The World of Silence (Le Monde du Silence in its original name in French) was a documentary film made in 1955 by explorer and marine biologist Jacques Cousteau along with filmmaker Louis Malle. It won the Palme d’Or at the 1956 Cannes Film Festival and was hugely successful. Its title was the same as the first book published by Cousteau. But above all, this title propagates a myth that the seabed is a silent place. This idea is wrong; there is noise in the oceans, there has always been noise and it is increasing all the time. And that is not good.
“There’s a lot of noise down there,” says Soledad Torres-Guijarro, a professor at the University of Vigo. She knows this well, because her research focuses on collecting, “fishing,” according to the scientist, ocean sounds of anthropocentric origin, i.e. those produced by human activities. In 2016, the telecommunications engineer created a database for underwater noise: “When we started looking at underwater acoustics, we realized that there were no public databases for noise from shipping. Taking advantage of the fact that we live in Vigo and sail many boats through the estuary, we recorded and created the database that we share with more than 300 research groups from around the world. And we have developed an application to visualize the noise of the estuary at a specific point in time on a map.”
These anthropocentric sounds in the sea have become a serious global problem because they affect the physiology and behavior of the creatures that live in it. International organizations recognize anthropocentric marine noise as a major environmental stressor that can have catastrophic consequences for the survival of populations and even entire species. “For a long time, the focus has been on whales. But for a decade, research has also been done on how underwater noise affects the rest of the creatures living there, and it is estimated that around two-thirds of them suffer from the effects of this pollution,” says Torres-Guijarro.
There’s a lot of noise down there; the focus was on whales, but now we know that two-thirds of all marine animals suffer from this contamination
Soledad Torres-Guijarro, Professor at the University of Vigo
Sea creatures also make sounds like they live on land. Marine mammals have evolved to use sound as a source of information. “We record dolphin whistles in Cortegada, one of the Atlantic islands of Galicia. There we have a permanent hydrophone that also has a detector for those whistles. The theme of dolphin communication is very cool. Recent research has found that each person has a specific recognition call, i.e. a proper noun, and that their mode of communication also has grammar, which means it is a language,” explains Torres-Guijarro.
Dolphins and other marine mammals and birds perceive sounds through pressure, just like humans. This is not the case for most fish and marine invertebrates, which do not have hearing. However, this does not mean that they cannot perceive the effect of the sound, what they perceive in their case is the movement of the particles that create the sound in the water. And this movement of particles can do the same damage that noise does to mammals and birds.
All these noises are caused by different activities: “The biggest noise pollution is caused by shipping, it is an almost continuous activity and it takes place in practically all seas. And then there are activities that create noise, which can be very harmful because they are very energetic but much more concentrated in space and time. One of them is seismic exploration campaigns on the seabed to determine if there is gas or oil there. The problem is that compressed air cannons are used, which emit very high-energy sound pulses, in order to analyze their echo and gain information about the subsoil,” says Torres-Guijarro.
But besides these activities, according to Torres-Guijarro, there are many others: “There are construction works on or near the coast, which can be very noisy. And sonar from ships can also be very harmful because some are very powerful, especially those from warships.”
The problem with underwater noise is not only that there are many of them, but also that sound travels particularly well in water: “The difference between the way sound travels in air and in water is that it travels much faster in water, until to four times faster. And it goes further, sometimes to enormous distances of hundreds of kilometers,” Torres-Guijarro illustrates.
The average noise level in the 63 Hz frequency band between July 2018 and June 2019. The red lines represent the ships’ most frequent routes. The author of the tool is David Santos, to whom Soledad Torres-Guijarro addressed the thesis.
This ability of water to emit sound has been used by many sea creatures to develop many abilities such as The fact that there is constant or frequent noise in the underwater world disturbs the sounds of the animals and makes life difficult for them.
The scientist develops it: “In two experiments, we are investigating how noise affects two types of mussels: mussels and mussels. In the lab, we excited mussels and clams with speakers that reproduce underwater noise conditions. We already have the results of the experiment on mussels that we conducted with biologist José Gabarro from the CSIC Institute of Marine Research, and they are quite conclusive. If you expose the clam to a certain level of noise, it will shut down, and a clam that shuts down won’t eat, which in the long run is detrimental to its health and likely growth. We’re not done with the shells that we’re making with biologist Elsa Vázquez from the University of Vigo, but we’re beginning to see them burying themselves in the ground. For the same reason as the mussel they feel threatened and with the same consequences, if they burrow they don’t eat and if they don’t eat they don’t grow”.
Professor Torres-Guijarro “fishes” underwater sounds of anthropocentric origin and visualizes them in an application Reyes Novoa Carballal
For the Galician researcher, underwater noise not only means stress for the species that live in the oceans, but “creates an intolerance to life in many places,” she concludes.
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