Temporary shift in masked hearing thresholds in odontocetes after exposure to single underwater impulses from a seismic watergun

A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and a white whale (Delphinapterus leucas) before and after exposure to single underwater impulsive sounds produced from a seismic watergun. Pre- and postexposure thresholds were compared to determine if a temporary shift in masked hearing thresholds (MTTS), defined as a 6-dB or larger increase in postexposure thresholds, occurred. Hearing thresholds were measured at 0.4, 4, and 30 kHz. MTTSs of 7 and 6 dB were observed in the white whale at 0.4 and 30 kHz, respectively, approximately 2 min following exposure to single impulses with peak pressures of 160 kPa, peak-to-peak pressures of 226 dB re 1 muPa, and total energy fluxes of 186 dB re 1 muPa(2.)s Thresholds returned to within 2 dB of the preexposure value approximately 4 min after exposure. No MTTS was observed in the dolphin at the highest exposure 2 conditions: 207 kPa peak pressure, 228 dB re 1 muPa peak-to-peak pressure, and 188 dB re 1 muPa(2.)s total energy flux. (C) 2002 Acoustical Society of America.