Scientists have long known that some beaked whales strand themselves and die in distress after being exposed to marine sonar You know why: The huge marine mammals suffer from decompression sickness like the divers.
The statement, published Wednesday by 21 experts in the journal Proceedings B of the Royal Society, seems implausible.
Millions of years of evolution have made whales into perfectly calibrated dive machines that dive miles for miles beneath the surface, searching for food in the deeps.
The heart rate slows down, blood flow is limited and oxygen consumption is reduced.
How could the ocean's most experienced deep-sea diver explode with nitrogen bubbles poisoning his veins, like a diver diving too fast to the surface?
Short answer: Beaked whales ̵
"In the presence of sonar, they become stressed and swim energetically away from the sound source and change their diving pattern," writes lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas in Gran Canaria, Spain AFP.
"The stress response thus overrides the immersion reaction, causing the animals to accumulate nitrogen," she added. "It's like an adrenaline shot."
In particular, a type of sonar throws these whales out of balance.
– "Atypical" mass dislocations –
In the 1950s developed for detection of submarines active mid-frequency sonar (MFAS) is now used in naval patrols and exercises, mainly by the United States and its NATO allies.
From 1960 ships emitted underwater signals in a range of approximately 5 kilohertz (kHz).
That was the time The mass occupation of beaked whales, especially in the Mediterranean, began.
Between 1960 and 2004, 121 of these so-called "atypical" mass starvations took place, with at least 40 being temporally and locally linked to naval activities.
These were not individual strandings of old or sick animals or en masse sinking, as was the case in New Zealand last November when more than 200 pilot whales came ashore on the beach within a day or two and no more than a few tens of kilometers apart.
The deadliest episode in 2002 was stranded at 14 during a NATO naval exercise in the Canary Islands over a period of 36 hours.
"Within hours of using the sonar, the animals appeared on the beach," said Bernaldo de Quiros. Outwardly, the whales showed no signs of illness or harm: they had normal body weight and no skin lesions or infections.
Internally it was a different story. Nitrogen gas bubbles filled her veins, and her brain was devastated by bleeding.
Autopsies also damaged other organs as well as the spinal cord and the central nervous system.
– Moratorium of the Canary Islands –
As In altitude sickness, the reactions – in humans and probably also in whales – vary in type and intensity of nitrogen bubbles in the blood.
A 2003 study in Nature on the possible association between sonar and whale deaths led to a ban on Spain's naval exercises in the Canary Islands in 2004.
"Until then, the Canaries were a hotspot for this type of "atypical" strandings, "said Bernaldo de Quiros. "None has occurred since the moratorium."
The authors demanded that similar bans be extended to other areas where endangered whales are accumulating.
The Cuvier grows up to seven meters high and eats mainly deep-sea water and fish. His upturned mouth gives the impression of a permanent smile.
The whale is classified as "susceptible" to the IUCN endangered species and is believed to have a world population of 5,000 to 7,000.
Other threats include ship attacks, marine pollution and habitat displacement as a result of climate change.
© 2019 AFP