Scientists have long known that some beaks boast and die in agony after exposure to marine sonar, and now they know why: giant marine mammals suffer from decompression sickness, like scuba divers.
At first glance, the explanation given on Wednesday by 21 experts in Proceedings of the Royal Society B seems implausible
Millions of years of evolution have turned whales into perfectly calibrated diving machines, which are immersed in kilometers (miles) from the surface for several hours in a row, getting food in the ink depths.
Heart rate slows down, blood flow is limited, oxygen remains.
So, how could the most advanced deep-sea diver of the ocean end up with nitrogen bubbles that poison his veins, like a novice scuba diver climbing too fast to the surface?
The short answer is: the whale's beak — especially one species known as the Cuvier — is very scared.
“In the presence of sonar, they are stressed and float away from the sound source, changing the immersion pattern,” says lead author Yara Bernaldo de Quiros, a researcher at the Animal Health Institute of the University of Las Palmas de Gran Canaria, Spain. told AFP.
“In other words, the stress response cancels the diving response, which causes animals to accumulate nitrogen,” she added. "It's like a shot of adrenaline."
In particular, one type of sonar knocks these whales off balance.
Developed in the 1950s to detect submarines, mid-range active sonar (MFAS) is used today in naval patrols and exercises, especially by the United States and its NATO allies.
Starting around 1960, ships began to emit underwater signals in the range of about 5 kilohertz (kHz).
It was then that began mass swimming beaks, especially in the Mediterranean.
In the period from 1960 to 2004, 121 of these so-called “atypical” mass clashes occurred, at least 40 of which were closely related in time and place to naval activities.
They were not separate groups of old or sick animals, but also groups similar to those that were in New Zealand last November, when more than 200 pilot whales climbed ashore together.
Most likely, a handful or several beaks of the roll will fly to the shore within a day or two, and at a distance of no more than a few tens of kilometers.
The most deadly episode in 2002 was 14 people caught up in the Canary Islands for 36 hours during NATO naval exercises.
“A few hours after the deployment of the sonar, the animals began to appear on the beach,” said Bernaldo de Quiroz.
Externally, the whales had no signs of disease or damage: they had a normal body weight, and there were no skin lesions or infections.
Internally, it was a different story. Nitrogen gas bubbles filled the veins, and their brains were exhausted by bleeding.
An autopsy also revealed damage to other organs, as well as to the spinal cord and central nervous system.
Canary Islands Moratorium
As in the case of altitude sickness, the reactions — in humans and, perhaps, in whales — to nitrogen bubbles in the blood vary in type and intensity.
2003 study in Nature Because of the possible link between the death of sonar and the whale in 2004, Spain banned such naval exercises around the Canary Islands.
“Before this, the Canary Islands were a hot spot for this kind of“ atypical ”strands,” said Bernaldo de Quiros. “Nothing happened since the moratorium.”
The authors called for the extension of similar bans to other regions where it is known that whales at risk are going.
The Cuvier grows to seven meters (23 feet) and dines mainly on deep-sea squid and fish. His upturned mouth gives the impression of a constant smile.
The whale is listed as vulnerable in the IUCN Red List of Endangered Species, and its global population is estimated to be from 5,000 to 7,000 people.
Other threats include impacts from ships, ocean pollution and habitat displacement caused by climate change.
The study shows that whales dive deeper and longer when exposed to man-made sonar
Advances in research on the effects of antisubmarine sonar on beaks, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or… .1098 / rspb.2018.2533