Functional measures of sea turtle hearing

In this study, sea turtle hearing is investigated from two perspectives: morphometrically by analyzing variations in auditory anatomy among stages and species and physiologically by brainstem evoked potential techniques. Sea turtles employed in this work were provided byNMFS Sea Turtle Stranding and Salvage Network. Auditory brainstem responses (ABRs) were collected from multiple species and life stages of live sea turtles using an stimulus coupled directly to the turtle's tympanum underwater. A three electrode array was used to record the evoked responses to stimuli. Anatomical data were obtained by computerized tomography (CT and MRI) and by conventional histology. ABRs were obtained from 12 hatchling through sub-adult turtles (Lepidochelys kempi), (Chelonia mydas), (Caretta caretta). The data show that juvenile green turtles have a slightly broader hearing range (100-800 Hz; best sensitivity 600-700 Hz ) than sub-adults (range 100-500 Hz). Kemp's Ridleys had a more restricted range (100-500 Hz) with most sensitive hearing at 100-200 Hz. Although this project suggests there are measurable age and species variations in response to underwater sound, the overall results are consistent with prior results for aerial and vibrational stimuli (C. mydas, 200-700Hz, Ridgway et aI, 1969); (C. caretta, 250-1000 Hz, Bartol et aI, 1999).