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Aquatic habitats are no “silent world” as Jacques Cousteau has written. They are filled by several, different sound sources. Waves and water turbulences are just some example of physical sources of sounds, but physical sources are not the only ones. An immense variety of aquatic animals depends on sounds for activities that are crucial for their survival, and their vocalisations are called by scientists “biophony” (the symphony of life). Marine mammals are the ocean’s most famous singers, but fish vocalise too. More than 800 species of fish depend on sounds to survive and reproduce. Fish sound production is especially conspicuous during the reproductive season and is typically related to agonistic interactions and mating activities.
In the last fifty years, human activities have radically changed aquatic environments by adding incredibly numerous sources of noise. Small boats, commercial boats, seismic exploration, military activities, windfarms, pile driving…anything but a “silent world”, we are actually creating an ocean of noise. The most common man-made source of noise is shipping. The rumble of engines, propellers, and other commercial shipping noise can be heard in virtually every corner of the ocean. In a world in which 80% of global trading takes place at the sea, the number of merchant ships has tripled in the last 75 years and the number of recreational boats keeps increasing as well. Vessels noise in coastal area has become a form of chronic, constant pollution.
Anthropogenic noise is now recognised as a significant pollutant in the marine environment, and the potential consequences for animal survival are of international concern. Some species may acclimatise to noise after chronic exposure, others may struggle to develop and survive. Considering the global extent and the wide range of effects of noise pollution on aquatic life, man-made noise has been identified as a target for the monitoring of a good quality coastal environment in both Europe and USA (e.g. inclusion in the US National Environment Policy Act and in the European Commission Marine Strategy Framework Directive).
But which type of effects can noise have on aquatic life? If they can, animals try to escape from noise, possibly giving up to other important activities, such as feeding and reproduction. For example, avoidance reactions to vessel noise have been noticed in several fish species such as herring, cod, rudd and roach. And if they can’t escape, physiological effects can be expected. Exposure to noise causes stress to several fish species: their heart bits quicker, they move more and their stress hormones increases. Anthropogenic noise can also have other physiological effects. The brown shrimp, for example, grows less, reproduce less and its mortality rate increases; other fish species grow less and produce less viable eggs.
When the situation gets louder, an immediate physiological response has been noticed in several species: a temporary threshold shift. Is basically what happens to us after spending a night out in a really loud place, like a nightclub. For a short period of time, we do not hear very well: this happens because our hearing threshold has shifted a little bit up, meaning that the exposure to noise has temporarily compromised our hearing capabilities. Of course, if the noise is too loud or the time of exposure is prolonged, aquatic animals suffer of a permanent hearing damage: in other words, their hearing ability is permanently impaired. Sometimes, with very loud sounds like the one used in military activities and in seismic surveys, this damage can be so severe to make animals literally deaf or, worst, death. The continuous and increasing level of anthropogenic noise can also make impossible for animals to hear important signals, like predator noises or mate calls. As it happens to us when we try to speak in a noisy place, animals in a noisy environment simply do not hear each other and the communication is difficult, if not impossible. And if the communication was oriented to finding a mate…this could not lead to an unhappy ending…
Raising our awareness to the problem of underwater noise pollution can help us lower man-made volume, in the oceans and in freshwaters. Aquatic animals would surely thank us for it!
Want to learn more?
Check the video we produced, give a look to the reference lists below and…help us spreading the voice!
Which is the level of public awareness on marine pollution?
New video on Artemis Eyes Channel!
(Youtube link: Marine Pollution Awareness- video)
In December 2015, an online survey was made public on the ec.europa.eu website; the survey was about public perception of marine pollution. The questions were few and simple: do you think that chemical pollution is an issue for aquatic environments? What about plastic pollution? And climate change? Do you consider noise pollution a threat for aquatic ecosystems? The same questions were asked in the streets of Galway, in May 2016.
The results of this survey show that the level of public awareness is quite satisfying when it comes to chemical and plastic pollution, and also climate change seems to be now recognized by most people as an issue for aquatic ecosystems.
But what about noise pollution?
Anthropogenic noise acts on a global scale, results from a variety of sources and produce several different effects on the aquatic fauna (and ultimately, on the human kind as well). However, public awareness around this particular and urgent environmental matter is very low, and surely it’s not in line with the level of knowledge achieved to date by scientists researching anthropogenic noise.
Do you want to learn more about anthropogenic noise?
Check the Playlist “Noise Pollution” on the Artemis Eyes Project channel: Noise Pollution playlist
Please, like and share this playlist in order to help us raise awareness around this urgent environmental matter!