The year 2020, marked by the Covid-19 pandemic, brought an unexpected silence to the world's oceans. This rare moment of tranquility revealed a thriving underwater soundscape, challenging our long-held belief that the ocean was a silent realm.
The Symphony of the Sea
Crackles, snaps, pops, and clicks—these are the building blocks of an aquatic orchestra. Marine biologist Steve Simpson describes it as "an orchestra of thousands of instruments playing simultaneously."
For years, we thought the ocean's silence was a limitation of our human ears. But with the invention of hydrophones, we discovered a whole new world of marine sounds. From the deep sound channel of whales to the snapping shrimp's loud "crack," the ocean is alive with noise.
The Impact of Human Noise
As human-made sounds have increased underwater, crucial animal behaviors like communication, breeding, and feeding have been disrupted. Scientists have been exploring ways to quiet the seas to understand the effects of noise on marine life.
Then, the pandemic hit, and nature provided a unique experiment. With shipping and boating at a standstill, the ocean's natural soundscape emerged, offering a glimpse into a world without human-induced noise pollution.
A Global Experiment
Peter Tyak, a professor of Marine Mammal Biology, was part of the International Quiet Ocean Experiment (IQOE). The idea was simple: instead of adding noise, reduce it to see the impact. In 2020, Covid-19 did just that, leading to a significant decrease in global maritime trade and marine traffic.
This natural experiment allowed scientists to study the effects of sound on marine life. Using 200 ocean hydrophones, they listened to the ocean's soundscape before, during, and after lockdown.
The Results
In New Zealand, when boat traffic in the Hauraki Gulf Marine Park stopped, underwater noise dropped dramatically. This allowed the communication ranges of fish and dolphins to expand, with dolphins' calls traveling up to 1 mile further.
Miles Parsons, a researcher at the Australian Institute of Marine Science, emphasizes the importance of sound for marine animals. "Sound is their primary modality for communication, foraging, and reproduction."
A Noisy Ocean
Unfortunately, the ocean is getting noisier due to human activity and climate change. The growth of global shipping and the degradation of ocean ecosystems have contributed to this increase in noise. About 90% of consumer goods are transported by sea, and the constant movement of container ships adds to the underwater din.
Steve Simpson explains that the ocean's soundscape has changed significantly since preindustrial times. "Now, we have the anthrophony—the sound of motorboats on coral reefs—added to the biophony and geophony."
This human-made noise can mask animal sounds, just as it would above the surface. It's like trying to have a conversation in a crowded bar, Parsons says.
The Effects on Marine Life
Studies have shown that increased ship noise affects the behavior of humpback whales, causing them to feed less frequently and at shallower depths. Migrating humpback whales spend more time underwater and extend their dive durations when vessels are nearby. Even calf pods are more sensitive to vessel presence.
Military sonar has also been linked to whale strandings, with beaked whales showing injuries similar to decompression sickness and acoustic trauma. Just like humans, whales can suffer from chronic stress in areas with heavy noise pollution, which can shorten their lifespans and reduce reproductive success.
Restoring the Ocean with Sound
Understanding how marine life uses sound has led to innovative restoration techniques. Scientists are using underwater speakers to play recordings of healthy reef soundscapes, attracting fish and other marine life back to damaged reefs. This helps accelerate the recovery of these vibrant ecosystems.
The IQOE has also led to the establishment of World Ocean Passive Acoustics Monitoring (WOPAM) Day, an annual initiative started by Parsons and Simpson. It's a global event where people share their recordings and the joy of listening to the ocean.
"It's like eavesdropping on another universe and sharing it with the world," Simpson says.
Further Reading
- The Mysterious World of Fish Communication
- The Scientists Learning to Speak Whale
- The People Eavesdropping on the Ocean
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