The typical temporal waveforms and spectra of the sounds produced by the three species of snapping shrimp with different claw shapes and almost the same claw lengths were investigated under laboratory conditions. The sound spectra generated by one species of snapping shrimp were also investigated for various claw lengths. For the three species of snapping shrimp, their typical temporal waveforms were similar, but their sound spectra and pulse durations differed. This difference was related to the size of the single cavitation bubble, which was generated by the high-speed water jet emitted from the snapping shrimp claw. The range of difference in the times between the snapping shrimp claw closure and the collapse of the single cavitation bubble for the three species of snapping shrimp seemed to be determined by the difference in the claw shape. The collapse time, the equilibrium radius, and the maximal radius of the cavitation bubble for each species were estimated from the first peak frequency component in the snapping shrimp sound spectrum. For one species of snapping shrimp, the peak frequency components in the sound spectra were observed for various claw lengths and their superposition could be considered as the cause that the broad peak frequency components were variously observed in the averaged snapping shrimp sound spectra, which were measured in many shallow water areas.

The seawater temperature and wind dependences and diurnal variation of the ambient noise at the snapping shrimp colony in shallow water of the southern sea of Korea were investigated. The ambient noise levels are significantly affected by the snapping shrimp sound, when the bottom seawater temperature increases and the wind speed decreases. However, they are not exceptively almost affected by the snapping shrimp sound when the wind speed decreases at low seawater temperatures (<10 °C). In diurnal variation, the ambient noise levels are also significantly affected by the snapping shrimp sound in the morning and night time zones. This study shows that the activity of the snapping shrimp affecting the variation in ambient noise level in shallow water can be related to the wind speed as well as the seawater temperature. This study also shows that the snapping shrimp in diurnal activity can be more active in the morning and night time zones.

The typical temporal waveforms, spectra, and water-temperature dependence of the snapping shrimp sound in the coastal sea of Korea were investigated. The peak-to-peak source levels of the snapping shrimp sound at three sites in the coastal sea, at water depths of 8, 10, and 40 m, were also investigated. The waveform and dominant frequency response band of the sound were similar to those observed under laboratory conditions. The broad peak frequency components of the normalized average snapping shrimp sound spectra measured in nine different coastal sea areas were differently determined by superposition of the peak frequency components of individual snapping shrimp spectra for the each area. The sound did not significantly affect the ambient noise level at a low seawater temperature (<10 °C). The mean peak-to-peak source levels of the snapping shrimp sound at the sites with water depths of 8 and 10 m were similar, with estimated values of 176 ±3 and 175 ±3 dB (re 1 µPa at 1 m), respectively. However, the estimated mean peak-to-peak source level at the site with a water depth of 40 m was 184 ±2 dB (re 1 µPa at 1 m). The differences in the mean peak-to-peak source levels at the three sites could be caused by the differences in the ambient pressure at the sea bottoms of the sites. For water depths below 10 m, the mean peak-to-peak source levels of the snapping shrimp sound were much lower than those estimated in a previous study, in which the water depth at the experimental site was 6.1 m. On the other hand, the mean peak-to-peak source level at the site with a water depth of 40 m was similar to that estimated in a previous study. This study shows that the mean peak-to-peak source levels of the snapping shrimp sound may change as water depth is largely varied.

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In this study, we investigated the effect of the underwater sound channel (USC) on variations in the ambient noise level in the eastern sea of Korea. Hydrophone observations near the USC axis indicated that the ambient noise levels for frequencies <200 Hz were considerably higher than those at other hydrophone depth locations. However, for frequencies >200 Hz, only slight variations in the ambient noise level were detected, regardless of hydrophone depth or distance relative to the USC. The results from this study shows a typical example of the low-frequency ambient noise (<200 Hz) in shallow water being effectively propagated a long distance near the USC axis in the deep ocean along continental slope.