Bottlenose dolphin temporary threshold shift following exposure to 10-ms impulses centered at 8?kHz

Studies of marine mammal temporary threshold shift (TTS) from impulsive sources have typically produced small TTS magnitudes, likely due to much of the energy in tested sources lying below the subjects' range of best hearing. In this study of dolphin TTS, 10-ms impulses centered at 8 kHz were used with the goal of inducing larger magnitudes of TTS and assessing the time course of hearing recovery. Most impulses had sound pressure levels of 175-180 dB re 1 lPa, while inter-pulse interval (IPI) and total number of impulses were varied. Dolphin TTS increased with increasing cumulative sound exposure level (SEL) and there was no apparent effect of IPI for exposures with equal SEL. The lowest TTS onset was 184 dB re 1 lPa(2)s, although early exposures with 20-s IPI and cumulative SEL of 182-183 dB re 1 lPa(2)s produced respective TTS of 35 and 16 dB in two dolphins. Continued testing with higher SELs up to 191 dB re 1 lPa(2)s in one of those dolphins, however, failed to result in TTS greater than 14 dB. Recovery rates were similar to those from other studies with non-impulsive sources and depended on the magnitude of the initial TTS. https://doi.org/10.1121/10.0020726 (Received 14 March 2023; revised 31 July 2023; accepted 3 August 2023; published online 30 August 2023)

Automated summary

Studies on marine mammal temporary threshold shift (TTS) from impulsive sources have shown small TTS magnitudes, mainly because much of the energy in tested sources lies below the subjects' range of best hearing. In this study of dolphin TTS, 10-ms impulses centered at 8 kHz were used to induce larger TTS magnitudes and assess the time course of hearing recovery.