Scientists studied the US Pacific territories of the Mariana Archipelago where multinational naval exercises have been held twice a year since 2006.
“From August 2007 to January 2019 there were eight beaked whale stranding events, of which at least three occurred at the same time as major naval anti-submarine operations,” the researchers told the Sun-Herald.
“The likelihood that this occurred by chance is less than one per cent, suggesting that there is a highly significant relationship between anti-submarine sonar and beaked whale strandings on Guam and Saipan.”
The scientists used passive acoustic monitoring to show multiple species of beaked whales occur year-round in the Mariana Archipelago. The monitoring also revealed the use of military anti-submarine sonar on several days per year.
The researchers stressed that strandings of whales and dolphins can be triggered by a range of natural or human causes. The former include bacterial or fungal infections, or natural end of life processes in geriatric animals.
Human-caused strandings may originate from gunshot, entanglement in fishing gear, or trauma from boat hulls and propellers. But there are also cases of other whale species apparently affected by sonar disruption.
“For example, a large group of melon-headed whales stranded and died in Madagascar following seismic exploration there, and the same species was also observed aggregated in a shallow bay off Kauai – an uncommon habitat for the species – during anti-submarine sonar training in Hawaii,” the researchers said.
Other behavioral studies in Norway, the Mediterranean, Bahamas, and off southern California have shown responses of various severity by a wide range of species to sonar.
“While behavioral responses may not result in serious injury or death, there is growing concern that interrupting important behaviour, such as foraging, resting or breeding, or displacement from crucial habitat may present serious, population-level threats,” the scientists said in answers emailed to the Sun-Herald.
Vanessa Pirotta, from Macquarie University’s Marine Predator Research Group, said the study was “a timely reminded of the impacts humans are having acoustically in our marine environment”.
“This paper highlights the impact of anthropogenic noise pollution which is a growing concern as human activity increases in our oceans,” Dr Pirotta said.
“[A]s scientists and conservationists, we need to ensure we take action to reduce this growing threat.”
While it is difficult to know the precise cause of each stranding of whales or dolphins, human-made noise from ships, sonar and underwater construction “reduces the available space for low and high frequency communicators like whales to talk to each other”, she said.
The researchers said that while their study relied on a lengthy period of acoustic recordings, “it would be significantly stronger if we could include the full record of naval activity”.
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.