Fish are Loud
Under the ocean, there is a cacophony of sounds, but it’s not just boats and mammals creating the din. Fish are also noisy — as noisy as birds. Unlike birds, fish don’t sing or create melodies. Their sounds resemble drones, creaks, croaks, drums, and even sad trombones. Reef fish are the most likely to vocalize. They do so by oscillating their swim bladders or, like crickets, rubbing together the bones of their pectoral girdles (the part of the skeleton attached to the pectoral fins). Larval fish get caught in ocean currents, but when they become juveniles and need to settle down, they do so by listening for the sound of a reef.
“They will sometimes make a chorus. These incredible loud sounds that dominate the environment,” says Ana Širović, who runs the Marine Bioacoustics Lab at the Scripps Institute of Oceanography in San Diego. Think of it like fans doing the wave at a sports stadium, except it’s fish calling up and down the coast. “You can get very strong daily cycles at sunrise and sunset,” Širović says.
Some fish make noises by emitting air bubbles from the anus , others by using plates on their heads to snap. Researchers believe that fish may be using sound to lure mates or to deter other animals from encroaching on their territory. These calls can be heard from a distance of up to 330 feet — but limited visibility means that it’s almost impossible to locate the source of a call unless the fish is right in front of you. The result is that although scientists have identified hundreds of species of fish with unique sounds, that’s only a small portion of fish noise in the ocean. To better match fish with their calls, Širović has recently partnered with biophysicist Jules Jaffe, whose lab in La Jolla, California, specializes in creating underwater imaging systems. Their research project uses an undersea microphone to determine the locations of interesting sounds, and soon they’ll deploy an array of 360-degree cameras to focus on these areas. “The general sound of the habitat is important to new recruits,” Širović says. Better classifying fish noise will ultimately help researchers to judge, much as the fish themselves do, whether they are listening to a healthy ocean ecosystem. “It’s hard for us to imagine,” Širović says. On land, vision is our most important sense. But the ocean is “a world where your primary cue to everything in life is sound.”