New research on how female whales make low, vibrating sounds also highlights the serious dangers these animals pose from ocean noise pollution.
These bristle-mouthed animals include some of the world’s most recognizable species, including blue, humpback, and bowhead whales, among others.
“They emit very low-frequency sounds very close to the surface,” said study author and professor of bioacoustics at the University of Southern Denmark, Coen Elemans.
“And that’s exactly where we’re making the boat sound, exactly in the same frequency range and at the same time on the surface.”
Low but not deep
Compared to their toothed cousins such as orcas or beluga whales, baleen whales use a novel method of making these gurgling baritones, essentially taking their vocal organs and rotating them to vibrate against an internal “cushion,” the researchers say.
“This makes a Harley-Davidson sound like a piece of cake,” said Tecumseh Fitch, co-author and professor of cognitive biology at the University of Vienna.
The study, published in the journal Nature, focuses on the low-frequency sounds these animals make, in the range of 10 to 30 hertz. The researchers suggest that due to the whales’ physiology, these sounds cannot be produced for long periods of time in deeper parts of the ocean. Lower down, the air is too compressed to use the vocal organs effectively.
“In other words, they can’t escape the surface noise created by ships and human noise by going too far down,” Fitch told CBC News from Florida’s Sanibel Island.
“It’s like if you’re in a very crowded bar and you have to sing to find your partner and everyone else is making that noise.”
Noise pollution strategies required
Beyond mating, ship noise has long been known to affect both baleen and toothed whales and their ability to navigate, locate prey, and avoid danger.
“These animals detect danger by hearing,” said Hussein Alidina, WWF Canada’s chief marine conservation specialist. “So if that aspect is being masked or interfered with, then it poses a danger to them.”
His organization recently announced delays in the federal government’s Ocean Noise Strategy, which is expected to be released in 2021 but has not yet been drafted. Alidina’s hope is that a comprehensive strategy will coordinate what he calls the “fairly fragmented and geographically separated” current approach to underwater noise.
How to make a whale sing?
Alidina says it’s important that the paper highlights the limitations of whales’ bodies in making these sounds.
But how the researchers figured it out involved what Fitch described as the “ugly business” of whale research: cutting out the vocal organs of dead whales.
“These whales are washing up on shore. They are dying,” Fitch said. “The whale basically starts to rot right away.”
Each of the three whales used in the study had died, but getting the samples onto the ice required more than speed.
“We were very lucky,” Elemans recalled of two specimens in the study — the humpback whale and the sei whale. They were found nearby, and the cold conditions helped protect the tissue from rapid decomposition.
Fitch described these operations as involving “giant cranes and chainsaws” due to the size of the whales; This was a challenge for him and Elemans, who generally worked on the vocal organs of smaller animals.
The next challenge is to figure out how to recreate the noise through dead whale throats.
“The principle is always the same. You need to take in a large amount of air. You need to replace that with the lungs,” Fitch said. “And then basically use your hands and direct the animal to do what it would do with its muscles in real life.”
New technology could help eliminate ocean noise
The Canadian maritime industry association has been trying to educate international ships about the dangers of ocean noise pollution since 2014.
“Ocean ships spend some of their time in Canada or Canadian waters,” said Miako Ushio, environmental affairs director for the Canadian Maritime Federation. “The knowledge available is not necessarily at a high level.”
Beyond training, the only precautions currently being taken are moving ships or slowing their speed to make less noise, according to Ushio. Such measures have been used to help southern resident killer whales in the Salish Sea off Canada’s west coast.
Both Alidina and Ushio agree that new technologies can also help.
“In fact, the biggest thing industry and governments can do is facilitate the movement towards quieter technologies and quieter ships,” Alidina said.
This could include quieter propellers or new hull fairings, Ushio added.