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!
Proceedings of Meetings on Acoustics (4th International Conference on the Effect of Noise on Aquatic Life, 2016. All manuscripts are open-access): http://asa.scitation.org/toc/pma/27/1?expanded=27
Buscaino, G., Filiciotto, F., Buffa, G., Bellante, A., Di Stefano, V., Assenza, A., Fazio, F.,
Caola, G. & S. Mazzola. 2010. Impact of an acoustic stimulus on the motility and blood
parameters of European sea bass (Dicentrarchus labrax L.) and gilthead sea bream (Sparus
aurata L.). Marine Environmental Research 69: 136–142.
Codarin, A., Wysocki, L.E., Ladich, F. & M. Picciulin. 2009. Effects of ambient and boat
noise on hearing and communication in three fish species in a marine protected area
(Miramare, Italy). Marine Pollution Bulletin, doi:10.1016/j.marpolbul.2009.07.011.
Jasny, M., Reynolds, J., Horowitz, C. & A. Wetzler. 2005. Sounding the depths II: the rising
tools of sonar, shipping and industrial ocean noise on marine life. Natural Resources
Defence Council Report 2005, New York, USA. 84 pp.
McCauley, R.D., Fewtrell, J. & A.N. Popper. 2003. High-intensity anthropogenic sound
damages fish ears. Journal of Acoustic Society of America 113:638–642.
Slabbekoorn, H., Bouton, N., van Opzeeland, I., Coers, A., ten Cate, C., & A.N. Popper.
2010. A noisy spring: the impact of globally rising underwater sound levels on fish. Trends
in Ecology & Evolution 25(7): 419-427.
Tasker, M.L., Amundin, M., Andre, M., Hawkins, A., Lang, W., Merck, T., Scholik-
Schlomer,A.,Teilmann, J., Thomsen, F., Werner, S. & M. Zakharia. 2010. Marine strategy
framework directive. Task Group 11 Report. Underwater noise and other forms of Energy.
JRC Scientific and Technical report. http://www.ices.dk/projects/MSFD/TG11final.pdf
Vasconcelos, R.O., Amorim, M.C.P. & F. Ladich. 2007. Effects of ship noise on the
detectability of communication signals in the Lusitanian toadfish. Journal of Experimental
Biology, 210: 2104–2112.
Wysocki, L.E., Dittami, J.P. & F. Ladich. 2006. Ship noise and cortisol secretion in
European freshwater fishes. Biological Conservation 128: 501–508.