Man standing beside a seawall, in front of an ocean

Scientists eavesdropping on fish to fathom their underwater secrets

Canada’s National Observer, Local Journalism Initiative Reporter

New technology is allowing researchers to covertly monitor, record and identify the sounds fish make underwater to try to unravel their deepest secrets. 

Researcher Xavier Mouy, a recent PhD graduate at the University of Victoria, and his colleagues have devised a relatively low-cost portable audio-visual system that surreptitiously records the surprising range of acoustics fish produce, but more importantly, pinpoints what creature makes which sound. 

Being able to do so is akin to identifying who is attending a noisy party in a dark room, said Mouy, with important outcomes for scientific monitoring, fisheries and conservation in marine environments. 

It’s no secret that fish as a whole make a bunch of different noises, like hums, clicks, grunts and even farts for breeding, feeding and protecting territory. But there are huge gaps in scientific understanding around the vocal repertoire of individual fish, he said. 

“If you tell people that you use acoustics as a new way to detect fish in the ocean, that’s not exactly groundbreaking,” Mouy told Canada’s National Observer.

“We realized we had to go deeper to know which fish is present, and potentially in the future, how many.” 

Sound, which travels quickly and clearly in water, is an important form of communication for ocean creatures that may not be able to rely on what they can see in aquatic surroundings that often have little or no light, said Mouy, who now works with the National Oceanic and Atmospheric Administration (NOAA) in the U.S. 

Using underwater hydrophones to track, record and study whales is a long-standing practice because they are large, charismatic animals that are more easily identified, Mouy said. It was while researching marine mammals that his interest was piqued by the mysterious racket being generated by fish.

“When I was working in coastal British Columbia, I could hear so many fish all over and all year round, but nobody could tell me what species they were,” Mouy said. 

“So, I decided to develop instrumentation to figure it out.”

Mouy devised three types of mobile systems for use in different habitats equipped with multiple cameras and hydrophones. The acoustics triangulate the location of a fish making sounds and match it with the video data to confirm the species. 

After testing the technology at four locations in waters around southern Vancouver Island, the team identified sounds made by three fish species — the quillback rockfish, the copper rockfish and lingcod — which hadn’t been identified as soniferous, (noisemaking), before.

It’s an exciting find with big implications, Mouy said. 

The quillback is a threatened species and knowing the noises it makes will go a long way to determining what habitat it prefers and thrives in. Also, B.C. has more than 160 rockfish conservation areas, and as the acoustic catalogue for various fish improves, so can scientific evaluation of whether a protected area is meeting its objectives or not, he said. 

Snagging the sounds lingcod produce is also a great catch, he added. 

“It’s a species important for fisheries, so it will likely be useful for management or conservation.” 

The new sounds will soon be added to a publicly accessible “acoustic library” developed by other researchers at UVic called FishSounds.net.  

This Sounds Fishy : Xavier Mouy

The acoustic fish surveillance system he designed has some advantages over other research methods, Mouy noted.

Recordings of specific species can be done in tanks, but fish often don’t vocalize in captivity, and if they do, it isn’t necessarily representative of the types of sound they might make in natural environments, Mouy said. Plus, the quality of acoustics recorded in a tank is poor, he added. 

“It’s distorted because the sound bounces on the walls. It’s like you would record someone in a church, it just wouldn’t sound right.” 

Using the portable arrays, some of which can be deployed for two weeks at a time, is also more effective than costly and infrequent diver-based surveys typically used to monitor fish populations, he said. 

Along with his research, Mouy has published the building instructions for the systems and made all related materials and processing software open source, so other scientists can add to and improve his work and further contribute to global research on fish acoustics. 

“I want to avoid that someone has to reinvent the wheel,” he said. 

“If we want fish acoustics to be really useful, we all really need to share and work as a team and identify these sounds worldwide.” 

Top image credit: Scientist Xavier Mouy has created a practical surveillance system that not only captures fish sounds, but identifies the species that make them. – Photo courtesy Xavier Mouy

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