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In cities, humans during the coronavirus pandemic have offered respite to the natural world, with clear skies and the return of wildlife to waterways. Now, evidence of a drop in underwater noise pollution has led experts to predict that the crisis may also be good news for whales and other marine mammals.
Researchers examining real-time underwater sound signals from deep-sea observatories run by Ocean Networks Canada near the port of Vancouver found a significant drop in low-frequency sound associated with ships.
David Barclay, assistant professor of oceanography at Dalhousie University, who co-authored a paper reviewing the phenomena, examined the power of sound, a way to measure "volume," in the 100 Hz range from two sites, one in the inland and another further from the coast. He found a significant drop in noise from both.
"In general, we know that underwater noise pollution at this frequency has effects on marine mammals," Barclay said. The findings of Barclay and his researchers were first published in The Narwhal.
"There has been a steady drop in noise since January 1, which has meant a change of four or five decibels in the period to April 1," said the scientist.
Economic data from the port showed a drop of around 20% in exports and imports during the same period. The deep ocean site, about 60 km from shipping lanes and in 3,000 meters of water, also showed a drop in average weekly noise of 1.5 decibels, or about a 15% decrease in power, Barclay analyzed. "This gives us an idea of the scale on which this reduction in noise can be observed," he said.
The reduction in ship traffic in the ocean, which Barclay likens to a "giant human experiment," has scientists racing to discover the effect on marine life.
"This is a moment of truth," said Michelle Fournet, a Cornell University marine acoustician who studies humpback whales in southeast Alaska. "We have the opportunity to listen, and that opportunity to listen will not reappear in our lives," he said.
After the terrorist attacks of September 11, when air and ship traffic fell in North America, American researchers were able to study whales in a calmer ocean, and a landmark study concluded that noise pollution from ships was associated with chronic stress in baleen whales.
"We have a generation of humpback whales that have never known a calm ocean," said Fournet, whose work has shown that whales alter their calling behavior in response to a noisy ocean.
Late April generally marks the beginning of the cruise season in Southeast Alaska, with ships docking in Vancouver before heading north. This year the health crisis has stopped them.
"What we know about whales in Southeast Alaska is that when it is loud they call less, and when the boats pass they call less," Fournet said.
"I hope that what we can see is an opportunity for the whales to have more conversation and a more complex conversation."
Ocean scientists around the world, many of whom are unable to do practical work due to the pandemic, are desperate to gather data from this unique opportunity to listen.
Nathan Merchant, a bioacoustics expert at the UK government's Center for Environment, Fisheries and Aquaculture Science (Cefas) in Lowestoft, said: "We are waiting to see what our records say."
Cefas has hydrophones to collect noise data at four sites: two in the North Sea, one in Plymouth, and one near Bangor.
Merchant said there have been international efforts to coordinate underwater noise monitoring work.
"We are going to see how the coronavirus is affecting underwater noise across Europe, so this work outside of Canada will be the first of many," he said.
He and his colleagues have long been discussing how they could conduct an experiment to make the ocean calmer, in order to find out what benefit it would have.
“We have this natural experiment underway. Of course, it is a terrible crisis, but we could go ahead and look at the data to find out what effect it is having. "