There has been a perplexing spate of strandings in Europe in the last few weeks, which scientists fear may have been triggered by a sonar anti-submarine exercise called Dynamic Mongoose that took place off the coast of Iceland. The exercise took place in July and within a fortnight there were reports of unusual sightings of whales. Scientists fear that if the NATO test is to blame, the events that followed could be just the tip of the iceberg in what is proving to be a catastrophic event for Europe’s whale populations.

In the past few weeks alone, there have been 29 sightings of beaked whales, an elusive whale species that are rarely seen in the wild. While strandings do sometimes happen as the result of storms and illness, the sudden spike in beaked whales found in shallow waters or on beaches has led marine scientists to believe that a singular cause is to blame.

There were also two deep-sea whale species found on beaches in the United Kingdom within 24 hours of each other. The kind of sonar used by NATO is known to cause decompression sickness in deep-sea whales that causes them to beach themselves, which could explain the quick succession of stranded animals. The illness drives them into shallow waters where they can’t find food and they can become disorientated and starve.

Dutch whale researcher Jeroen Hoekendijk, who has been monitoring whale strandings in the Netherlands, noted in a blog the military’s use of sonar testing in the area.

“On 19 August, the British navy escorted nine Russian naval vessels out of English waters in a combined operation with the Canadian navy and various European countries. The large number of naval vessels were in the area because a large-scale NATO anti-submarine exercise ('Dynamic Mongoose') [which] took place off the coast of Iceland last month," Hoekendijk wrote.

“Research has shown that the military sonar used for this can and has led to mass strandings of beaked whales. It is quite possible that the now stranded animals are also a direct result of such an exercise.”

The concern is supported by previous research published in the journal Proceedings of the Royal Society B, which described how the use of sonar results in nitrogen bubbles forming in the blood of such whale species. This condition is known as the bends in divers, and causes hemorrhaging and vital organ damage in whales. The association of this condition with sonar became apparent after the 1960s when previously rare strandings of beaked whales began happening more often. This was found to be linked to the introduction of a type of sonar called mid-frequency active sonar (MFAS) which was being used by the Navy to detect submarines. MFAS produces an incredibly loud sound which is both alarming and dangerous for marine animals such as whales.