Thu, Jan 31, 2019 - Page 7 News List

Sonar may cause suicidal behavior in some whales


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 experience decompression sickness, just like scuba divers.

At first blush, the explanation laid out yesterday by 21 experts in the Royal Society journal Proceedings B seems implausible.

Evolution has turned whales into perfectly calibrated diving machines that plunge kilometers below the surface for hours at a stretch, so how could they wind up with nitrogen bubbles poisoning their veins, like a scuba novice rising too quickly to the surface?

The short answer: Beaked whales — especially one species known as Cuvier’s — get really scared.

“In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern,” said lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas de Gran Canaria, Spain.

“The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen,” she added. “It’s like an adrenalin shot.”

One type of sonar in particular throws these whales off-balance.

Developed in the 1950s to detect submarines, mid-frequency active sonar is used today in naval patrols and exercises, especially by the US and its NATO allies.

Starting in about 1960, ships began emitting underwater signals in a range of about 5 kilohertz. That is when the mass beaching of beaked whales began, especially in the Mediterranean Sea.

Between 1960 and 2004, 121 of these “atypical” mass strandings took place, with at least 40 closely linked in time and place with naval activities.

The most deadly episode, in 2002, saw 14 stranded over a 36-hour period in the Canary Islands during a NATO naval exercise.

“Within a few hours of the sonar being deployed, the animals started showing up on the beach,” Bernaldo de Quiros said.

Outwardly, the whales showed no signs of disease or damage, but internally, it was another story. Nitrogen gas bubbles filled their veins and their brains were ravaged by hemorrhaging.

Autopsies also revealed damage to other organs, as well as to the spinal cord and central nervous system.

A 2003 study in Nature on the possible link between sonar and whale deaths led to Spain banning such naval exercises around the Canary Islands in 2004.

“Since the moratorium, none have occurred,” Bernaldo de Quiros said.

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