Temporary threshold shifts from mid-frequency airborne noise exposures in sealsa)
Colleen Reichmuth1, Jillian M Sills1, Jason Mulsow1
1Institute of Marine Sciences, Long Marine Laboratory, University of California, Santa Cruz 115 McAllister Way Santa Cruz, California 95060, USA.
The Journal of the Acoustical Society of America
|June 30, 2025
Summary
Phocid seals show less temporary threshold shift from airborne noise than expected. Their hearing recovers from noise levels below 85 dB SL and 12 minutes duration.
Area of Science:
- Marine Mammal Bioacoustics
- Auditory Physiology
- Wildlife Acoustics
Background:
- Airborne noise impacts marine mammal hearing.
- Understanding temporary threshold shift (TTS) is crucial for conservation.
- Phocid carnivore hearing sensitivity to airborne noise is not well-documented.
Purpose of the Study:
- To assess residual effects of airborne noise on phocid seal hearing.
- To determine hearing thresholds before and after controlled noise exposure.
- To compare noise susceptibility between northern elephant and harbor seals.
Main Methods:
- Behavioral psychophysics used to obtain hearing thresholds.
- Octave-band white noise exposure (1 or 2.5 kHz) at varying levels (65-125 dB SL) and durations (1.5-50 min).
- Threshold shifts measured at center frequency post-exposure.
Main Results:
- Neither seal showed consistent TTS below 85 dB SL or 12 min duration.
- Equal-energy models did not accurately predict TTS patterns.
- Harbor seals exhibited distinct responses, requiring 24 dB higher levels in a second phase.
Conclusions:
- Phocids appear more resilient to airborne noise-induced hearing loss than otariids.
- Potential mechanisms include meatus closure, reducing sound transmission.
- Findings inform environmental impact assessments for marine noise pollution.
