https://phys.org/news/2018-11-piranha-bark.html

Next month, Rodney Rountree, "The Fish Listener," will talk about his work with Francis Juanes of the University of Victoria, to document calls made by fish in the Pacaya-Samiria National Reserve in Peru in a presentation at the Acoustical Society of America's 176th Meeting, held in conjunction with the Canadian Acoustical Association's 2018 Acoustics Week in Canada, Nov. 5-9 in Victoria, British Columbia. These calls may be useful for tracking piranha populations through passive acoustic monitoring.

"In the Amazon, most of the habitats are very turbid so you usually can't put cameras down and watch the behavior. The only way to survey fish is to catch them," Rountree said. "Passive acoustics lets you potentially locate fish just by their sounds."