The last several decades have seen an explosive uptick in the number of mass stranding events (MSEs) involving certain types of whales, prompting researchers to embark on a perennial quest to determine the cause and present possible solutions.
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A whole host of theories have been brought to the table in recent years, including the belief that climate change-induced warming waters were to blame, the notion that shifts in Earth’s magnetic field confuse the animals, and the idea that naval sonar was driving the creatures insane. But with so many ideas in play, where do we even begin?
Curiously, the naval sonar theory comes up more often than some would like to admit, and it appears to be the epicenter of a new study published just this week in the journal Proceedings of the Royal Society B.
As noted in the study, MSEs were rather infrequent before the introduction of naval mid-frequency active sonar in the 1960s, a correlation that’s difficult to ignore given the evidence that appears to support it. But while many studies have pointed the finger at naval sonar as a potential cause for MSEs, most have failed to explain how and why; that’s where the new paper comes in.
The researchers of the new paper suggest that beaked whales are incredibly sensitive to mid-frequency active sonar and that it impacts the marine animals in undesirable ways. More specifically, they become scared by the sounds and attempt to get away, sometimes rushing to the surface and coming down with decompression sickness.
"In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern," elucidated study lead author Yara Bernaldo de Quiros from the University of Las Palmas de Gran Canaria. "The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen. It’s like an adrenalin shot."
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When whales become stranded on the beach, experts roll in to perform necropsies on the animals to discern their cause of death. Many times the animals seem perfectly healthy at first glance, but closer examinations uncovered nitrogen gas bubbles in the blood veins and damage to vital organs, denoting all the tell-tale symptoms of decompression sickness.
The researchers also go on to cite the Canary Island moratorium, in which a study published in Nature in 2003 placed a magnifying glass on the potential link between naval sonar and whale strandings; consequently, Spain forbade naval exercises in the region in 2004. MSEs were reportedly somewhat frequent before the moratorium but stopped in their entirety afterward.
"Up until then, the Canaries were a hotspot for this kind of 'atypical' strandings," Bernaldo de Quiros said. "Since the moratorium, none have occurred."
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With many whale species recognized by the International Union for the Conservation of Nature (IUCN) as endangered or vulnerable, the study brings a significant problem into the light. It seems unlikely that naval sonar will be replaced by other technologies anytime soon, but perhaps the findings will help facilitate forward-thinking research for the sake of the whales that inhabit our oceans.