Identify a piranha by its bark

The bite of a piranha is much worse than its bark, but it also has uses. A new study of sounds emitted by piranhas in the Amazon shows that their underwater "barking" is an effective tool for identifying different species in murky waters.

Scientists have previously documented several sounds that piranhas emit by contracting muscles near their gas bladders, but these studies were mostly done in the laboratory.

Next month, Rodney Rountree, "The Fish Listener", will speak about his work with Francis Juanes of the University of Victoria, to document the calls made by fish in the Pacaya-Samiria National Reserve in Peru as part of a presentation at the Acoustical Society of America The 176th meeting was held November 5-9 in Victoria, British Columbia, on the occasion of 2018 Canada's Acoustic Week. of the Canadian Audio Association. These calls can be useful for tracking piranha populations through passive acoustic monitoring.

"In the Amazon, most habitats are very turbid, so you usually can not install cameras and observe the behavior, the only way to investigate the fish is to catch them," said Rountree. "Passive acoustics allows you to potentially locate fish only by their sounds."

During routine surveys conducted in the reserve in 2012, Rountree "auditioned" the captured fish by gently placing them under water next to a hydrophone to record any noises. In total, he auditioned over 550 people from at least 70 species of fish, including four types of piranhas. With the help of a statistical analysis, Rountree could differentiate the species of piranhas, even the closest, depending on the type of bark.

Rountree also recorded underwater soundscapes at 22 sites on the reserve. He heard similar piranha barking at places where it was known that piranhas were feeding, as well as scared calls of catfish and other prey. "When piranhas are present and feeding, they bite and bite, so the other fish make a lot of sounds," he said.

How could this be extended to monitor piranhas in the wild? Scientists could potentially deploy hydrophones of small boats to understand how piranhas affect the ecosystem Such studies could also help us understand how fish navigate their natural soundscape and whether human activity creates disturbances .

However, further studies will be needed to determine the best ways to differentiate piranha species and check the range of barks produced by each type. Factors such as the ambient temperature of the water and the size of the fish can affect the sounds.

As a simple, non-invasive method, passive acoustic monitoring could complement or even replace traditional methods of catching fish. "Often the hardest thing is to find where they are," said Rountree. "So any tool that helps you find the fish is very useful."

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More information:
Presentation # 1pAB9, "Sounds of the Amazon: Piranha and Prey", by Rodney A. Rountree and Francis Juanes will take place on Monday, November 5th at 3:30 pm. at Crystal Ballroom (FE), Victoria Conference Center, Victoria, British Columbia, Canada. acousticalsociety.org/asa-meetings/