Sonar From NATO Naval Exercise Suspected in Scottish Whale Strandings
'Exercise Joint Warrior', a twice-yearly NATO war games event held around northern Scotland may be responsible for a spate of whale strandings during October, according to the Scottish Marine Animal Strandings Scheme (SMASS). Two of the animals may have died as a result of decompression sickness (DCS) brought on by trying to escape the noise of military sonar.
Necropsies carried out on two Sowerby's beaked whales (Mesoplodon bidens) by the National Museums of Scotland in Edinburgh, discovered the presence of 'an unusually high number and distribution of gas bubbles throughout the tissues; especially lung, liver and intestinal mesentery' (a membrane which attaches the intestine to the abdominal wall and assists in a variety of functions), according to a report posted on the SMASS Facebook page.
Although the two sub-adult males had suffered 'significant trauma from the stranding process', they were otherwise determined to be healthy and 'in reasonable body condition'. Three northern bottlenose whales (Hyperoodon ampullatus) found in other locations during the same time period were too decomposed to determine an accurate cause of death.
Gas bubbles are commonly found in the tissues of dead cetaceans during post-mortem examinations, caused by natural decomposition, or emphysema (damage to the air sacs in the lungs) caused by the stranding. A large number of bubbles, however, especially in deep-diving species such as the Sowerby's beaked whales stranded in Lothian, maybe 'suggestive of nitrogen emboli and decompression sickness'.
'Given how sensitive beaked whales are to underwater noise, specifically naval sonar, we have to consider noise-mediated DCS as a possible cause for these two strandings,' states the SMASS report. 'We are therefore in the process of trying to find data on sources of noise in this region, including putting a request for activity logs to the MOD following the recent Joint Warrior naval exercises.'
Scientists from the Hebridean Whale and Dolphin Trust (HWDT) monitor the twice-yearly wargames to assess how they may impact the cetacean population in the surrounding areas. Since whales, dolphins and porpoises communicate, navigate and hunt through echolocation – the biological form of sonar – the constant use of sonar by the military is thought to detrimentally impact the animals' behaviour.
The HWDT conducted acoustic surveys from its research vessel Silurian, used during the filming of the BBC's Blue Planet series, hosted by Sir David Attenborough. The team covered 550 nautical miles and collected over 85 hours of acoustic recordings during Exercise Joint Warrior, in which 28 warships, two submarines and more than 80 aircraft participated.
'We heard sonar consistently throughout the next four days, some of which we could hear through the headphones without even putting them on,' the HWDT reported. 'We recorded military sonar on 14 per cent of the track lines conducted on the survey and dolphins whistles on 50 per cent. The hydrophone also picked up over 250 harbour porpoise, with over 1380 individual clicks. Five species of marine mammals were visually recorded including harbour porpoise, common dolphins, minke whales and grey and common seals.'
The use of sonar during military exercises has long been thought to be responsible for cetacean strandings, including the 2018 deaths of more than 90 individuals from different species found stranded in Scotland, Iceland and Ireland. A 2017 study in California also found that Cuvier's beaked whales were diving far deeper and for far longer to avoid military sonar than their regular behaviour would suggest, making them susceptible to decompression sickness once they surfaced.
Following the exercise, the UK's Ministry of Defence (MoD) said that the military was doing all it can to protect marine life from trauma caused by the use of sonar.
'The MoD takes its environmental responsibilities very seriously; environmental impacts are always considered in the planning of military exercises,' said an MoD spokesperson. 'Environmental Impact Assessments have been produced and findings implemented where required, such as for the use of active sonar and live weapons.'