Behavioural Responses Of Australian Humpback Whales To Seismic Surveys (BRAHSS)


  • How do the level, context, and directivity of seismic sounds affect marine mammal behavioural reactions?
  • Are behavioural reactions to industry sound “biologically significant” in terms of the PCAD framework?
  • Is ramp-up (soft-start) an effective mitigation measure


Large whales call and hear at the low frequencies produced by airguns. They may be more susceptible to the sound of E & P operations than other marine mammal groups. When this Programme began, no data were available on either the hearing sensitivity or the behavioural responses of large whales to airgun sounds.

The Programme commissioned a study to intentionally expose migrating humpback whales to airguns to compare their behavioural, vocal, and other responses to the exposure conditions they experienced. Two populations are being studied; one never hears airguns and the other hears them yearly. Both populations are being tested for response to ramp-up (soft start), the slow increase in array source level required by regulators. Exposures began with a single gun and will culminate in use of a full commercial airgun array as the sound source in 2014. This project is being funded jointly with the U.S. Bureau of Ocean Energy Management (BOEM), a regulatory entity.

Results to date suggest that social factors (presence of other whales) seem to explain whale swimming directions better than the presence of airguns or boat movements. The depth of dives correlates with water depth more than with the presence of airguns. In response to the first stages of ramp-up, whales tend to slow their swimming and respiration rates until the airguns move away. No fleeing responses or outright avoidance of airguns has been observed. To date only a small airgun array of six guns has been used as the sound source. Whether more guns will cause different responses, and whether the two populations differ in their response to exposure will not be known until a full airgun array is used as the sound source in 2014.

Objectives and methods

  • On the population that does not regularly hear airguns, track migrating whales visually from land, tag and follow whales at sea, and locate all whale calls using a passive acoustic monitoring system. On the population that regularly hears airguns, track migrating whales from boats, tag and follow whales at sea.
  • Collect and store all lines of data with a customized software system.
  • Expose whales by towing airguns of various size and number with a vessel at moves at right angles across the north-south migratory corridor.
  • Include appropriate controls in all exposure experiments and pre-determine the number of trials needed using power analysis.
  • Record swim speed, direction and social interactions visually, dive behaviour with tags, and vocal responses with passive acoustic recorders
  • Use mixed models to identify the exposure and contextual variables most likely to explain the observed responses.


This is the first time wild animals have been intentionally exposed to airguns in a well-designed, multi year scientific study. The biological significance of actual whale responses to seismic, and the validity of soft-start as a mitigation measure will be determined in the second half of this project, 2013-2015.

Links to other research

The research team cooperates with two other major Behavioural Response (BRS) studies presently under way. One is a U.S. Navy funded project on the effects of military sonar on cetaceans in California ( The other, called the SSS project, studies the effect of mid frequency sonar on fish and marine mammals but has no web site. These three BRS studies participate in the DECAF project at the University of St. Andrews ( which is devising new metrics for analyzing the behavioural responses of cetaceans to human sound. About 20 species of cetaceans are involved in these three BRS studies.


  • Sydney University and Defense Science and Technology Organisation (Douglas Cato)
  • University of Queensland (Mike Noad, Rebecca Dunlop)
  • Curtin University (Rob McCauley)