at a vertical distance of just 10m from the ship's bottom. The numerical values with main engine rotation and with the presence or absence of the generator engine showed no significant differences. 2. When the Nansei-Maru was cruising, values of 150dB-153dB were shown at a horizontal distance of 30m from the ship. Fishes were startled by sound pressure levels of 130dB-150dB; the sound pressure level was calculated to be 130dB at a distance of about 380m from the ship and 140dB at a distance of about 120m. It must be borne in mind that escape behavior may be stimulated in schools of fish at these distances. 3. While drifting, many line spectra with higher harmonics were distinguished from the basic frequency of the main engine and the generator engine rotation. 4. While cruising ahead, at a frequency band of 200Hz or less, the continuous spectrum from the propeller blade rotation and the line spectra which arise from the propeller shaft rotation were distinguished