Abstract:

Studies to determine the presence or absence of temporary shifts in masked hearing thresholds (TTS) in response to 1-s tones of 141--201 dB re: 1 (mu)Pa (S1 tones) were done at 3, 10, 20, and 75 kHz with four bottlenose dolphins and two white whales. Dolphins exhibited short-term changes in behavior above the following levels of S1 tones: 186 dB at 3 kHz, 180 dB at 10 kHz, 181 dB at 20 kHz, and 178 dB at 75 kHz. TTS levels were 194--201 dB at 3 kHz (two animals), 192--196 dB at 10 kHz (two animals), 193--196 dB at 20 kHz (two animals), and 192-194 dB at 75 kHz (two animals). One white whale exhibited no TTS at the highest level at 3 kHz while the other shifted at 198 dB. At 10 kHz the whales were in the upper range of the dolphins. The studies were completed without any harm to animal health or change in day to day behavior. [Work supported by the Office of Naval Research.]