The Role of Secondary Acoustic Cues in Sea-Finding by Green (Chelonia Mydas), Hawksbill (Eretmochelys Imbricata), and Leatherback (Dermochelys Coriacea) Sea Turtles

While light and slope cues have been shown to impact sea-finding in hatchling sea turtles, the possible effects that naturally occurring acoustic cues have not been well explored. We monitored the behavior of hatchling leatherback (Dermochelys coriacea), green (Chelonia mydas), and hawksbill (Eretmochelys imbricata) sea turtles, collected from nesting beaches within the St. Croix Sandy Point National Wildlife Refuge in the presence of recorded beach surf sounds (72.0 dB re: 20 μPa) and simulated moonlight (4000K, >1 lumens). We examined hatchling response to trial auditory signals in a circular arena raised 14.0 cm off the floor. The arena’s circular platform was surrounded by 36 converging cushioned pitfall bins constructed to correspond to 10 degree intervals. Each bin had a degree range of 10 degrees and the midpoint of this range was used for statistical analysis. For example, if a hatchling crawled into bin 1 they were deemed to be orienting between 0-10 degrees and 5 degrees was the value used for analysis. We encased the entire arena in a light-proof tent to eliminate external light cues. A speaker producing the recorded beach wave sounds was placed outside the tent and moved to alternating locations (in relation to compass bearings: North, South, East, and West) to ensure turtles were orienting toward the speaker and not in relation to any given compass bearing. Simulated moonlight was presented alone and at both the same (0°), opposite (180°), or 90° locations to the speaker. We suspended the speaker producing the trial sounds from a PVC frame above the table and off the floor to prevent vibrations. We leveled the platform to eliminate potential slope cues. Nest ID/Location indicates the nest identification number from the Sandy Point National Wildlife Refuge, St. Croix. Bin indicates the bin the hatchling oriented into relative to the speaker location. Bin corrected indicates the bin number when all 4 speaker locations were standardized after location was determined not to have an effect. A failed trial indicates one in which the hatchling did not enter a bin within the 5 minute trial time.