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Whales are being drowned out by the sound of shipping
Whales are struggling to make themselves heard above the din in the oceans.
The same adaptations that allowed animals like the blue whale to communicate underwater now mean they can’t be heard above the propellers and generators of ocean-crossing boats.
The cacophony in the oceans is preventing whales from making themselves heard.
New research, published in Nature, reveals that the way baleen whale throats have evolved prevents them from singing outside the range of noise made by our ships. This means blue, grey and minke whales are finding it increasingly difficult to communicate in an increasingly noisy ocean.
Professor Coen Elemans, the lead author of the research, says, ‘Compared to the seventies, our oceans are now even more filled with human-made noise from shipping lanes, drilling activity and seismic guns.’
‘We need strict regulations on this noise, because these whales are dependent on sound for communication. We’ve show that despite their amazing physiology, they literally cannot escape the noise humans make in the oceans.’
Dr Agnese Lanzetti, who studies whale evolution at the Natural History Museum and was not involved in the research, adds, ‘Our disturbances take place on a scale of tens or hundreds of years, but evolution takes thousands or millions of years so it’s unlikely baleen whales will adapt to this noise any time soon.’
‘While specialised cartilage in some species, like the humpback whale, makes them better able to sing over anthropogenic noise, those without it are more likely to be lost if we don’t make efforts to quieten our ships.’
Baleen whales like the minke produce sound in a similar way to land mammals, but with adaptations that allow them to conserve air underwater. Image © Annie Leblanc/Shutterstock.
How the whale got his throat
Most mammals communicate by making sounds in their larynx, or voice box. This area of the neck contains the vocal chords that, along with the tongue, produce specific sounds by manipulating how air passes through them.
This system works just fine for most mammals living on land. But when the ancestor of modern whales and dolphins returned to the ocean between 40 to 50 million years ago, they had to overcome a variety of challenges that their land-living relatives didn’t face.
They needed to be able to hold their breath for an extended period of time, while also being able to open their mouth underwater. A terrestrial mammal doing this would risk wasting air or drowning.
One group of whales adapted to this issue by changing how they speak. The toothed whales use ‘phonic lips’ in their nose to make sounds which are focused by their skulls for echolocation and communication. This allows them to make sounds without using their larynx, which is sealed off while diving.
In contrast, the baleen whales don’t do this. While mysticetes are able to block their nose and mouth when breathing and feeding, how exactly they communicate has remained unclear.
‘Unlike toothed whales, baleen whales were seen as a bit boring because they don’t echolocate, instead communicating with low frequency sound,’ Agnese says. ‘Combined with the difficulties in studying these animals, this means that their sound producing mechanism had never been looked into before now.’
The new research finally offers the answer. Using larynxes taken from whales which had been stranded or accidentally caught in fishing gear, CT scans showed that the mammals have unique adaptations to use their larynx underwater.
‘We found that a u-shaped structure pushes against a big fatty cushion on the inside of the larynx,’ Coen explains. ‘When the whales push air from their lungs past this cushion, it starts to vibrate and this generates very low frequency underwater sounds which allow them to communicate over large distances.’
After the air passes through the larynx, it enters an air sac which then forces it back through the larynx and into the lungs. This means that the whale can continue to make sound while diving without wasting any air.
When it does finally come up to breathe, structures known as arytenoids help to keep the whale’s airway open so it can breathe deeply. These structures help to move the vocal cords in most mammals, but have become large cylinders which run the length of a baleen whale’s larynx to provide added support.
Together, these adaptations mean that even though they live underwater, the larynx of baleen whales works in essentially the same way as those of terrestrial mammals, including humans.
As propellers churn through the oceans, they make loud noises which can pose problems for a range of undersea wildlife. Image © Tawansak/Shutterstock.
Sounding off
While the changes have helped baleen whales adapt to a life underwater, the resulting trade-off means they can’t sing over a wide range of frequencies.
Simulations run by the researchers suggest that the structure of their larynx means that baleen whales can only communicate over long distances when they are less than 100 metres deep, and even then only at a maximum of 300 hertz.
While this hasn’t been an issue for millions of years, it now means they’re being drowned out by international shipping which operates in precisely this zone.
Large cargo vessels are at their loudest at these same low frequencies, reaching painful volumes equivalent to those of a jet taking off. This means that many baleen whales are stuck singing at levels within the background noise of these ships.
This is likely making it difficult for the whales to attract mates and communicate. But it’s also be important to know if the whales’ hearing can compensate.
‘We assume that baleen whales are good at listening to low frequencies, as these are the sounds they produce, but we don’t understand their hearing mechanism well,’ Agnese says. ‘It’ll be important to find out exactly how they hear to determine whether anthropogenic disturbances are preventing them from hearing the calls of other whales.’
The research also found that the outlook for some baleen whales is somewhat rosier. Bowhead, right and humpback whales have differently shaped arytenoids than other baleen whales which allows them to produce sounds that can reach frequencies as high as 6,000 hertz.
Though these higher-pitched calls travel shorter distances than lower-pitched songs, they are outside the range of shipping sounds which means they should still be able to communicate.
Ultimately, it’s up to us to quieten down the oceans. Even relatively simple changes like sailing slower can substantially cut the amount of sound shipping makes, and make the high seas a more pleasant place for whales to live.
