Temporary threshold shifts in Boris the bottlenose dolphin (Tursiops truncatus), varying noise duration and intensity

There is much concern regarding increasing noise levels in the ocean and how it may affect marine mammals. Early on, there was little information regarding how sound affects marine mammals and no empirical data on the relationship between noise intensity and exposure duration. Working with Boris the bottlenose dolphin, Tursiops truncatus, we explored the effects of octave-band noise, and sonar signals on odontocete hearing and noise-induced temporary hearing threshold shifts (TTS). Sound pressure levels (SPLs) and exposure durations were varied to measure the effects of exposure duration and amplitude. Hearing thresholds were initially measured behaviorally, and later using auditory evoked potentials before and after sound exposure to track TTS and recovery. These efforts showed that threshold shifts were not linear but rather shorter sounds required greater sound exposure levels to induce TTS; a contrast to some early published literature. Further, sound exposure levels of sonar signals required to induce TTS were high, supporting the notion that relatively short sounds must be of relatively high intensity to induce threshold shifts. From these data and this remarkable animal, a novel algorithm was written that predicts the physiological effects of anthropogenic noise if the intensity and duration of exposure are known.