The buzzing sounds from the engines of commercial ships along the sea routes not only alter whale behavior but also affect other giant mammals underwater. Noise affecting their brains causes stress and discomfort, a new study suggests.
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The researchers said the first findings stem from the attack on the twin towers of New York, USA on September 11, 2001, an event that seemed to have no impact on the lives of aquatic animals. They explained the catastrophe that caused maritime transport to drop abruptly and affect the level of sound pollution under the sea.
For the past 50 years, noise caused by military ships, cargo ships or oil exploration equipment with high decibel levels (units of pressure and sound intensity) is gradually increasing in intensity and range.
The type of horned whale is connected at low frequency from 20Hz to 200Hz. Some other species adapt by producing a louder and more frequent sound signal.
Summer before the 9/11 event, Rolland Rosalind expert at New England Aquarium, Boston conducted research on bullhead whales in the North Atlantic. He raised and watched a number of baby fish in Fundy, Canada.
From 2001 to 2005, scientists used professional dogs to find whale feces, floating on water. They collect samples over a period of 6 weeks in a year.
Scientists discovered hormones related to glucocorticoids, reflecting the level of stress that can change in a day, days or even hours.
When the level of underwater noise decreased, the researchers realized this was an opportunity to investigate: "Is sound pollution the cause of stress for the bullhead?"
They found that changes in hormone levels were consistent with the sudden drop in maritime traffic in the region.
"We believe that the decrease in vessel traffic is the main cause affecting whale numbers , " according to the study published in Proceeding of the Royal Society B.
Glucocorticoid is secreted when animals encounter crisis due to invasion of foes or famine, dryness of water. Initially this hormone quickly helps animals cope by using stored energy. But if this hormone is constantly high due to long-term stress, it will cause harm, leading to growth retardation, weakening the immune system and affecting reproductive capacity in this system.
Terrestrial animal studies have shown that chronic stress may be caused by snowmobiles or by road vehicles.
North Atlantic bull whales live and grow near the shore so they are extremely dangerous. They are threatened by ship collisions or entangled with fishing tools, two leading causes of death for large marine mammals.
"The human sound pollution is unclear. But we can easily see its negative consequences for the development of whale populations in the coastal area," the experts concluded.