Sounds of the Sea
The noisy oceanSound travels well in water and the sea is a very noisy place. If you listen with a hydrophone (underwater microphone) you will hear boat engines, construction noise, and if you're lucky, the sounds of the animals who live there, including whales and dolphins. Dolphins & Porpoises Dolphins and porpoises use echo-location (sending out a pulse of sound and listening to the returning echo... through their jawbone!) to find their food, to communicate with each other and to find their way around the ocean. The Song of the Whale team studies whales, dolphins and porpoises by listening to the sounds that they make. Their clicking, whistling and moaning sounds can tell us a lot about them, including which types of whale are present, and where they are. Scientists have discovered that each dolphin makes its own unique whistle. Individual dolphins can be identified from these whistles. Mothers and calves have similar sounding whistles. Shhh… listen to the sounds of porpoises! Sperm whales Sperm whales make loud, regular clicks, called echolocation, when diving. These clicks bounce back off surrounding objects and allow the whale to 'see' underwater using sound. They may also click to each other to stay in contact, and sometimes use short sequences of clicks called 'codas' to communicate in social situations. Shhh… listen to the sounds of sperm whales! Human-made ocean noiseIn busy waterways, human-made ocean noises can occur ‘on top’ of one another creating a sonic soup! SONAR (SOund NAvigation and Ranging) Active sonars are devices used for detecting objects underwater. They emit ‘pings’ that travel through the water, bounce off a target and then return to the sonar. The time delay of this echo can be used to measure the range (distance?) to the target. More sophisticated sonars are used by the military to search for submarines underwater. Unfortunately, the power levels of these sonars need to be high to ‘see’ large objects underwater and it seems that these loud sounds can harm, and even kill, some whales. A group of whales called the beaked whales seem particularly vulnerable to these sounds and a number of mass strandings have been linked to military sonar. Shhh… listen to the sound of a sonar ping! Seismic Surveys Seismic surveys are carried out by boats looking for oil and gas reserves in the sea bed. The boats trail long lines or airguns behind them and these airguns create huge bangs every 10 seconds or so. These loud sounds head down to the seabed, and bounce back up to the surface where the echoes can be processed to identify any likely pockets of oil. Although the example here sounds quite quiet, it is actually one of the loudest man made sounds in the sea; the loud underwater bangs are often heard hundreds of kilometres away. Whales have been known to move away from these intense sounds. Shhh… listen to the sound of a seismic airgun bang! Shipping Any boat with an engine produces noise at sea. Engine noise sounds like a low rumble, much like a car engine. Although shipping noise is not as loud as sonar or seismic sounds, the high number of vessels around the world means boats are major contributors to global noise levels. Surprisingly, quite simple things like having a rusty propeller can make a boat much noisier. Often, the behaviour of whales and dolphins will be affected a long time before we can even see them at sea. |
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Beaked whales, like the Cuvier’s beaked whale in this photo, seem particularly vulnerable to active sonar and a number of mass strandings have been linked to military sonar. |
