For centuries we have known that fish make sounds, but we have almost always ignored them. Not because they weren’t important, but because actually listening to them was complicated. In a coral reef the sea is never silent: dozens of species coexist producing short, close together, often overlapping noises. Understanding who “speaks” and when, until recently, was an almost unsolvable technical puzzle.
Today this scenario has changed radically. A group of scientists has developed and tested a new combination of underwater audio and video recording, managing to positively identify the sounds produced by 46 species of fish in their natural environment. This is the largest collection of wild fish sounds ever recorded. The device, described in the scientific journal Methods in Ecology and Evolutioncan extract individual acoustic signals from extremely complex underwater recordings and precisely determine which fish made each sound.
UPAC-360°
The heart of this innovation is called UPAC-360°, an acronym for Underwater Passive Acoustic Camera omni-directional. This tool records audio and video continuously and in all directions, creating a three-dimensional map of the sound. Unlike studies on whales and dolphins – animals that emit powerful calls, easily attributable to a few individuals – fish produce short, weak and frequent sounds, often overlapping with each other.
The difficulty is increased by a surprising detail: many fish do not move at all while making a sound, a bit like underwater ventriloquists. This makes it almost impossible, with the naked eye or with a simple microphone, to understand who is “talking”.
UPAC-360° overcomes this limit. The system identifies the direction from which the sound comes, isolates the corresponding audio segment and matches it with the video images coming from that same point. Even when dozens of fish swim in the scene at the same time, the technology manages to locate the exact position of the single specimen that produced the sound. The data is then transformed into an acoustic map, overlaid on the video, allowing each noise to be attributed to a precise species.
According to Aaron Rice, ecologist at Cornell University and co-author of the study, the result surprised the researchers themselves:
We were shocked at how many fish we were able to record and identify in such a short time.
The value of this discovery goes far beyond scientific curiosity. Currently, over 4,000 fish species are classified by the IUCN as vulnerable, endangered or critically endangered. Analyzing their sounds allows scientists to understand where they live, how populations change over time, when they are most active and what behaviors make them more exposed to predators.
During the study, divers placed the camera, surrounded by four hydrophones, at 13 coral reefs around Curaçao, in the Caribbean. In just 11 days of recording, the system identified the sounds of 46 species, none of which had public recordings of vocalizations in the wild available up to that point.
Ecologist Audrey Looby, of the University of Victoria in British Columbia, who was not involved in the study, underlined the importance of the result. After analyzing 150 years of research on fish sounds, he found that fewer than 3 percent of the approximately 35,000 known species have ever been recorded. From this work, FishSounds.net was born, a global database that collects the vocalizations of the 1,258 species documented so far. According to Looby, sound production in fish is probably much more widespread and crucial to ecosystems than has always been thought, but the right tools to prove it were lacking.
The current limitations and future of fish sound research
Despite the extraordinary results, the technology still has limitations. The UPAC-360° must be positioned manually by divers, so recordings stop at around 45 meters depth. Additionally, the video system requires natural light, making species identification impossible at night. For this reason, the sounds of fish that live in deeper water or that are active in the dark remain, for now, a mystery.
The research team is already working on new versions of the device, designed to operate at greater depths and in low light conditions. Meanwhile, the entire collection of collected fish sounds is available for free at fisheyecollaborative.org/library, giving scientists and enthusiasts a valuable tool to better understand the life hidden beneath the surface of the sea.
As Aaron Rice pointed out, we are continually discovering elements that force us to rethink the way we imagine fish and their role in marine ecosystems. And, perhaps for the first time, we are really starting to listen to them.
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