Comparison of sound energy levels of humpback breaching and seismic source
The sound levels of breaching whales can be found in published literature. In a paper published by APPEA, and based on published information, we can see on page 4 that the sound level of a breaching whale is quoted as 200dB re 1 micro Pascal at one metre from the source (ie extremely close to the whale itself!). In the same APPEA publication the sound of a seismic acoustic source is quoted as 230-255dB re 1 micro Pascal at one metre. The sound level obviously depends on the size of the source so, if we take a mid-range source (242dB) we can calculate that the sound of a seismic array at 128m is the same as a whale breaching at 1m. NB. This attenuation is calculated using the physical principles of sound attenuation in water! Thus, it’s little wonder that humpbacks are often seen well within the 500m shut-down zone (and certainly within the 2000m power-down zone) contained in EPBC Act Policy Statement 2.1.
We are fortunate to have available to us, courtesy of Associate Professor Rob McCauley of Curtin University Centre for Marine Science and Technology, the sound of a breaching humpback off the NW Shelf of Australia compared to the sound of a seismic array:
Of course, even though these sounds are the same intensity, many people will note the very large difference in distance. That is 100m versus 6800m, a difference of 6700m. However, bearing in mind the very rapid attenuation of sound in water in the near-field, using physical principles of sound attenuation in water, it can be demonstrated that the sound intensity of a humpback whale breaching at 1m is the same as this 2678 cui seismic array at 68m.
Perhaps that is why personnel on operating seismic vessels often see whales in close proximity to the operation as shown by the following photo of a humpback whale “up close and personal” with an operating seismic array offshore West Africa.
When one considers the facts, surely the conclusions must be different from the claims espoused by eNGOs and the precautionary management measures imposed by most regulators around the world?