For the world’s smallest sea turtles, life in the ocean is getting pretty noisy. These relatively little turtles (on average they’re still 75 to 100 pounds) mostly found in the Gulf of Mexico already face fishing gear accidents, seacraft collisions, plastic pollution, and habitat deterioration, and now excess noise may be harming the critically endangered and rare Kemp’s ridley sea turtles (Lepidochelys kempii).
We say might because even though these sea turtles share waters with extremely busy shipping lanes, scientists know very little about their underwater hearing. As such, a team of researchers set out to understand what, exactly, these animals can perceive in terms of sound.
“Understanding hearing ability is a fundamental step in determining whether human-generated noise could affect a species,” Charles Muirhead, the co-author of the recent study published in The Journal of the Acoustical Society of America and a researcher at Woods Hole Oceanographic Institution’s Sensory Ecology and Bioacoustics Lab, tells Popular Science. “Our goal was to provide a more robust and representative understanding of their hearing sensitivity so that future research and conservation efforts can be built on stronger scientific foundations.”
This notion is particularly significant given the fact that Kemp’s ridleys are the world’s most critically endangered sea turtles.
Muirhead and his colleagues put sensors on Kemp’s ridley sea turtles’ heads and recorded the electrical signals that passed through their auditory nerves as they played sounds from 50 to 1,600 hertz. In the spectrum of human hearing, 50 hertz is on the lower side.
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This approach revealed that the turtles’ greatest hearing was at about 300 hertz, and that they began to struggle with higher frequencies. It appears that Kemp’s ridleys’ best hearing aligns with the low-frequency band that hosts a significant amount of sounds, presumably from industrial operations in the ocean like oil and gas drilling and vessel traffic, according to Muirhead.
“This is significant because we’ve known that their movements and distribution overlap with industrial and boat noise sources both in space and time—and we’ve now confirmed that the turtles are capable of detecting these sounds,” Muirhead says. “However, detecting sound does not automatically mean it causes harm or disturbance. Whether noise ‘bothers’ turtles depends on several factors, including sound level, duration, distance from the source, and the behavioral or ecological context in which the exposure occurs.”
Now that we know what these turtles can hear, future research can investigate just how human sounds impact them and what that means for conservation efforts.
More broadly, Muirhead explains that, “understanding how animals perceive their environment is essential for effective conservation.Hearing is only one piece of the puzzle.”
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