Sound At Sea
Boats, helicopters, boreholes, sonars, windmills … Noises of human origin have a worrying impact on marine animals. Researchers are trying to find out more about this noise pollution and its effects on wildlife.
Living in a house with single glazed windows overlooking a highway, does not tempt you? If shorebirds are to be protected from road traffic, it seems necessary and even obvious, the question also arises at sea. Where shorebirds are none other than marine animals and where the issue of anthropogenic noise, that is to say of human origin, is more and more prevalent. Especially because specialist bioacoustics and researcher at the Information Sciences Laboratory and systems, the Mediterranean, the fleet of cargo, freight and cruise double every three-four years. And who has not already experienced the deafening buzz of these big boats? This sound is heard not only in the air, but even more under water, because of the acoustic laws (the sound propagates faster in the water than in the air and affects the bottom and the area).
Acoustic Pollution Is Up Sharply
The crescendo of acoustic pollution depends not only on the rising frequencies of the seas, but also on the increase in the speed of boats. “A big boat going slowly is quieter than a jet ski fast,” says Hervé Glotin, who analyzes the sounds produced by whales and their behavior from anthropogenic noise.
The ships are not therefore solely responsible for these nuisances. The engines of small recreational vehicles also add to the problem. Like military exercises using sonars, boreholes, seismic explorations using acoustic guns for oil exploitation, offshore extraction sites or renewable marine energies, such as the noise of the blades in The large wind farms or the shelling necessary for their installation in the marine subsoil.
The problem is that these noises can be a source of confusing stress to marine fauna. For example, in Mediterranean waters between Marseille and Le Lavandou, live twenty Tursiops truncatus , these dolphins live in shallow waters near the coast. Their population is threatened by the coastal tourist activity: they are observed less and less near the big cities. A study by a student Isabelle Charrier, a specialist researcher at the Institute of Neurosciences Paris-Saclay, went out to observe fur seal behavior changes in Australia according to the playback of boat noise; it showed that at a great amplitude their vigilance increased to such an extent that it prevented any other parallel action, such as that of suckling the young.
Many Noise-Related Cetacean Accidents
This stress induced by acoustic nuisance can lead to the death of some animals, sometimes even more directly. In particular, by causing diving accidents, for example in beaked whales: very sensitive to the sound of military sonars or mining prospectors, these cetaceans will leak to the surface without any stage of decompression, which will cause a lethal embolism. Now these mammals are “diving professionals” says Isabelle Charrier. And such accidents are not customary outside of any human sound intervention. “The passage of boats and even a helicopter or a plane at low altitude can also lead, within the rallies walruses on land or ice blocks, a crowd movement, as in humans. All the individuals will flee to the water and, in panic, young will be completely crushed. This type of scramble has already occurred in Alaska, with hundreds of deaths, “says the researcher.
If fish larvae grow slower in noisy environments, says Hervé Glotin, the impact of this noise pollution is felt to excess in animals using acoustic signals to move and locate their prey, as is the case of odontocetes, cetaceans with teeth. Few internal lesions are lethal, as this implies close contact of the animals with the source of the noise and a high acoustic power. But some audible aggressions can damage their hearing systems, even temporarily. As a result of these injuries stranding or percussions with boats, due to poor analysis of the environment in which the animals move, or malnutrition due to a lower prey detection.
In the mysticetes, baleen whales, communication between individuals of the same species can also be affected. Noise reduces the detection distance of blue whales, Hervé Glotin notes, and fragment their communication networks. The result is less genetic mixing and embrittlement of the species, which may jeopardize its survival. In the same vein, the songs of humpback whales turn very quickly: “If you change the spread of songs by anthropogenic effects, it could isolate individuals whose acoustic productions are no longer appropriate.
Inadequate Protective Devices
The other problem is that the solution to all these noise nuisances is not obvious. If France recognizes since 2010 noise pollution as one of the forms of marine pollution, there is no clear regulation. Not all species are affected by a single noise. Measures, performed by the sonobuoy Bombyx and must be further developed, allowed to note that the behavior of sperm whales are changed less than those of striped dolphins in the presence of noisy boats, said Hervé Glotin. It is therefore not enough to impose a threshold of decibels not to be exceeded, in particular by regulating the speeds of the boats. Especially since a boat that is too quiet can also surprise the animals on the surface. Many fin whales have been hit by vessels they had not heard: “The engine is located at the rear, and the bow is the mute point of the boat,” the specialist bioacoustics. The noise can sometimes be used, at low power, to gently warn the animals of an area before the engagement of very noisy works.
In the case of shelling to install wind turbines or construction of the coastal road on Reunion Island, the installation of “bubble curtains” made it possible to mitigate nuisances by reducing the propagation of acoustic waves , But the operation of these air balloons attached to each other is optimal only in case of calm sea. Another protocol is fairly simple to implement and is described by the doctoral student Berkowitz, the Marine Mammal Observers, which monitors the presence of animals in the vicinity during operations. But the effectiveness of this device remains unsatisfactory and diminishes even more when the work continues at night or the animals are in submersion.