Characteristics of riprapping underwater noise and its possible impacts on the Yangtze finless porpoise

In order to strengthen the shipping capacity of the Yangtze River, riprapping is frequently conducted as a common way of waterway adjustment activities. To study the riprapping noise and its potential impacts on the Yangtze finless porpoise, the underwater noises by four types of riprapping were collected and their sound pressure levels (SPL) and power spectral densities were analyzed. The results show that the source levels of riprapping noise are greater than 151 dB re 1 μPa with majority energy concentrating in low frequency components (< 20 kHz). Root-mean-square SPL of the frequency range between 20 Hz and 100 kHz are higher than 45 dB re 1 μPa, and the one-third octave SPLs are higher than majority of the hearing threshold of the porpoise, indicating that the riprapping noise can be sensed by the porpoise. Considering the porpoise's vocalization and hearing characteristics, it is concludud that the riprapping noise might degrade the natural habitat of the porpoise, and has greater negative effects on the porpoise in infancy, however, less likely damage the auditory of the porpoise. Finally, mitigation measures are proposed based on the analysis.