The intensity of low-frequency noise in the ocean has gone up almost 10-fold since the 1960s, but the researchers led by Scott Veirs of the Beam Reach Marine Science and Sustainability School wanted to see if higher frequencies had gotten noisier too.
In listening to a wide range of frequencies as more than 1,600 ships sailed through their Washington state testing site a total of 3,000 times, the researchers found that the ships did more than emit low rumbles that would disturb massive baleen whales. They also increased noise at medium and high frequencies — including at 20,000 Hz, which is the frequency where orcas hear best.
That's especially unfortunate in the Washington state area, which hosts the only population of orcas categorized as endangered. But the study's findings could apply to any number of toothed whales and dolphins that live near coastal areas, where shallow water gives ship noise a higher impact.
Imagine someone turning on a vacuum cleaner next to you at just the right frequency to drown out your conversation and the noises immediately around you. But since hearing is much more important for whales than it is for humans, it might be more apt to imagine someone turning off the lights and spinning you around a few times. We can't really know what the experience is like for the whales — we're just pretty sure it can't be great, especially when their prey is becoming increasingly rare.
But the study did hint at some good news: Veirs and his colleagues found that most of the added noise came from container ships, while military vessels did a good job of keeping quiet.
“It should be easy to reduce noise pollution,” Veirs told the Guardian. “Military ships are quite a bit quieter and there could be straightforward ways of transferring that technology to the commercial fleet."
And the team has an even simpler suggestion in the meantime: slow down. The researchers estimate that slowing down by one knot — just over one mile per hour — could lower a ship's noise by one decibel. "Decreasing speed by six knots could decrease noise intensity by half," Veirs added.
Noise pollution isn't the only thing that whales (and other marine mammals) have to worry about. Warmer oceans are exposing them to more toxic algae blooms, prey is disappearing, toxic chemicals accumulate in their blubber, and whaling continues in many parts of the world. But each one of these issues makes it harder for whale populations to thrive and harder still for them to bounce back when their numbers are low.