With the constant churn of freighter propellers, the percussive thump of oil and gas exploration and the underwater din of military testing, ocean noise levels have become unbearable for some sea mammals.
Contrary to the image of a distant and silent world under the sea, underwater sound intensity has on average soared 20 decibels over the past 50 years, with devastating consequences for wildlife.
“Sound is what cetaceans [large aquatic mammals like whales and dolphins] communicate with. This is how they perceive their environment. For them, hearing is as important as vision is for us,” said Mark Simmonds, the international director of science at the Whale and Dolphin Conservation Society (WDCS).
“If there is too much noise, they probably can’t communicate that well,” he said late last month on the sidelines of an international conference on migratory species in Bergen, on Norway’s southwestern coast.
A harmful effect of this acoustic “fog” is that it impairs the ability of cetaceans, which in good conditions can communicate over a distance of dozens of kilometers, to orient themselves, find food and reproduce.
Basic small boat traffic traveling at slow speeds through shallow waters can be enough to cut the reach of sounds from a bottlenose dolphin, for instance, by 26 percent, and in the case of pilot whales by 58 percent, according to a recent study.
Nicolas Entrup, who works with the non-governmental organizations Ocean Care and the Natural Resources Defense Council, said the ocean is in the process of becoming for sea mammals what night clubs are for humans.
“You might cope with it for a while, but you can’t live there,” he said.
“Imagine a situation where you can’t communicate with your family, where you have to scream constantly,” he said.
Oceans are vast and animals that are bothered by rising noise levels can of course move on, but it can be challenging to find and adapt to a whole new habitat.
The problem is especially dire in the Arctic, where, as the polar ice cap melts, humans are leaving an ever bigger sound footprint as they stake out new shipping routes and look for oil and gas.
“Narwals, for example, have a narrowly defined habitat,” Simmonds said. “They are very adapted to that cold environment. If it gets too noisy, where will they go?”
The same problem applies to the highly sound-sensitive beluga, or white whale, that migrates to Canada’s northern shores.
These mammals, which are capable of detecting ships 30km away, will struggle to maintain their migration route through the narrow straits circling Baffin Island as shipping in the area risks increasing sharply to accommodate a new large-scale mining project.
“We simply don’t know how certain species will adapt, or even if they will adapt at all,” Simmonds said.
In some cases, human-produced commotion is fatal.
The use of anti-submarine sonars is, for instance, suspected of causing the mass-beaching of whales: In 2002, about 15 beaked whales perished in the Canary Islands after a NATO exercise.
“Since we’re talking about military matters, there is no transparent information available and we know very little of the real scope of the problem,” Entrup said.
Other threats include seismic exploration for oil and gas, which involves the use of air canons to induce tremors in the seabed aimed at detecting the potential riches hidden below.