Underwater, where animals have little reliance on sight, the acoustic panorama is particularly important for perceiving the environment. A review recently published in Science traces the impact that noises generated by human activities have on marine fauna: direct damage, for example, to hear, but also indirect damage that affects communication, reproduction, and foraging. We talk about it with Gianni Pavan, director of the Interdisciplinary Center of Bioacoustics and Environmental Research of the University of Pavia, Department of Earth and Environmental Sciences.
Unless you are a regular in diving, we might think that underwater life is much quieter than that on land: a muffled world in which sounds are barely perceived. But the acoustic panorama of the sea is by no means poor above all, it is not without an ecological role, because each of the sounds that propagate under the waves is used by animals, either for courtship, or to identify an oncoming predator vice versa, to identify prey. The problem, as a review recently in Science explains is that now there is too much noise and we speak of noise in the biological sense that is unwanted and unnatural acoustic signals that disturb or even harm animals. In the Anthropocene era, the acoustic landscape of the sea is dominated by anthropophagy, which has profoundly negative effects on a multitude of species.
Many marine animals produce sounds of various kinds and for various reasons. The vocalizations of the cetaceans, a privileged method of communication for this group, are perhaps among the most famous: they range from the whistling of dolphins to the “click” of sperm whales, to the complex songs of humpback whales, capable of spreading for over 100 kilometers. Although they are the best known, the sounds produced by cetaceans are not the only ones to enrich the biophony (i.e. the set of sounds of biological origin) in the sea for example, some fish such as cod and grouper use the sounds to aggregate and coordinate spawning.
And even those who do not vocalize produce different sounds, for example, related to foraging as an article explains on Il Bo Live, for example, the crackle that can sometimes be heard when swimming underwater near a reef is produced by the gun shrimp of the Alpheidae and Palaemonidae families which quickly open and close the claws to feed and defend the territory.To this complex acoustic panorama is added the set of sounds produced by natural phenomena, defined geophony the wind and rain on the surface of the water, or also, in the polar regions, the ice that forms and breaks.
These are all important sounds for animals that live below the surface of the sea where it is difficult to rely on the sense of sight and hearing plays an important role in understanding the surrounding environment. Sounds allow communication between individuals and in the group, for reproduction and foraging they provide information on what is happening in the surrounding environment, allowing for example to warn the approach of a possible predator and perhaps even to guess its size. They can even help some coral reef species, in the larval or juvenile stage, to identify the right habitat in which to settle.
A Sea That Is Too Noisy
But all these sounds are changing. Human activities have altered biophony and geophony and, directly or as a byproduct of other activities, have added a third and prevalent component anthropology, write the authors of the review in Science. In short, the noises derived from our activities are added to the acoustic landscape of the sea. Some, as reported in the white paper Control and reduction of anthropogenic noise in the Italian seas and reduction of its effects of 2017, are the direct product of certain activities, especially industrial ones (for example mining exploration, or the construction of wind farms, or work on the coast) and military ones (for example the use of sonar and explosions). But another part of the anthropology, defined as diffuse noise, is instead the indirect product of ship traffic, from hundreds of thousands of boats always sailing in every part of the globe.
Do acoustic tests cause whale stranding? was the question he called a short letter published in Nature in 1998. In a few lines of text, Alexandros Frantzis, of the University of Athens, reported the case of stranding of 12 wifi, in the space of two days, along the coasts of the Gulf of Kyparissiakos. The necropsies performed had not revealed particular abnormalities and, in search of a possible cause of such a significant stranding, Frantzis had indicated the possible connection with the research ship of the NATO Alliance which, in those days, was testing a sonar system for the detection of submarines. It seemed unlikely, was the letter’s conclusion, that the two events were unrelated.
That communication led to a commission of inquiry that established the probable cause and-effect link between the use of sonar and damage to animals, marking the beginning of much of the research aimed at investigating the impact of noise pollution on marine fauna explains Gianni Pavan, director of the Interdisciplinary Center of Bioacoustics and Environmental Research at the University of Pavia. The first concerns were for cetaceans, both because they are charismatic animals and because they are very sophisticated in their sound communication here their voices. But over the years the interest in the effects on other marine animals has also increased because we know that each species has its own role in the complex acoustic ecosystem of the sea. What, then, are the effects of anthropology on marine fauna?
The Impacts Of Anthropology
Anthropology can have different impacts depending on the type of noise produced, its location, and its duration. And none of these impacts are to be underestimated. High-powered noises, such as those from airguns used in geophysical prospecting or naval sonar, can cause direct damage, such as temporary or permanent deafness, but also other types of mechanical trauma, embolism, and hemorrhage. Although less immediately and dramatically, even the faintest noises can have negative effects. ‘Even when the noise is at a level that would not appear physiologically harmful, whether it is long-lasting or continuous it can have a major effect on animal behavior. And this is particularly harmful in the sea, where sound is the essential key to perceiving and understanding the environment, explains Pavan. Noise generates stress and prevents us from clearly perceiving other sounds, interfering with both communication and the perception of the environment. In turn, this can have negative effects on courtship, and therefore on reproduction, on the ability to signal dangers, or, in the case of cetaceans, to identify prey with the biosonar. It can also cause animals to leave certain areas or migration routes.
At sea, even more than on land, noise pollution can have important effects not only on the individual but on the entire population. The marine acoustic environment is normally more extensive than the terrestrial one. In the case of cetaceans, for example, we know that communication can take place hundreds of kilometers away, continues the professor. “And every 6 decibels of noise increase halves the distance at which you can communicate. Fin whales court each other, to reproduce, at 100 km; it is, therefore, sufficient to increase the background noise by 6 decibels, and communication will be reduced to 50 kilometers. Another six decibels, and to hear they will have to get closer to 25 kilometers. For this reason, it is estimated that for many whales the possible communication distance is reduced from 100 to 1 due to general noise.
On which, however, all the other noises are added. This is also because one of the main differences between marine and terrestrial noise pollution is in the propagation capacity of sound which, especially at low frequencies, can propagate much faster and affect a much larger area. So, for example, a seismic campaign will not only produce a very strong noise in the area where it takes place but it will also be perceived hundreds of kilometers away, for example by completely masking the sounds of whales.
Furthermore, as the Science review specifies, although it is predominant, anthropology is not the only element to alter the acoustic panorama of the sea. The sounds produced by our activities are in fact accompanied by an alteration of biophony and geophony, which is also anthropogenic: for example, the hunting of large marine animals (especially whales and pinnipeds) and the degradation of ecosystems such as coral reefs and kelp forests and marine plants have reduced the population of various animals, and consequently the related biophony. While the climate crisis has the dual effect of altering the biophony by changing the composition of species in certain ecosystems (such as, again, coral reefs) or by changing the distribution of species, and of influencing the geophony, altering rainfall, winds, the formation of ice. These elements contribute to each other in producing effects on animals and marine ecosystems.
Towards Quieter Waters
If on land we can and do try to contain noise with different strategies, also because of the widely recognized negative effects for our species (the European Environment Agency estimates that noise pollution contributes to 48,000 new cases of cardiac ischemia every year and 12,000 premature deaths in Europe), things are a bit more complicated at sea, because it is difficult to imagine, for example, noise barriers like you can do with a motorway. Finding solutions to limit marine noise pollution is however essential, also because human activities at sea are increasing. For example, according to a study published in Nature Sustainability, maritime traffic can increase from 240% to over 1,000% by 2050. And, as an article on Il Friday di Repubblica, the interest in the extraction of minerals from the seabed is increasing, because many materials will be increasingly sought for alternative energies.
In general, we are now fully aware of the problem also for marine ecosystems, explains Pavan. Noise is recognized as a marine pollutant in the 2008 European Marine Framework Strategy, and the International Maritime Organization approved 2014 specific guidelines for the reduction of noise pollution from boats. In general, the front on which the most work is done to stem the problem is the reduction of noise produced by ships or other structures based on new technologies. In some states, for example in some ports in Canada, quieter ships are also incentivized with discounts on port taxes, ”continues the researcher. “The reduction of noise can also be implemented, in some critical habitats, with the reduction of speed, for which regulations are also being studied for the reduction of speed in some areas, which would also contribute to reducing the problem of collisions, which is especially important for species close to extinction.
As for other sources of noise, like an airgun, sonar and drilling, there are regulations now accepted in almost all countries to control emission levels and prevent danger thresholds from being exceeded. Very variable regulations and recommendations from one country to another then envisage evaluating how much noise will be produced by a given activity and its environmental impact, and then preparing mitigation systems, which can be technological or approach changes (for example screwing instead of the plant a pole) or based on inspection to check that there are no cetaceans in the area affected by excessive noise, ”explains Pavan. In short, there are several strategies available. Now, the authors of the review on Science conclude, it is a matter of incorporating them into binding international conventions to support, with a sustainable economy.