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Scientists have long known that some beaked whales beach themselves and die in agony after exposure to naval sonar, and now they know why: the giant sea mammals suffer decompression sickness, just like scuba divers.
At first blush, the explanation laid out Wednesday by 21 experts in the Proceedings of the Royal Society B seems implausible.
Millions - Years - Evolution - Whales - Machines
Millions of years of evolution have turned whales into perfectly calibrated diving machines that plunge kilometres (miles) below the surface for hours at a stretch, foraging for food in the inky depths.
The heart rate slows, blood flow is restricted, oxygen is conserved.
Ocean - Deep-sea - Diver - Nitrogen - Bubbles
So how could the ocean's most accomplished deep-sea diver wind up with nitrogen bubbles poisoning its veins, like a scuba novice rising too quickly to the surface?
Short answer: beaked whales—especially one species known as Cuvier's—get really, really scared.
Presence - Sonar - Sound - Source - Diving
"In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern," lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas de Gran Canaria, Spain, told AFP.
"The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen," she added. "It's like an adrenalin shot."
Type - Sonar - Throws - Whales - Balance
One type of sonar in particular throws these whales off balance.
Developed in the 1950s to detect submarines, mid-frequency active sonar (MFAS) is used today in naval patrols and exercises, especially by the United States and its NATO allies.
Ships - Signals - Range - Kilohertz - KHz
Starting around 1960, ships began emitting underwater signals in a range of about 5 kilohertz (kHz).
That is when the mass beaching of beaked whales, especially in the Mediterranean, began.
Mass - Strandings - Place - Time - Place
Between 1960 and 2004, 121 of these so-called "atypical" mass strandings took place, with at least 40 closely linked in time and place with naval activities.
These were not individual strandings of old or sick animals, nor...
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