May 22 (UPI) -- European spiny lobsters make surprisingly loud noises by rubbing their antennas against a rough spot beneath their eyes. The sound, known as antennal rasps, can be heard more than 1.8 miles away, according to a new study published this week in the journal Scientific Reports,
Scientists hope the study of spiny lobster noises can aid conservation efforts. Due to overfishing, the European spiny lobster is classified as "vulnerable" on the Red List organized by the International Union of Concerned Scientists.
"To date, most conservation efforts have also used highly invasive and destructive trammel nets to estimate their population densities and distributions underwater," lead study author Youenn Jézéquel, doctoral student at the University of Western Brittany in France, told UPI in an email.
"In this context, it is critical to find new non-invasive and non-destructive tools to study this vulnerable species in its natural environment. Passive acoustics seem very promising because it simply aims to listen ... to sounds produced by marine animals to obtain critical information," Jézéquel said.
He and his colleagues used underwater microphones, or hydrophones, to record 1,560 antennal rasps produced by 24 spiny lobsters in the Bay of Saint Anne du Portzic, France. The hydrophones were placed at different distances away from the noisy lobsters.
Using what scientists know about the dissipation of sound waves underwater, researchers were able to calculate the range of the antennal rasps based on the decibels picked up by microphones 100 meters away.
While the recordings showed smaller juvenile lobsters can produce sounds that travel just a few dozen meters, the largest spiny lobsters can generate rasps that are detectable 400 meters away.
If conditions are right and underwater background noise remains low, the loudest antennal rasps could be heard 3 kilometers, or almost 2 miles, away.
While impressive, this particular mode of sound production isn't unheard of. In fact, most people who have been outside the city have heard similar rasps in the hours after sundown.
"Interestingly, the closest animals presenting this kind of sound producing apparatus do not live underwater but live on land and are called the insects," Jézéquel said. "Spiny lobsters are notably closely related to crickets, which has bought their nicknames by fishermen as sea crickets."
According to Jézéquel, lots of followup questions remain that require further study. Scientists don't know exactly when and why spiny lobsters generate these sounds -- whether to scare predators or attract mates. Researchers are curious to find out whether individual lobsters produce distinctive acoustic signatures.
"This is only the beginning," Jézéquel said. "From now on, we need to listen more to marine ecosystems where spiny lobsters tend to live to answer most of these questions.
"For example, spiny lobsters could become new sentinel species of the environment to characterize, for example, a mechanical impact of human origin such as overfishing."