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"Ocean Noise"
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| By: LeRoy French Undersea Adventures 12 December 2008 |
;)
One of Jacques Cousteau's first films was entitled 'The Silent World".
This was filmed almost a half century ago and labeled our underwater
environment as a 'Silent World'. At the time this was true. Today not so
true.
Most marine mammals and fishes are very sensitive to sound. Noise travels long distances underwater and potentially prevents marine mammals and their young from finding their way. Some studies indicate that naval sonar affects large populations of whales. Seismic airguns used in gas and oil exploration are also a large contributor to ocean noise. It has been shown that these airguns have affected fish from over 500 meters to several kilometers. There are 40-80% fewer fish catches near seismic surveys. Reef fish can be impacted by these various sounds as they rely on normal reef noises to help them select a suitable habitat. However, whales seem to be the most vulnerable. They have been known to move away from feeding and breeding grounds along with altering their migration route and in some cases fallen completely silent. This means they are not communicating. Many have blundered into fishing nets and in some cases have collided with ships. This is most likely damage caused by ocean noise. Manmade ocean noise! The three main culprits in this noise pollution are; the increase in commercial shipping, seismic surveys and military sonar. All of these sounds make it increasingly difficult for whales and mammals to communicate with song. This also leads to mammal strandings. ;)
Today shipping lanes follow the coastal routes that whales have traced
for millions of years. The result has led to beach strandings, collision, and
basically disorienting the whales so that they lose their bearings.
Here is an interesting statistic. Climate change is not helping the problem
either. ''The acidification of oceans caused by rising temperatures
reduces sound absorption by 40%, therefore allowing sound to travel
even further.
WHY DO WHALES GET STRANDED? This has been a huge mystery for many years. There have been hundreds of studies made on this interesting phenomenon. It is believed that whales use a magnetic field and underwater topography to orient themselves. This means that any deviation to this field can cause confusion. It is not unusual for a beached whale after being returned to deeper water to later strand on the same beach from which it was freed. Whats happening is that the whales reference points lead them to believe that they are heading to deeper water when in fact they are going toward the beach. Aside from noise there are other factors involved. Whales may be hurt or sick. Also illness and parasites can affect their direction. What should be noted, is that when a whale is stranded and not able to get back into deeper water he will usually die. Keep in mind that the whales body is supported by the sea. On land the whale's body weighs it down and eventually may suffocate. Global warming, pollution, plastic bags, runoff, the list seerns endless. I realize there is very little the normal person can do about 'Ocean Noise', but I think it is irnportant that we are made aware of how our environment is affected by this type of pollution. Our underwater world is no longer a 'Silent World', just ask the whales. But shout loudly, because they're a little hard of hearing these days. |
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