Effects of simulated N-waves on the auditory brainstem response of three species of pinnipeds

Abstract

Pinnipeds (seals and sea lions) on breeding beaches and hauling areas can be exposed to sonic booms from existing and planned civilian supersonic aircraft. Although carpet booms do not produce detectable threshold shifts in humans, the available anatomical information is not adequate to extrapolate models for humans to pinnipeds. Therefore, rehabilitated stranded California sea lions (Zalophus californianus), harbor seals (Phoca vitulina), and elephant seals (Mirounga angustirostris) were exposed to simulated N-waves with levels up to 6 psf and rise times as low as 0.4 ms. The auditory brainstem response (ABR) was used to estimate auditory sensitivity before and after exposure. The test signals were broadband clicks, and tone pips at 2 and 8 kHz. Level of the least detectable ABR waveform was used to estimate best sensitivity, while latencies to the major peaks of the waveform were used to monitor recovery rates. Latency shifts (2 ms) that recovered over the course of a 2-h post-exposure monitoring period were found in some individuals, but these did not correspond to a change in least detectable ABR for any animal. [Work supported by NASA Contract NAS1-20101.]