Common dolphin whistle responses to experimental mid-frequency sonar

Area of Science:

• Marine Mammal Behavior
• Bioacoustics
• Anthropogenic Ocean Noise

Background:

• Oceanic delphinids frequently encounter intense military sonar in Navy operational zones.
• Measuring sonar's behavioral impact on social, free-ranging dolphins is difficult.
• Baseline vocal behavior data is needed to assess anthropogenic disturbance effects.

Purpose of the Study:

• To investigate the effects of mid-frequency active sonar (MFAS) on dolphin whistle production.
• To analyze behavioral responses using varying temporal windows for acoustic analysis.
• To understand common dolphin (Delphinus delphis) reactions to simulated sonar.

Main Methods:

• Conducted controlled exposure experiments using a network of drifting acoustic buoys.
• Simulated Navy mid-frequency active sonar (MFAS) at 3-4 kHz.
• Analyzed whistle production in short-beaked and long-beaked common dolphins over temporal windows from 5 seconds to 10 minutes.

Main Results:

• Common dolphins exhibited acute, pronounced changes in whistle rate within 5 seconds of MFAS exposure.
• This whistle rate response was sustained across sequential MFAS exposures.
• Detected brief, clearly measurable acoustic responses to MFAS, suggesting limited habituation.

Conclusions:

• Common dolphins display detectable acoustic responses to mid-frequency active sonar.
• Variable temporal analysis windows are crucial for detecting behavioral responses to sonar.
• Future research should establish baseline vocal rates to inform analysis of marine mammal responses to disturbance.