Review of marine mammal temporary threshold shift (TTS) measurements and their application to damage-risk criteria

Intense anthropogenic underwater sound may adversely effect the hearing and behavior of many marine mammals. Exposure to intense sound may produce an elevated hearing threshold, also known as a threshold shift (TS). If the threshold returns to the pre-exposure level after a period of time, the TS is known as a temporary threshold shift (TTS); if the threshold does not return to the pre-exposure level, the TS is called a permanent threshold shift (PTS). PTS and TTS data were used to establish noise exposure limits in humans and TTS data are often used to help predict the effects of anthropogenic noise on marine mammals in the wild. Previous studies of TTS in marine mammals conducted at SSC San Diego have examined the effects of exposure to single 1 s pure tones and underwater impulsive waveforms. This paper reviews the TTS studies conducted at SSC San Diego over the last 5 years and summarizes the resulting data. The application of these data to the development of damage-risk criteria for marine mammals will also be discussed.