Auditory Evoked Potentials of the Loggerhead Sea Turtle (Caretta caretta)

Abstract

Much of the published research on the auditory ability of sea turtles centers on anatomy, and from these anatomical studies, we hypothesize that the loggerhead sea turtle's (Caretta caretta) hearing range centers around low-frequency sounds. To validate this hypothesis, we examined thresholds of juvenile loggerheads by collecting auditory evoked potentials derived from two types of vibrational stimuli: low-frequency clicks and tone bursts. The broadband click elicited clear auditory brainstem responses (ABRs) that could be tracked to threshold; a mean click threshold for 35 juvenile loggerheads was -10.8 dB re: Ig rms ? 2.3 dB SD. ABR recordings from the low frequency tone bursts were similar in form to the click data and indicated the range of effective hearing to be from at least 250 Hz to 750 Hz. The most sensitive threshold was recorded at the lowest frequency tested, 250 Hz, with a mean threshold of -26.3 dB re: Ig rms ? 2.3 dB SD. Historically, ABRs have been used as a technique to evaluate audition and acoustic threshold, and we feel confident that the procedures developed here are both valid and effective when used on sea turtles.