Characteristics Of The Underwater Soundscape In The Yangtze Estuary And Its Adjacent Waters And Its Possible Impact On The Yangtze Finless Porpoise

Underwater environmental noise has long been an important area of study in underwater acoustics and acoustic oceanography and has recently entered the forefront of public awareness.There is a link between human noise and marine mammal ecology,as noise from human activities can harm marine mammals or seriously disrupt their normal life.As the only freshwater cetacean remaining in the Yangtze River Basin of China,the Yangtze finless porpoise is a first-class protected animal in China.The largest estuary in China,the Yangtze Estuary,is one of the main habitats for the Yangtze finless porpoise.In order to gain an in-depth understanding of the characteristics of the underwater soundscape in the Yangtze River Estuary and understand the magnitude of the underwater noise generated by conventional monitoring and survey ships,in December 2021 and November 2022,the noise generated by the Yangtze River Finless Porpoise Monitoring Platform and the survey ship in the Yangtze Estuary were collected respectively.acoustic data.Since the finless porpoise in the Yangtze River estuary is active in the wild,it is difficult to directly observe its behavior.In order to determine whether the underwater noise level of the Yangtze River estuary affects the finless porpoise,it is convenient to compare the experiments in the Hewangmiao finless porpoise reserve.In June 2021,the underwater acoustic data of the finless porpoise holding pens in the Hewangmiao finless porpoise protection area were collected,and the breathing frequency and feeding situation of the finless porpoise in the holding pens were recorded,and a comprehensive analysis was made on whether the finless porpoise could adapt to the temporary cage The underwater environment in the Yangtze Estuary provides a biological basis for analyzing the impact of the underwater soundscape characteristics of the Yangtze Estuary on the finless porpoise.Comparing the data collected at the Yangtze Estuary with the underwater acoustic data of the holding pens in the Hewangmiao finless porpoise reserve,the power spectral density（PSD）of the acoustic signals at each sampling point was analyzed,and the root mean square sound pressure level(SPL_rms),The sound exposure level（SEL）and sound source level（SL）of the ship,etc.,calculate the root mean square（TOL）value of the 1/3 octave band sound pressure level（TOL）of the acoustic data at each point at different frequencies,draw a curve and compare it with the finless porpoise Compared with the hearing threshold curve,it is analyzed whether the finless porpoise can adapt to the underwater environment of the Yangtze River estuary,and whether the underwater noise generated by the survey ship will affect the finless porpoise.The main results are as follows:（1）The SPL_rms at the Yangtze finless porpoise monitoring platform in the Yangtze Estuary ranged from 94.6 to 104.1 d B,while the SPL_rms at the holding pens in Hewangmiao Finless Porpoise Sanctuary was 108.4 d B.The SPL_rms at the monitoring platform was 4.3 to 13.8 d B lower than the underwater noise at the holding pens.This indicates that the Yangtze finless porpoise can adapt to the underwater acoustic environment at the holding pens,so it is inferred that the finless porpoise can adapt to the waters around the monitoring platform.The estimated sound source level of the survey vessel is greater than 151.8 d B.When the dolphins feel the noise from the survey vessel underwater,they will move away from the survey vessel and dive into deep water to avoid it.（2）The maximum SPL_rms at the Yangtze finless porpoise monitoring platform is 94.7 d B at different frequencies,and the underwater noise level at the holding pens in Hewangmiao Finless Porpoise Sanctuary is less than 106.0 d B.The SPL_rms at the monitoring platform is 11.3 d B lower than the underwater noise at the holding pens,and the overall SPL_rms curve decreases gradually with the increase of frequency,which is much lower than the source level of finless porpoise echolocation.Therefore,the echolocation signal of Yangtze finless porpoise will not be affected by the water near the monitoring platform.The estimated sound source level of the survey vessel is 151.8 d B,which is lower than the echolocation sound source level of the finless porpoise,but the high-frequency sound signal of the finless porpoise decays faster in the water,and when the finless porpoise is closer to the survey vessel,it will still have a masking effect on the high-frequency echolocation signal of the finless porpoise.（3）The sound pressure level in the frequency range of 1-15 k Hz was less than 77.6 d B in the waters near the Yangtze finless porpoise monitoring platform in the Yangtze Estuary,which was 3.1d B lower than the maximum underwater noise level of 80.7 d B at the holding pens,so it was inferred that the underwater at the monitoring platform would not affect the communication between the finless porpoises.The low-frequency noise from the survey vessel will not affect adult porpoises,but the low-frequency noise from the survey vessel will affect the communication between mother and offspring.（4）The root-mean-square（RMS）1/3-octave sound pressure level at the Yangtze finless porpoise monitoring platform in the Yangtze Estuary was less than 86.6 d B,which was less than the RMS 1/3-octave sound pressure level at the finless porpoise sanctuary of 43.4 d B.The underwater sound in the waters near the monitoring platform did not cause a temporary hearing threshold shift of the finless porpoise.In open water,the Yangtze finless porpoise can avoid vessels and avoid the underwater noise from vessels,but in restricted waters,temporary hearing threshold shift may occur.This study can provide a reference for evaluating the impact of human activities on freshwater cetaceans and the characteristics of the underwater acoustic environment that the Yangtze finless porpoise can adapt to.