In his satirical Devil’s Dictionary, Ambrose Bierce defined the ocean as ‘a body of water occupying about two thirds of a world made for man – who has no gills’. Bierce may have been right to poke fun at human arrogance, but he underestimated the importance of the seas. Averaging almost 3,700 metres (12,000ft) deep, the ocean constitutes around nine tenths of the habitable space on our planet. It plays a commensurate role in the Earth system, not least as an engine – a ‘blue machine’ in the phrase that also titles an excellent book by the physicist and science presenter Helen Czerski – that moves heat around the planet.
The ocean has also been humanity’s get out of jail free card, absorbing more than 90 per cent of the additional heat trapped in the atmosphere by our greenhouse gas emissions. This grace period is, however, probably coming to an end. Worldwide, ocean surface temperatures have been rising faster than predicted, and have broken records almost continuously since March last year. In future, storms and heatwaves are likely to increase in intensity and frequency. Sea levels will rise further. Warmer waters will kill more coral reefs. Oxygen concentrations in the deep ocean will fall, and seawater continue to acidify.
Not everything is a story of catastrophe. When they are protected, ocean ecosystems can rebound remarkably quickly from overfishing, pollution and other human impacts. This is well attested in Helen Scales’s What the Wild Sea Can Be. No less vitally, the seas remain places of astonishing discoveries and wonders. Their past and future are full of potential as well as devastation, as James Bradley documents in Deep Water.
The impacts of noise pollution – above all from shipping, but also from other activities including seismic surveys beneath the seabed for oil and gas – may not be as serious and pervasive in the ocean as those of climate change, but they can be devastating to marine life. The challenges are well described in Sounds Wild and Broken by David Haskell and The Sounds of Life by the late Karen Bakker – two books which, in different ways, explore the vital role of sound in the lives of both marine and terrestrial creatures. And now Amorina Kingdon’s Sing Like Fish, with its focus solely on the natural and human history of sound in the ocean, brings fresh energy, intelligence and insight to a fascinating and rapidly developing field.
Kingdon ranges from the evolution of hearing in fish and other marine organisms to the human discovery of sound beneath the sea, the development of sonar for submarine warfare, and far beyond. She takes her title from an observation by Kieran Cox of Simon Fraser University, Vancouver, who researches how coastal kelp forests attenuate sound waves and in doing so may provide a haven for sealife from shipping noise. Cox tells Kingdon: ‘People tell me that fish sing like birds, but, strictly speaking, fish evolved millions of years before terrestrial animals including birds. Birds sing like fish.’ The point is that our prejudices have things precisely backwards. Far from being silent, as Jacques Cousteau’s stubbornly enduring but utterly mistaken phrase had it, the seas are full of noises at every scale, and always have been. Sound travels over four times faster in water than it does in air, while light attenuates rapidly, and many creatures have evolved to take advantage of this.
To Kingdon’s ear, the most
beautiful underwater sound
is the trill of the bearded seal
Popular science writing about sound in the oceans often highlights cetaceans – that is, our fellow mammals the dolphins and whales, who use sound for echolocation or to create beautiful and elaborate songs. Almost every month, it seems, there are astonishing discoveries in this field. The most recent include AI-aided advances that offer tantalising glimpses into what some of them may be saying to each other. But one of the joys of Kingdon’s book is that she looks elsewhere to areas that get much less attention but are no less extraordinary.
There is, for example, a largely neglected or forgotten history of how natural philosophers and scientists found out (and almost forgot) that fish can hear at all, how fish make sound, and how they locate its direction. Some observations date back to antiquity. Pliny the Elder described how pet fish in the emperor’s aquarium would come in answer to their names. But many of the most remarkable discoveries were made in the 20th century by scientists such as the splendidly named Marie Poland Fish, who showed that fish have the widest variety of sound making structures of any vertebrate group.
Some fish scrape and stridulate. Others drum on their swim bladder with special muscles and tendons, making resonant hums, moans and bloops. Yet others scrape or grind special teeth in their throats. And others again deliberately burp or expel gas from their anus.
‘Underwater sounds,’ writes Kingdon, ‘range from funny to gorgeous to, honestly, kind of boring.’ To her ear, the most beautiful sound is the trill of the bearded seal. I tend to agree. Hearing their fluting calls, a mixture of Clanger and penny-whistle, echoing deep through the quiet water in the Arctic seas around Svalbard is one of the most memorable sonic experiences of my life.
Her conclusions, too, are – forgive the pun – extremely sound. Noise pollution, she writes, does not match the deep threat posed to the oceans by climate change, but acoustics are a fundamental part of marine ecosystems, and humans would be wise to be a lot more careful. ‘Opinions on how to regulate may vary, but the science is getting clearer on what to regulate.’ The chief culprit is shipping, and part of the good news is that improved ship design and smarter navigation can cut costs and reduce impacts on the living world.
Kingdon observes that there are economic reasons to reduce shipping noise – more efficient ships are cheaper to run. But for her, the intrinsic value of nature is even more important. The sonic wonders of the ocean reveal a world ‘so much bigger than we know. So much stranger and richer.’ Exploring it, she says, makes us fully human. ‘It’s a priceless thing.’
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