Abstract
A behavioral response paradigm was used to measure underwater hearing thresholds in two bottlenose dolphins (Tursiops truncatus) before and after exposure to intense tones. The fatiguing sounds were 3 kHz, 1 s tones. Hearing thresholds were measured at 3 and 4.5 kHz using a vocal response technique and a modified version of the Method of Free Response. Tests were conducted in a 6 m diam, 1.5 m deep vinyl-walled swimming pool. Ambient noise spectral density levels in the pool were approximately 44 dB re: 1 Pa2/Hz. Postexposure threshold measurements normally began within two minutes of exposure and continued for 1015 min following exposure. A temporary threshold shift (TTS) was defined as a 6 dB or larger increase in threshold compared to the corresponding pre-exposure level. Preliminary results indicate no TTS at 4.5 kHz for either subject at received SPLs of 200 dB re: 1 Pa. These data, as well as the test paradigm, absolute hearing thresholds, and observed behavioral reactions, will be presented and compared to existing TTS data for odontocetes.
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