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Delphinid behavioral responses to incidental mid-frequency active sonar.
E Elizabeth Henderson1, Michael H Smith2, Martin Gassmann1
1Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093.
The Journal of the Acoustical Society of America
|October 18, 2014
Summary
Delphinids (dolphins) showed behavioral changes during mid-frequency active (MFA) sonar use, but many also changed behavior without sonar. Responses occurred at 122 dB re: 1 μPa, suggesting potential habituation or sensitization.
Area of Science:
- Marine biology
- Bioacoustics
- Oceanography
Background:
- Marine mammals, particularly delphinids, inhabit areas with increasing anthropogenic noise.
- Mid-frequency active (MFA) sonar is a significant source of underwater noise with potential impacts on marine life.
Purpose of the Study:
- To investigate behavioral responses of delphinids to incidental MFA sonar.
- To determine sound pressure levels associated with observed behavioral changes.
- To explore factors influencing sonar impact, such as behavioral state.
Main Methods:
- Opportunistic observations of delphinid groups in the Southern California Bight (2004-2008).
- Utilized visual focal follows, static hydrophones, and autonomous recorders.
- Calculated sound pressure levels (2-8 kHz) and analyzed behavioral changes.
Main Results:
- 26 of 46 delphinid groups exhibited behavioral responses to MFA sonar incidents.
- Observed responses included changes in behavior, vocalizations, or lack thereof.
- Behavioral responses occurred at mean peak sound pressure levels around 122 dB re: 1 μPa.
- Significant percentages of both exposed and unexposed groups altered behavior, complicating direct attribution.
Conclusions:
- Delphinid responses to MFA sonar are variable and may depend on factors like received sound levels and behavioral state.
- Observed responses at lower received levels suggest potential sensitization, while lack of response may indicate habituation.
- Further research is needed to fully understand the complex interactions between sonar and marine mammal behavior.
