A recent publication by Lucia Di Lorio and Chris Clark reveals a significant difference in Blue Whale call behavior as a consequence of seismic survey noise generated by “sparkers” – an impulse generator which uses an electrical discharge spark to make a “bang.”
Sparkers, like “seismic airguns” create a loud impulse that penetrates into the seafloor. The reflected impulse is then read and analyzed to create a substrate map. These maps reveal variable densities in the substrate which can indicate oil, gas, and mineral deposits.
What is remarkable in this study is that the whale “receive levels” are fairly low with a mean sound exposure level of 114 dB (re: 1 mPa2 s).
Meanwhile the typical proposed “mitigation thresholds” used in environmental impact constraints are usually at a receive level of 185dB which is 70dB higher – equating to 10 million times more energy.
A dominant justification for the 185 dB level is that it equates with the amplitude of the whale’s own vocalization levels.
It seems that as we look deeper into our interactions with marine life we are finding that the response thresholds are often much lower than our assumptions. It is also clear that while the whales may be able to “handle” noises as loud as their own songs, that just like humans they respond to the quality of the noise, not just the volume.