Researchers from FishEye Collaborative, a conservation-technology nonprofit, Cornell University, and Aalto University have developed a new tool that combines underwater sound recording and 360° video to pinpoint the sounds made by individual fish. The findings are published in the British Ecological Society journal Methods in Ecology and Evolution.
Ecologists use underwater sound recorders to monitor marine environments like coral reefs. These recorders capture dense soundscapes filled with thumps, pops, and snaps from shrimp and fish.
But until now, ecologists have largely been missing the ability to interpret these sounds to a species level because reefs are crowded with individuals from hundreds of species, very few of which have had sounds accurately attributed to them.
"When it comes to identifying sounds, the same biodiversity we aim to protect is also our greatest challenge," explains Dr Marc Dantzker, lead author of the research and Executive Director of FishEye Collaborative. "The diversity of fish sounds on a coral reef rivals that of birds in a rainforest. In the Caribbean alone, we estimate that over 700 fish species produce sounds."
Now, a newly developed tool that the researchers call an Omnidirectional Underwater Passive Acoustic Camera (UPAC-360) has allowed them to identify the sources of individual sounds and attribute them to 46 fish species from the coral reefs of Curaçao in the Caribbean. More than half of these species were never known to make sound.
The research findings represent the most extensive collection of fish sounds ever published. The growing collection is available to everyone at fisheyecollaborative.org/library .
The researchers say that identified sounds from the library can now be used to automatically train machine learning systems to detect fish species in underwater recordings. This is similar to how birds can be identified through smartphone apps like Cornell Lab of Ornithology's Merlin. "We are a long way from being able to build 'Merlin' for the oceans, but the sounds are useful for scientists and conservationists right away," says Dr Aaron Rice, a senior author of the study.
Dr Dantzker adds, "By identifying which species make which sounds, we're making it possible to decode reef soundscapes, transforming acoustic monitoring into a powerful tool for ocean conservation."
Another strength of the technology is that it can be placed in reefs and left to collect data without the need for a diver or boat to be present.
Dr Rice, a senior author of the study, said: "The fact that our recording system is put out in nature and can record for long periods of time means that we're able to capture species' behaviours and sounds that have never before been witnessed."
Coral reefs are biodiversity hotspots. Shallow tropical coral reefs cover just 0.1% of the ocean floor but support 25% of all marine species. However, they're suffering global declines caused by pressures including climate change, pollution, and unsustainable fishing.
Their imperilled state means that effective monitoring of these ecosystems is more important than ever.
"These reefs are declining rapidly, threatening not just biodiversity, but also the food security and livelihoods of nearly a billion people who depend on them," said Dr Dantzker. "In response, governments and NGOs are investing billions in reef protection and restoration. That's not enough, so we must ensure that we spend these limited funds effectively. We need to track how reefs are responding both to the stressors and the interventions."
Matt Duggan, an author of the study and a Ph.D. candidate working on the project, added, "Until now, the "loudest" species, like dolphins, whales, and snapping shrimp, have overshadowed the many other voices in the sea. By discovering the identity of these hidden voices, acoustics will become a powerful indicator of reef health and resilience and a strategy to monitor wider and deeper."
To create the tool – UPC360, the researchers combined spatial audio recording hydrophones (underwater microphones) with a 360° camera. This technique is used to create virtual reality video content, but it has never been done underwater.
"Spatial Audio lets you hear the direction from which sounds arrive at the camera," explained Dr Dantzker. "When we visualise that sound and lay the picture on top of the 360° image, the result is a video that can reveal which sound came from which fish."
Although the results are the most extensive collection of such fish sounds ever published, they still represent a fraction of the total species in the reef. The researchers say that this technique opens the door to decoding the whole reef. They're expanding the research, growing the library for the Caribbean, and broadening their efforts to other reefs around the world, including Hawai'i and Indonesia, in the coming months.
