Sea turtles suffer from hearing loss caused by noise pollution

Coastal and pelagic soundscapes are becoming more and more noisy, as offshore energy development, shipping and construction activities become more widespread and intense. One acoustic impact of the louder noise is a reduction in hearing sensitivity recorded in some marine and freshwater animals, including fish, squid and whales.

Researchers now say that reptiles, such as turtles, are also likely to experience hearing loss as a result of exposure to underwater noise pollution. The results of their recent study will be presented at the 2022 Ocean Sciences Meeting, being held online until the 4^th of March. 

“Our preliminary findings are the first to support that these animals are vulnerable to underwater hearing loss after exposure to intense noise,” said Andria Salas, who is a researcher at Woods Hole Oceanographic Institution and will present the findings of the research. “We have assumed that turtles experience hearing loss when exposed to sufficiently intense sounds as observed in other animals, but there hasn’t been any data collected specifically on turtles.”

The researchers used two non-threatened species of freshwater turtles in their experiments to determine the impact of loud noise on hearing. They inserted a minimally invasive electrode just under the skin above a turtle’s ear, to monitor the very small electrical voltages created by the turtle’s auditory system when it hears sounds. Before exposing the turtles to loud noise, the researchers first determined the lower threshold of turtles’ underwater hearing and which sound frequencies they heard best.

They then exposed the turtles to loud noise before removing them from the source and continuing to measure hearing sensitivity over the next hour to determine the extent of underwater hearing loss and whether this recovered in the short term. The turtles’ hearing was checked again two days later, to establish whether it had recovered fully. 

The researchers found that, while the turtles always recovered their hearing, sensitivity loss could last anywhere from 20 minutes to over an hour. In some instances, however, hearing had not recovered by the end of the testing hour, indicating that the turtles needed more time to recover fully from the noise exposure. The hearing of one turtle was affected for multiple days.

Salas and her colleagues were surprised by the relatively low level of noise that caused these changes to the turtles’ hearing, which is essential for communication and avoiding predators. The new findings could have implications for the survival of some threatened turtle species. 

“If this occurs in nature, turtles would be less able to detect sounds in their environment on these timescales, including sounds used for communication or warning them of approaching predators,” she said. “Over half of turtle and tortoise species are threatened, and noise pollution is an additional stressor to consider as we work towards protecting these animals.”

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By Alison Bosman, Earth.com Staff Writer