/cloudfront-eu-central-1.images.arcpublishing.com/prisa/PH7553GPABDL5BZOBP775AC5E4.jpg "The song of the whales cannot with the noise of the ships | Science")
About 50 million years ago, the ancestors of whales, the same as those of today’s cows, left the earth’s surface to return to the sea. With them they took their system for producing sound, not very different from the human one. But this does not operate the same way underwater and, what is more basic, opening your mouth to produce it means drowning. In their adaptation to the new environment, some species of cetaceans have sophisticated their phonation to such an extent that it seems to humans that they sing.
Now, a group of scientists has dissected specimens of three of them to reveal the secrets of their song. Throughout evolution they redesigned their larynx to continue communicating over very long distances. But their study also shows how human-generated noise is short-circuiting their ability to communicate. They continue singing, but they can no longer be heard.
The different groups of cetaceans developed adaptations to the new environment: odontocetes (such as dolphins, killer whales and sperm whales) evolved to have a nasal vocal organ capable of producing high-frequency sounds and, in the case of dolphins, using them to echolocate; Meanwhile, mysticetes (such as the blue whale, the humpback and the fin whale) redesigned their larynx almost completely. This organ, one of the most complex in mammals, has two functions: protecting the airways and lungs and, on the other hand, phonation.
In most terrestrial species, this phonation involves the vibration of the vocal folds caused by the flow of air through the space between them, the glottis. But water forced radical adaptations. The result, particularly among some of the baleen whales, far surpassed the communication of their terrestrial ancestors: they are capable of emitting sounds that travel tens and even hundreds of kilometers. But most of what was known regarding the phonation system of these mysticetes was based on assumptions and inferences.
Between 2018 and 2019, a group of scientists specialized in cetacean phonation organized to obtain the larynx of some whales. They needed them as fresh as possible, it was the only way to be able to study them thoroughly. They contacted environmental organizations to notify them of any strandings. This is how they obtained this organ from three species of mysticetes, a minke whale, a northern whale and an imposing humpback whale. The latter is among the few species that have enchanted sailors for centuries with their calls.
Next, they dissected them to understand their anatomy in depth. In principle, they have all the elements present in the rest of the mammals, such as several basic cartilages for laryngeal articulation and sound production. But they do not have vocal cords like those of humans and other land animals and some of these cartilages have hardened and lost their original function. Instead, they have developed a U-shaped structure (seen from above) parallel to the trachea, which in these animals has a horizontal orientation and not vertical as in the human species. And above this shape, a pad of fat.
What the researchers did, which they have detailed in the magazine Nature, was to blow air into the larynxes mechanically to confirm his theory. They saw how the air made the arms of the U vibrate and, in its contact with the accumulation of blubber on top, low-frequency sounds similar to those emitted by these whales were produced. To do this, they used the air that entered through the nostrils to the lungs and, from there, they exhaled it once more to produce the sound. Up to here, as land animals do. But with whales they have the ability to reuse that flow that they seem to send back to the lungs and generate new sounds once more.
“They have developed new structures because the vocal cords would hinder rapid breathing at the surface”
Coen Elemans, expert in cetacean communication and acoustics at the University of Southern Denmark
“We believe that they developed new structures because the vocal folds would hinder rapid breathing at the surface,” explains Professor Coen Elemans, from the sound communication and behavior group at the University of Southern Denmark and first author of this innovative research. “Using these structures, baleen whales can make the very low-frequency sounds that they all make,” he adds. Although the physical mechanisms underlying sound production (vibrations induced by airflow) are the same as in human speech and singing, researchers have confirmed that “only a few species (humpback and bowhead whales) ) have redeveloped the ability to move the cartilage of the larynx and the thick tissues above these structures together. Like [hacemos los humanos con] our vocal cords”, he completes. This allows them to also emit high-frequency sounds, “the songs that most people know well,” she concludes.
In a second part of the work, following scanning the larynx of the humpback whale, they modeled it to study its behavior according to different physical and acoustic conditions. “Our model includes precise 3D shapes of the larynx and its muscles, which allowed us to simulate, for example, how the frequency is controlled by muscle modulation,” says Qian Xue, professor in the Department of Mechanical Engineering at the Rochester Institute of Technology, in a note. Rochester Technology (USA) and co-author of the study. His institutional colleague, Weili Jiang, added that her model accurately predicted the results of our experiments, “but we were also able to calculate acoustic characteristics that we mightn’t measure in the laboratory, such as frequency range.”
Among the results they obtained was a piece of information with great implications: the sounds they emit on the surface can reach the deepest part of the sea, but below 100 meters these whales cannot emit them. It is physically impossible for them. The problem is that this is the range that is becoming increasingly filled with sounds generated by human activities (ships, underwater mining, prospecting…). Combining these experiments and models, the researchers showed that baleen whales are physiologically unable to escape anthropogenic noise, because it masks their voices and therefore limits their communication range. As Elemans laments, “the limited frequency range (between 10 and 300 hertz) and depth (0 to 100 meters) where they can emit sounds overlap with the noise produced by humans; That’s why they can’t sing louder or deeper to avoid our noise.”
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