Jacques Cousteau was wrong. The underwater world is anything but silent, although human ears may fail to hear it.
“At the lowest frequencies, the ocean rumbles with Earth’s seismic mumblings: mud slides in subsea canyons; rock groans as mid-ocean ridges spread; undersea volcanoes roar … Wind and wave sound suffuses the ocean … Heavy rain can raise ambient sound levels by 35 decibels.
“Coral reef sound travels dozens of kilometers underwater before it fades. Shrimp snap their claws. Parrotfish teeth crunch through coral as they graze on algae. Fish drum their swim bladders and pop their jaws.”
Sing Like Fish: How Sound Rules Life Under Water by Amorina Kingdon explores the underwater world of sound, pointing out its importance in a space where sight is unreliable due to the lack of light and often-murky water. Sound works differently underwater than it does in air, travelling faster and further. “Depending on its wavelength, it can move differently in shallow water and deep water, and over long distances it can veer and bend, forming silent ‘shadow zones’ or concentrated sound ‘channels’.”
Sound consists of waves of energy, and underwater creatures respond to movement as a sound wave moves through their body, bending the cilia on hair cells, and sending information to the brain. The hair cells in fish are located in fluid-filled canals. Fluid moving in the canals bends the hair cells, pushing against a little stone called an otolith that translates the movement into a nerve impulse. An invertebrate’s hair cells may be on its surface or in organs that sense orientation, balance, and gravity.
Sound enables us to perceive the world around us. For underwater creatures, it enables them to locate prey or a destination, to connect with a mate, or to communicate with an infant or a family group. Fish larvae hatch in shallow water but drift out to sea where they are less vulnerable to predators and stay there until they are big enough to survive in a busy reef community. They rely on sound to find their way back to the reef from which they came.
Gobies, small ray-finned fish, use sight, smell, and sound in the courting process. “The fish were using each sense at a different stage of the dance, at a different range, depending on how that sense best worked underwater. He smelled her and saw her and started grunting. She saw him and moved toward his sound and color change. They then coordinated grunts and nods until they spawned. This complex ballet had a purpose – coordination. Fish don’t have penetrative sex: They release their gametes side by side. And if you’ve ever spilled something in water, especially moving water like a river or an ocean, you know that if you release two things and want them to have any chance of mixing, you need to release them simultaneously.”
One marine researcher studied the sounds employed by Aurora, a female beluga, and Tuvaq, her newborn calf. Tuvaq made his first sounds when he was only an hour old and they gradually increased in volume and variety. In the two hours after his birth, Aurora made a new contact call, repeating it 588 times. She called when Tuvaq made a sound, when she was separated from her calf, or when divers entered the tank. While humans rely on touch to hold their newborns close, Aurora was using sound to stay in touch with her child.
Humpback whales sing, an 8-20-minute sequence of calls that have pattern and rhythm. And they can learn new songs. Whales on the east and west coasts of Australia are separate groups and normally have separate songs. “In 1995, all the eastern Australian singers were crooning the same song. But in 1996, two singers out of the eighty-two recorded as the whales swam northward and then southward, sang a completely different song. When the whales arrived on the breeding grounds in 1997, more than half of the whales had switched to the new song, and three whales sang a mash-up of the old and new. By the end of 1998, all the whales recorded on the Great Barrier Reef sang the new song.” It wasn’t actually a new song. It was the song of the western humpbacks. A small group of whales must have migrated to the east and brought their song with them.
Below the waves, human-generated noise is pervasive and intrusive, consisting of military sonar, seismic activity in the search for oil and gas, the construction and operation of offshore wind farms, and, above all else, shipping. “In 1980 the world’s merchant shipping fleet (meaning all ships, not just containers) numbered just under 700,000. In 2020, it’s more than 2 million … Average ship sound levels have doubled in the ocean every decade from the 1960s through the late 2000s.”
Noise is hard to measure or to regulate. Researchers refer to concentric zones of influence like a bull’s eye around a noise source. In the zone closest to the source, the noise may cause physical damage to an animal’s ears or organs. Further out, it may cause them to change their behaviour or mask the sound of a predator approaching or their mate calling.
In the waters off Denmark, porpoises echolocate in their search for fish amid busy North Sea shipping lanes. A four-day study showed the porpoises spent 59% of their time foraging and were bombarded by noise 17-83% of the time. “During one pass of a ferry, a porpoise stopped foraging while the ferry was still 7 kilometers away, waiting fifteen minutes before it began to hunt again.” Hunting isn’t a luxury for porpoises. If they want to eat, they must hunt and it takes time and calories. “Porpoises’ metabolic needs are high. If they are interrupted twelve times a day for six minutes, that’s a real energy cost.”
“Opinions on how to regulate [underwater noise] may vary, but the science is getting clearer on what to regulate. Sonar, seismic, and pile driving can create dramatic impacts. But globally, noise-wise, shipping is the big one. Naval-architecture redesigns, slowdowns, and shipping-lane planning are useful. But at the end of the day, the culprit is our way of life: oil, consumer goods, even cruise ships. We cannot bemoan the noisy ocean and order all our household goods online.”
Further Information
It’s Time to Turn Down the Sound in Canada’s Oceans [West Coast Environmental Law]
Photo credit: https://www.flickr.com/photos/apmckinlay/22731323539
EcoFriendly West informs and encourages initiatives that support Western Canada’s natural environment through its online publication and the Nature Companion website/app. Like us on Facebook, follow us on Twitter or Mastodon, or subscribe by email.