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Alerting responses of marine mammals

Key Questions

  • Develop alternative sound sources or operating procedures, evaluate or improve existing mitigation measures or develop new mitigation measures that would lessen the risk of acoustic impacts on marine animals.
  • Is ramp-up effective at making animals move away from industry sources? Can other methods be developed that will have this effect?
  • Can artificial alerting sounds be created that will move marine mammals out of airgun safety zones prior to start-up under low visibility conditions?

Summary

Regulators often prohibit airgun startup when marine mammal observers cannot see if airgun safety zones are clear of marine mammals. Such delays in startup increase the cost and decrease the efficiency of offshore seismic operations. Removing the limitation of human visibility could permit startup without delays. Novacek et al. 2004 (Proc. Roy. Soc. Lond. B.271:227-231) found that northern right whales can be reliably moved short distances from a ship by playing underwater “alerting sounds,” low amplitude signals that feature frequency upsweeps. This finding prompted the key question above. The Programme funded one project to try out several kinds of alerting signals.

Six types of sound (sweeps and continuous white noise) were used, and 12 bioacoustic tags were deployed on sperm whales that were feeding on hooked fish near fishing boats. No whales moved away from the alerting signal at a received level of about 100 dB re 1 μPa. Normal dive depths and dive profiles did not change during playback. However, vocal buzzes and creaks that indicate foraging did decrease during playback. Tag failure produced smaller sample sizes than expected.

Objectives and methods

  • devise several types of low source level alerting sounds, including sweeps and white noise
  • play these sounds under water near fishing operations that attract whales
  • deploy bioacoustic tags on whales near fishing operations to measure the received levels of the alerting sounds and of any vocal responses
  • record the behavioural responses of whales during playback

Importance

Animals in this study were actively feeding during exposure and may have ignored sounds they would have avoided in any other context. The failure of this project to move animals away does not invalidate the idea of clearing safety zones using alerting sounds. The study should be repeated on this and other species that are not actively feeding, and possibly with greater source levels.

Links to other research

No similar research is presently being conducted elsewhere.

Institutions/PIs

University of California San Diego (Aaron Thode).

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