Influence of environmental and anthropogenic acoustic cues in sea-finding of hatchling leatherback (Dermochelys coriacea) sea turtles.

Abstract

Although the visual and geomagnetic orientation cues used by sea turtle hatchlings during sea-finding have been well studied, the potential for auditory stimuli to act as an orientation cue has not been explored. We investigated the response of sea turtle hatchlings to natural and anthropogenic noises present on their nesting beaches during sea-finding. The responses of hatchling leatherback sea turtles, Dermochelys coriacea, collected from the Sandy Point National Wildlife Refuge, St. Croix, were measured in the presence of aerial acoustic sounds within hatchlings’ hearing range of 50 to 1600 Hz. The highest sound energy produced by beach waves occurs at frequencies 50–1000 Hz, which overlaps with the most sensitive hearing range of hatchling leatherbacks (50–400 Hz). Natural beach wave sounds, which have highest sound energy at frequencies of 50–1000 Hz, may be masked by human conversations (85–650 Hz) and vehicle traffic noise (60–8000 Hz). In the presence of three stimuli, a) beach wave sounds (72.0 dB re: 20 μPa), b) human conversation (72.4 dB re: 20 μPa), and c) vehicle traffic noise (71.1 dB re: 20 μPa), hatchlings exhibited no phonotaxic response (wave sounds: mean angle = 152.1°, p = 0.645; human conversation: mean angle = 67.4°, p = 0.554; traffic noise: mean angle = 125.7°, p = 0.887). These results may be due to the hatchlings being unable to localize sounds in the experimental arena. Visual and auditory cues may also converge to affect sea-finding orientation. Future studies should focus on the localization ability of sea turtles and on the role that sound may play in orientation when combined with other sensory and environmental cues.