Amazonian lakes and rivers don't always have the clearest of water, so how do biologists know if piranhas are present? They can always try fishing for the things, although according to new research, listening for their "barks" may be a better way to go.
Along with various other species of fish, piranhas are able to make several types of noises by contracting muscles near their gas bladders. Although these so-called barks have previously been recorded in lab settings, American marine biologist Rodney Rountree (aka "The Fish Listener") set out to record and then listen for them in Peru's Pacaya-Samiria National Reserve.
Working with Prof. Francis Juanes of Canada's University of Victoria, he started by catching over 550 fish representing at least 70 species, and gently holding them underwater next to a hydrophone. This resulted in a database of bark recordings, including examples from four types of piranhas. Utilizing statistical analysis, he was able to determine which bark patterns were made by which types.
Rountree subsequently made underwater "soundscape" recordings at 22 sites within the reserve, and could hear those distinctive barks in areas where piranhas were already known to be feeding. Additionally, he detected the startled calls made by catfish and other species, which were likely a result of those fish being nipped by the piranhas.
He now plans on conducting further research in order to better differentiate between the barks of various piranha species, and to compensate for factors that affect the sound of those barks, such as fish size and ambient water temperature. Ultimately, he hopes that biologists will be able to listen for piranhas simply by lowering hydrophones down into the water from boats – an easier and less invasive approach than physically capturing the fish.
"A lot of times, the most difficult thing is finding where they are," he says. "So any tool that helps you find the fish is very helpful."
Rountree will be presenting the results of his study this week at the Acoustical Society of America's 176th Meeting in Victoria, Canada.
Source: Acoustical Society of America via EurekAlert
