The background volume in the oceans has roughly doubled in intensity each decade since the 1950s, due to more shipping. Meanwhile, military sonar devices blast out acoustic waves, as do the underwater airguns used in seismic surveys for oil and gas deposits.
In noisy seas, whales and dolphins have trouble communicating with each other; some sing or whistle louder, while others give up and fall silent. Sonar seems to disorientate these animals, making them more likely to ascend too quickly and suffer decompression sickness.
In lab studies, scallop larvae exposed to noise pollution develop deformed bodies, fish are deafened, and jellyfish, squid and octopuses suffer damage to their balance organs (‘statocysts’), which impairs their sense of orientation. Airguns can also kill tiny zooplankton from more than a kilometre away.
As with plastic pollution, it’s not yet clear how noise pollution impacts entire populations or ecosystems. To find out more, scientists make the most of opportunities when shipping stops and the oceans quieten – such as during the coronavirus pandemic, when hydrophones registered reduced noise levels as far as 3,000m underwater.
We don’t yet know how marine life has responded to this hush, but a long-term study of right whales in Canada’s Bay of Fundy offers a hint. The study found lower levels of stress hormones in the whales’ faeces when shipping was halted following the 9/11 attacks. As the noise ramped back up, the whales got stressed again.
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