An overabundance of underwater noise may cause temporary hearing loss in turtles, according to new study. This behavior, which has been seen in other marine species such as dolphins and fish, was not well understood in reptiles until recently, and it highlights another possible threat to aquatic turtles. Passing ships and offshore development may contribute to this excessive volume of sound, which is referred to as underwater noise pollution.
These early results are part of a research conducted by the Woods Hole Oceanographic Institution and presented at the 2022 Ocean Sciences Meeting, which will be held online from February 24 to March 4, 2022.
“This is the first research to show that these animals are susceptible to underwater hearing loss after being exposed to loud noise,” said Andria Salas, a WHOI postdoctoral scientist and study co-author. “We’ve hypothesized that turtles, like other animals, incur hearing loss when exposed to sufficiently loud noises, but there hasn’t been any evidence gathered particularly on turtles.”
Some species have been demonstrated to employ underwater auditory communication, and aquatic turtles are projected to depend on their sense of underwater hearing for environmental awareness, such as navigation or detection of dangerous predators. Previous research has looked at the consequences of excessive noise on a variety of creatures, including squids, fish, and whales, in both fresh and saltwater habitats. Salas claims that little research has been done on reptiles such as turtles.
The findings of this research are the first to show that underwater noise causes hearing loss in turtles, indicating that turtles are more sensitive to sound than previously thought.
Salas and her colleagues, notably WHOI associate scientist Aran Mooney, were shocked by how a very modest amount of noise affected the turtles’ hearing. Noise exposure causes a transient threshold shift (TTS), which is a reduction in the animal’s hearing sensitivity as a consequence of the noise. There is a data gap for endangered sea turtles and aquatic turtles in general due to the lack of TTS investigations in turtle species.
“If this happens in nature, turtles will have a harder trouble detecting noises in their surroundings on these timeframes, including sounds required for communication or to warn them of oncoming predators,” Salas added. “More than half of all turtle and tortoise species are endangered, and noise pollution is another factor to consider as we seek to safeguard these creatures.”
“It was startling to see that noise may cause underwater hearing loss in turtles, and then it was shocking to discover that this hearing loss occurred at considerably lower levels than expected,” Mooney said. “Moreover, despite the noise being strong enough to cause temporary hearing loss, the turtles remained quite quiet (or showed no behavioral reaction).
Notably, in animals, transient hearing loss is a natural physiological occurrence. We’re suddenly seeing it all over the place (mammals, birds, fish, and reptiles). However, in this scenario, it may be a predictor of more serious, more harmful noise effects, such as irreversible hearing loss or auditory impairment.”
The researchers tested two non-threatened freshwater turtle species in order to complete the study. They detected minuscule neuronal voltages made by the turtles’ auditory systems as they heard noises using a minimally invasive device put just under the skin above their ear. Hearing is tested quickly, in only a few minutes, and is comparable to how hearing is measured noninvasively in human neonates. They first identified the lower threshold of turtles’ underwater hearing and the tones (frequencies) they heard best before exposing them to intense white noise (akin to the sound of radio static).
The researchers measured turtle hearing for roughly an hour after exposing them to noise and then removed them from the noise to see how they recovered their short-term underwater hearing, and then tested two days later to see whether recovery was complete. While the turtles’ hearing was always restored, hearing loss might last anywhere from 20 minutes to over an hour. However, some people’s hearing did not completely recover by the end of the testing hour, suggesting that they required longer time to recover from the noise. For many days, one turtle’s hearing was impaired.