For a long time, many people believed sea turtles were silent, graceful creatures of the ocean depths. This perception stemmed from the challenges of observing their hidden lives and the subtle nature of their underwater interactions. However, scientific research is now revealing a surprisingly active acoustic world beneath the waves, challenging the assumption of their muteness. Scientists are discovering these ancient mariners engage in a variety of vocalizations, suggesting a more complex auditory landscape.
The Unexpected Symphony
Sea turtles make sounds, a discovery that has reshaped our understanding of their behavior. Their vocalizations are low-frequency and brief, making them difficult for humans to detect without specialized equipment. The historical lack of awareness was largely due to these subtle characteristics and the inherent difficulties of studying sounds in the vast ocean.
Recent studies confirm that sea turtles possess broad and complex acoustic repertoires. Researchers have recorded various sounds from different species and life stages, including embryos, hatchlings, juveniles, and adults. Sea turtles are most sensitive to low-frequency sounds, below 1,000 Hz, with optimal hearing ranging from 200 to 750 Hz depending on the species and age.
A Closer Listen
Sea turtles produce a variety of sounds, including clicks, grunts, chirps, and moans. For instance, the flatback turtle (Natator depressus) makes sounds resembling croaks, scrapes, and chirps. Juvenile green sea turtles (Chelonia mydas) produce at least ten different sound types, categorized into pulses, low-amplitude calls, frequency-modulated sounds, and squeaks. These vocalizations are not produced through vocal cords, as sea turtles lack these structures.
Instead, sea turtles generate sounds through alternative mechanisms. A primary method involves the controlled expulsion of air from their lungs, which can create grunting or hissing sounds. Movements of their shells or jaw movements may also contribute to sound production through vibrations. Additionally, some sounds, such as those made by nesting leatherback turtles, can be a result of breathing, throat movements, and grunting during egg-laying.
The Language of the Deep
Scientists hypothesize that sea turtle vocalizations serve various purposes, ranging from communication during early life stages to interactions in adulthood. For example, within their eggs, sea turtle embryos and hatchlings make sounds like chirps, grunts, and complex hybrid tones to coordinate synchronized hatching. This coordinated emergence, often called a “nest boil,” helps numerous hatchlings surface together, potentially overwhelming predators and increasing their chances of survival.
Beyond the nest, these sounds are believed to facilitate communication for social interactions, including mating rituals. Some studies suggest sounds may be used for signaling distress, coordinating group movements, or assisting in navigation. While research on adult sea turtle communication remains less documented compared to hatchlings, emerging evidence suggests these acoustic signals are significant for their social and survival behaviors. Recent findings indicate that green turtles respond to vocalizations associated with alerts, suggesting a potential for acoustic deterrence in conservation efforts.
Unveiling Underwater Voices
Studying sea turtle sounds presents challenges due to the vastness of their marine habitats and the subtle nature of their vocalizations. Researchers employ specialized underwater microphones, known as hydrophones, to record these sounds. Advanced acoustic analysis techniques are used to interpret the collected data, helping scientists categorize and understand the different types of sounds produced. Analyzing frequency characteristics and patterns differentiates sea turtle sounds from background noise.
The subtlety of these sounds and the expansive ocean environment necessitate long-term monitoring and innovative approaches. Despite difficulties, this research is important for understanding sea turtle behavior, particularly how they perceive and respond to their acoustic environment. Insights gained from studying their vocalizations can inform conservation efforts, such as developing acoustic deterrents to reduce bycatch in fishing gear or assessing the impact of human-generated noise on their populations.