We tend to think of the air-water interface as a barrier to noise. Planes fly over the ocean all the time, but conventional wisdom tells us that most of the sound bounces off the surface of the ocean, and has little impact on the whales and dolphins that swim beneath the surface. A classic paper from 1972 tells us we only need to worry about airplane noise in a narrow cone under the flight path.
We recently worked with colleagues from Curtin University, Udayana University, and Conservation International Indonesia to measure noise levels from commercial jets taking off from coastal runways in Bali and Australia. We found that under certain conditions, those jets introduce up to 130 dB of noise into shallow waters. Those noise levels are high enough to cause disturbance to killer whales.
Planes fly pretty quickly of course, so any noise exposure is fleeting. But during the busiest periods, we recorded planes taking off every 3 minutes! Below is a map of runways, with coastal runways (<10 m above sea level) in red.
We conducted this study during Nyepi, the Balinese Day of Silence. We did not expect to be able to hear airplane noise over background conditions, but we got lucky. Did you know that fish have a chorus of song, just like the dawn chorus of songbirds? Check out the sounds of fish singing below:
And this is the sound of a small boat passing by our hydrophone. In the last few seconds, you can hear the roar of a jet aircraft taking off from the nearby runway of Denpasar airport, Bali, Indonesia.