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Dolphins under the sea

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How frustrating is it to have a conversation while someone is jackhammering nearby? Or drilling perhaps? You have to raise your voice, repeat your words, and even then the person you are talking to might misunderstand what you are trying to convey. Or perhaps your response is that of my Mom’s regarding my music habits – “Turn that down I can’t hear myself think!”. With the advent of the industrial revolution the amount of machinery producing noise increased dramatically, not only on land, but in the water as well. Oceans have never been a silent place, though perhaps not as raucous as The Little Mermaid or Finding Nemo may suggest! Ocean dwelling creatures had the time to adapt to the natural noise of their environment (caused by weather, seismic activity, and biological sources), but due to the relatively rapid and recent advancement of civilization they have not had time to adapt to anthropogenic sources of noise in the ocean.

Sounds travels much better and further than light in the ocean, and as a result marine mammals use sound instead of light to find food, communicate, detect predators, and navigate. As a result of anthropogenic noise in the ocean marine mammals may experience behavioural alterations, auditory masking, physiological damage and potentially death. Research has shown that dolphins have a number of reactions to the sound (and presence) of boats which fall into three categories: behavioural reactions, acoustic reactions, and directional heading patterns; acoustic reactions include changes in the type and timing of vocalisations; and physiological reactions include changes in heart rate and respiration.

With this in mind the restrictions placed on boats regarding how close and how long they are legally allowed to spend with dolphin pods are entirely understandable!

Written by: Minke Witteveen

For further reading:

  • Branstetter, B.K., Trickey, J.S., Bakhtiari, K., Black, A., Aihara, H. and Finneran, J.J. 2013. Auditory masking patterns in bottlenose dolphins (Tursiops truncates) with natural, anthropogenic, and synthesized noise. Acoustical Society of America 133: 1811-1818.
  • Nowacek, D.P., Thorne, L.H., Johnston, D.W. and Tyack, P.L. 2007. Responses of cetaceans to anthropogenic noise. Mammal Review 37: 81-115.
  • Van Parijs, S.M. and Corkeron, P.J. 2001. Boat traffic affects the acoustic behavior of Pacific humpback dolphins, Sousa chinensis. Journal of the Marine Biological Association of the United Kingdom 81: 533-538.

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