THE RELATIONSHIP BETWEEN POPULATION DISTRIBUTION AND UNDERWATER NOISE OF YANGTZE FINLESS PORPOISE IN ZHENJIANG PROVINCIAL NATURE RESERVE, JIANGSU PROVINCE

With rapid social and economic development in the Yangtze River basin, human activities such as wading are increasing, leading to a rise in underwater noise pollution. This pollution poses significant threats to the Yangtze finless porpoises, as they rely on acoustic signals for survival. To investigate the relationship between their population distribution and underwater noise, a study was conducted over 3 consecutive periods in 2021 within the Zhenjiang Yangtze River Dolphin Nature Reserve, Jiangsu Province. The findings revealed distinct spatiotemporal variations in the population distribution. Visually, Yangtze finless porpoises were observed 46 times within the reserve, while acoustic towed underwater high-frequency acoustic event recorders captured 33sightings, and fixed underwater high-frequency acoustic event recorders recorded 2253 vocal events. Median root-mean-square sound pressure level (SPL_rms) was calculated at 133.80 dB re 1 μPa, with 90% of SPL_rms ranging from 125.77 to 137.42 dB re 1 μPa. This is notably 11.50 dB higher than the average underwater background noise, with a maximum discrepancy of 31.12 dB, excluding noise from human activities. Spatially, the distribution of Yangtze finless porpoise was most concentrated and underwater noise intensity lowest in the northeast corner of Hechang Island. The study highlights a negative correlation between Yangtze finless porpoise distribution and underwater noise intensity, indicating that lower noise levels are conducive to their survival and habitat. Furthermore, 62% of sites in the reserve exhibited a 24h cumulative sound exposure level (SEL_cumw) surpassing the threshold for temporary hearing threshold shift (TTS) in Yangtze finless porpoise, suggesting potential hearing damage if exposed to high-noise environments for extended periods. Consequently, addressing underwater noise pollution is imperative for their conservation. This study provides essential data for mitigating underwater noise pollution and supports efforts to protect and restore the habitat of Yangtze finless porpoise in the protected area.