How and why whales sing - and why humans are silencing their songs

WATCH: CGTN's Michael Marillier tries a 'whale song'

They're some of the most incredible sounds on the planet. 

The 'songs' of baleen whales have echoed across the ocean for thousands of years. But scientists have always struggled to explain how they actually 'sing' - at least, until now. 

Researchers released a new report on the structure of the 'whale voicebox' earlier this week. The study explores how whales produce sound while holding their breath. Lead scientist Coen Elemans says they have a unique vocal cord system that allows them to "avoid choking and drowning while vocalizing underwater." 

The baleen group includes iconic species such as the humpback, bowhead, blue and right whale. Elemans and his team believe the whales' vocal cords rub against a cushion of fat and muscle at the back of the larynx. 

This cushion vibrates when the animal breathes out, generating a range of deep, rich calls. This means some species can make sound without having to inhale for minutes at a time. 

"These are among the most spectacular animals," says Elemans. "They have the rare ability to learn new 'songs' and spread their vocal culture across the planet."

The calls are a critical part of the whales' lives. Female humpbacks use them to communicate with their young, while the males 'sing' when trying to attract a mate. Most baleen whales also use sound to find each other in murky water. 

But there is a threat lurking on the ocean surface - the ships that carry goods around the world. 

These vessels usually generate sounds at frequencies between 30 and 300 Hertz (Hz). The study suggests baleen whales struggle to reach levels above 300 Hz. As Elemans explains, they "cannot easily sing higher to avoid human noise."

They also find it difficult to 'sing' below a depth of 100 meters. All this means they have to compete with the roar of ships passing above. 

"The baleen whales are constrained," says Elemans.

Scientists published a metastudy on ocean noise pollution three years ago. Lead author Carlos Duarte said that man-made noise was "a chronic problem that certainly weakens the animals all the way from individuals to populations." 

Duarte said the shipping and drilling industries could cut the amount of human noise by half. He said ship makers should invest in quieter propellers and hulls, while drilling operators should use techniques that limit the amount of underwater vibrations.   

The latest study may help solve the mystery of how whales 'sing' to each other. But it also poses a crucial question: when will humans stop shouting over them?

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