Spatiotemporal variation of pulse abundance, sound pressure level, and frequency in Mutsu Bay: Implications for...

Diel, seasonal, and spatial variations and regional differences in the pulse abundance of snapping shrimp have been studied. Pulse abundance and acoustic characteristics are affected by environmental changes and anthropogenic noise; however, little is known about the spatiotemporal variability of the latter. This study examined the temporal pulse variation at a fixed point from spring to summer from 2022 to 2024, and the spatial variation across 44 sites (including scallop farm areas) in Mutsu Bay in August 2024, focusing on acoustic parameters. The pulse rate increased with water temperature and depth, and at night, and tended to be higher inside the scallop farms than outside. The peak-to-peak sound pressure level distribution for each pulse shifted toward higher values in warmer months and at night, and appeared to have minimal spatial differences. The peak frequency of each pulse was distributed mainly 6-10 kHz at night; 11-14 kHz became dominant or increased slightly along with 15-18 kHz during the day, depending on the year. The peak frequency tended to dominate 8-10 kHz at shallower sites, 11-13 kHz at deeper sites, and within both these ranges at intermediate depths (35-40 m). Further investigation is required to understand the underlying mechanisms.