Sonar-induced temporary hearing loss in dolphins.

Area of Science:

• Marine Biology
• Acoustic Oceanography
• Wildlife Physiology

Background:

• Human-produced ocean noise, particularly naval sonar, is a growing concern for marine mammals.
• Recent cetacean mass strandings have been anecdotally linked to sonar, but empirical evidence is lacking.
• Understanding the physiological impacts of sonar on marine mammals is crucial for conservation.

Purpose of the Study:

• To empirically demonstrate how naval mid-frequency sonar could induce physiological and behavioral effects in marine mammals.
• To investigate the dose-response relationship between sonar exposure and auditory effects in bottlenose dolphins.
• To compare the effects of sonar exposure on odontocetes with those observed in terrestrial mammals.

Main Methods:

• Controlled experimental studies exposing a bottlenose dolphin (Tursiops truncatus) to mid-frequency sonar.
• Measurement of auditory thresholds and behavioral responses following sonar exposure.
• Analysis of sound exposure levels and their correlation with induced hearing loss.

Main Results:

• Mid-frequency sonar exposure induced temporary hearing loss in the bottlenose dolphin.
• Mild behavioral alterations were observed concurrently with auditory effects.
• Auditory effects were linked to repeated, intense sonar pings (≥214 dB re: 1 microPa(2) s).
• Data support an energy-based model for predicting noise-induced hearing loss.

Conclusions:

• Naval sonar can induce significant physiological (temporary hearing loss) and behavioral effects in bottlenose dolphins.
• Prolonged, high sound exposure levels are necessary to elicit these effects.
• The impact of sonar on odontocetes shows trends similar to terrestrial mammals, highlighting a need for further research and mitigation strategies.