On land, being serenaded by birds is a familiar morning routine for many people, especially in healthy ecosystems. We often take this dawn chorus for granted, but it's part of a natural soundscape that can have therapeutic effects for humans.
It's also just one example of what — and where — a dawn chorus can be. As a new study off the coast of Western Australia illustrates, the phenomenon also occurs in the ocean, thanks to a variety of symphonic fish that play the role of birds.
Led by researchers from Australia's Curtin University, the study adds to a murky scientific sense of what life sounds like in healthy underwater habitats. Scientists have known for decades that fish "sing," often with the same crepuscular tendencies of birds. Yet we still have much to learn about those songs; aside from their distinct musical style, they can shed vital light on the way marine ecosystems work.
"I've been listening to fish squawks, burble and pops for nearly 30 years now, and they still amaze me with their variety," study co-author Robert McCauley tells New Scientist. "We are only just beginning to appreciate the complexity involved and still have only a crude idea of what is going on in the undersea acoustic environment."
As with birds, a fish chorus develops when lots of individual vocalizations start to overlap. To demystify these performances — including their timing, frequency and what they reveal about the singers — the Curtin researchers recorded fish choruses near reefs off Western Australia over 18 months. They identified seven different choruses, reporting distinct daily patterns "associated with sunrise or sunset and, in some cases, both." The recording below features three of those choruses:
The study's authors are careful about identifying species behind the songs, which is understandably difficult, but they do speculate about several of the singers. The low "foghorn" call comes from a Protonibea diacanthus, also known as a blackspotted croaker, Greta Keenan reports in New Scientist, while a species of Terapontid makes a sound that researcher Miles Parsons likens to the buzzer in the board game "Operation." The clip also includes a quieter "ba-ba-ba" chorus attributed to batfish.
The recordings were made at two sites off Port Hedland, Western Australia, in coastal waters measuring 8 meters (26 feet) and 18 meters (59 feet) deep. Multiple choruses didn't always occur at the same time and place, but when they did, some overlapped and some seemed to stand out by altering their timing or frequency.
"Some pairs of choruses present on the same day exhibited various combinations of temporal and frequency partitioning," the researchers write, "while others displayed predominant overlap in both spaces."
Fish vocalize for a wide range of reasons, from attracting mates and hunting in groups to scaring predators and defending territory. Many species produce sound by drumming on their swim bladders with a "sonic muscle," although fish songs can also come from stridulation — a rubbing motion similar to how crickets make sounds — or from the hydrodynamic sound caused by changing direction while swimming.
These recordings are part of a larger quest to understand reef ecosystems by listening to their inhabitants. Earlier this year, for example, several of the same researchers published another study in the ICES Journal of Marine Science describing nine chorus types in the waters of Darwin Harbor off Australia's northern coast.
Beyond dawn and dusk choruses, newer studies are also painting a more complex picture of when and why fish sing, Parsons tells MNN via email. "As we pick up more recording forms around Australia, we've been getting more and more data with choruses showing up throughout the day as well," he writes. "We also have sites where some of these choruses appear for a short time and then disappear, only to come back the next season/migration/whatever the driving cycle is."
Listening to fish choruses can reveal a wealth of details about the fish, the researchers note, such as location, body size, group size, health status and behavioral patterns. And as past studies have shown, the noise of reef habitats also provides broader benefits, helping baby corals, crustaceans and other animals locate the reefs where they'll settle down and grow up. Many reef dwellers are born in open water, and their larvae must use sensory clues to find their future homes.
We still barely understand fish choruses, or the mysterious underwater worlds that inspire them. But like the dawn chorus on land, we know this is the soundtrack of a normal, healthy and biodiverse ecosystem, even if it sounds a little strange to terrestrial ears like ours. And given the threats facing reef habitats around the world — from pollution and ship traffic to ocean acidification and warming seawater — these choruses could hold vital clues for conservation of ocean life.
So, in hopes of helping fish convey the hidden majesty of their marine environments, here's a rough translation of what sea creatures are presumably singing: