A team of researchers from the Centre for Marine and Science Technology in Perth, Australia have recorded an orchestra under the sea. This extensive study used a pair of continuous recording devices to reveal the fishy equivalent of the birds’ “dawn chorus.”

The first surprise for many may be the news that fish even make noise, but a variety of species are able to display a range of noises at a variety of frequencies. This creates an amazing combination of sounds in the underwater world.

“I’ve been listening to fish squawks, burble and pops for nearly 30 years now, and they still amaze me with their variety,” said researcher Robert McCauley.

Previous work has shown that fish make noises for all kinds of reasons. The sounds fish make can be used to attract a mate or even to repel a rival, making them important elements of reproduction and territory defence. Communication with sound is also essential for certain feeding behaviours such as hunting in groups.

All together now

The team from Perth recorded the sounds using two sea-noise recorders. They wanted to understand more about the times when the fish ‘chorus’, creating sounds that overlap with other fish vocalisations in the same vicinity.

The first recorder was submerged in 10 metres of water and positioned just a few hundred metres from the shore. The second logger was situated under 18 metres of water and 20km out to sea. The machines were calibrated carefully to account for the continuous low levels of sea noise, allowing the recorders better range to capture any noises made by fish.

After recording for 5 minutes of every 15 minutes of the day for 18 months, there was a lot of data to analyse. With sounds ranging from passing boats to humpback whales it was a great undertaking to separate the sounds made by chorusing fish.

The choruses were predominantly recorded between early spring and late summer, with peaks of noise at dawn and dusk. The researches classified all of the choruses into seven different types that each had defining characteristics. To listen to a recording, click the play button on the featured image above.

By understanding the patterns that are produced by singing groups of fish, scientists hope they can be in a good position to monitor any changes. With noise such an important behaviour, monitoring changes could identify that fish have begun to behave differently, or react badly to environmental stressors.

Underwater noise pollution

One of the problems faced by this team was the amount of human generated noise. At times, it could be difficult for the scientists to even hear the fish due to high levels of boat traffic or machinery use. However, all seven choruses were recorded alongside significant levels of anthropogenic noise, meaning the fish weren’t immediately displaced by it. Measuring the long term impact of continued and increasing levels of human noise and activity will be an important element in the research group’s work in the future.

“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,” said McCauley.

Future work could help to measure and minimise the human impact of underwater noise, particularly at the important times of year when choruses are in full swing.

reference
Parsons, M. J., Salgado Kent, C. P., Recalde-Salas, A., & McCauley, R. D. (2016). Fish choruses off Port Hedland, Western Australia. Bioacoustics, 1-18.
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