Effect of noise on sand digging and emergence activities in green turtle (Chelonia mydas) hatchlings

Abstract

Anthropogenic noise affects animal behavior and physiology. However, relatively few studies have been conducted on the effects of noise on beach-associated animals. This study evaluated the effects of noise on sound emission, sand digging activity, and emergence from the sand surface by green turtle (Chelonia mydas) hatchlings. Acoustic recorders and infrared cameras were used to investigate the behavior of hatchlings in sand-filled chambers under three acoustic conditions: 1) a control treatment, which was silent throughout the experiment; 2) an environmental noise treatment, which exposed the hatchlings to white noise (WN) at a sound pressure level (SPL) approximately 13 dB higher than that of the control, which is similar to that of a natural beach; and 3) a loud noise treatment, which exposed them to WN at an SPL approximately 25 dB higher than that of the control. The WN ranged from 0 to 4 kHz with a repeating cycle of 30 min sound emission and 2 h 30 min silence. Sound emissions from green turtle hatchlings were detected; however, the amount of sound emissions was too small to discuss their ecological significance. The time to emergence and total number of digging bouts in the 24 h pre-emergence periods were not significantly different among treatments; however, the number of digging bouts was significantly higher during loud noise exposure. The response to loud noises may play a role in allowing hatchlings to escape from threats and/or coordinate synchronous behavior among multiple individuals. However, because the number of digging bouts decreased after loud noise exposure, prolonged exposure to loud noise may have detrimental effects on hatchlings, such as depletion of the energy reserves available to the hatchlings. Thus, anthropogenic noise on or around beaches and it effect on animals should be carefully considered.