Whales struggle to hear each other. Guess whose fault that is
New research into how baleen whales make low, vibrating sounds is also highlighting the serious dangers these animals face from ocean noise pollution.
These bristle-mouthed animals include some of the world’s most recognizable species, including the blue, humpback and bowhead whales, among others.
“They make sounds of very low frequencies very close to the surface,” said Coen Elemans, study author and professor of bioacoustics at the University of Southern Denmark.
“And that’s exactly where we make boating noise, in exactly the same frequency range and also on the surface.”
Low but not deep
Compared to their toothed cousins like orcas or belugas, baleen whales use a novel method to make these rumbling baritones, essentially taking their vocal organs and rotating them to vibrate against an inner “cushion,” researchers say.
“It makes a Harley-Davidson sound like a child’s toy,” said Tecumseh Fitch, co-author and cognitive biology professor at the University of Vienna.
The study, published in the journal Nature, focuses on low-frequency sounds made by these animals — around the 10 to 30 hertz range. Researchers suggest those sounds can’t be made for prolonged periods of time in deeper parts of the ocean because of the whales’ physiology. Farther down, the air is just too compressed to use their vocal organs effectively.
“In other words, they can’t escape the surface noise created by ships, by human noise, by going way down,” Fitch told CBC News from Sanibel Island, Fla.
“It’d be like if you’re in a very crowded bar and you need to sing to find your mate and everybody else is making all this noise.”
Noise pollution strategies needed
Beyond mating, it’s long been known that ship noise impacts whales — both baleen and toothed — and their ability to orient themselves, locate prey and avoid dangers.
“These animals perceive danger by hearing,” said Hussein Alidina, lead specialist for marine conservation with WWF Canada. “So if that aspect is getting masked or interfered with, then it poses a danger to them.”
His organization recently called out delays to the federal government’s Ocean Noise Strategy, which was supposed to come out in 2021 but has yet to be drafted. Alidina’s hope is that a comprehensive strategy will co-ordinate what he refers to as a “fairly piecemeal and geographically separated” current approach to underwater noise.
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How to make a whale sing
Alidina says it’s important the paper highlights the limitation of whales’ bodies to make these sounds.
But just how researchers figured that out involved what Fitch describes as the “ugly business” of whale research: cutting out vocal organs of dead whales.
“These whales, they beach. They’re dying,” Fitch said. “The whale basically immediately starts to decompose.”
Each of the three whales used for the study had died, but it took more than speed to get the samples on ice.
“We were so lucky,” Elemans recalled about two of the samples in the study — a humpback and sei whale. They were found close by, with cold conditions helping to preserve the tissue from rapid decomposition.
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Fitch described these operations involving “giant cranes and chainsaws” because of the whales’ size — a challenge for him and Elemans, who usually work on the vocal organs of smaller animals.
Their next challenge: figuring out how to recreate noise through dead whale larynxes.
“The principle’s always the same. You need to get a large volume of air. You need to attach it in place of the lungs,” Fitch said. “And then basically use your hands and manipulate it to do what the animal in real life would have done with its muscles.”
With the decomposition clock ticking, Fitch said trial and error eventually lead to an accidental eureka moment. They twisted the organ in such a way that achieved the familiar guttural sound of the whale.
“As soon as you hear those sounds, you know, OK, this is it. This is how this thing is designed to make a sound.”
New technology can help with ocean noise
For its part, Canada’s shipping industry association has been trying to educate international ships on the hazards of ocean noise pollution since 2014.
“Ocean-going ships spend a fraction of their time in Canada or Canadian waters,” said Miako Ushio, director of environmental affairs for the Shipping Federation of Canada. “There’s not necessarily a high level of existing knowledge.”
Beyond education, the only measures currently in place, according to Ushio, are to move ships or slow their speeds to make less noise. 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 newer technology can help, too.
“Really, the biggest thing that industry and governments can do is to facilitate movement toward quieter technologies and quieter ships,” Alidina said.
Ushio added that this could include quieter propellers or new hull coatings.
