Sea turtles are found in waters all over the world, offshore as well as inshore. As a result they are likely to be exposed to a variety of man-made sounds. Although all species of sea turtles are threatened or endangered, there is little known about the hearing capabilities of sea turtles or how they are impacted by sound. Until now, the information available was based solely on physiological tests. However, there is a behavioral study in progress at the New England Aquarium with a Green Sea Turtle (Chelonia mydas) named Myrtle. The hearing capabilities of this turtle are being investigated using psychophysical methods, standard operant conditioning techniques, and positive reinforcement schedules commonly used with marine mammals. This effort is funded by the Office of Naval Research and is conducted in collaboration with the University of Maryland, College Park, Maryland.

Myrtle is approximately 60 years old. She is housed in the New England Aquarium's landmark coral reef exhibit along with 700 fish and two other turtles. Despite the challenges related to working with a turtle and the distractions inherent to working with an individual animal in an exhibit environment, a training protocol and an experimental design have been developed making it possible to test Myrtle's hearing capabilities.

Since Myrtle was responsive to standard training techniques, she learned the basic behaviors required to test a variety of experimental designs and apparatus. Ultimately a Go/No-Go paradigm proved to be the one that Myrtle responded to most consistently and with a minimum of difficulty. She was not required to maintain a specific station position throughout a session. It was clearly difficult for her to do so. Instead, she had to initiate a trial by swimming to and touching a light box. This triggered a light, and sometimes a sound, to go on - indicating the start of a trial. Myrtle learned to touch the light again in the absence of a tone and to indicate that a tone was detected by swimming to and touching an under water response paddle. She was rewarded with fish, shrimp, crabs, vegetarian gel cubes, or lettuce for each correct response. A shield was dropped in front of the light after each trial to indicate the end of a trial.

Incorrect responses were not rewarded. The shield was simply raised again encouraging her to initiate a new trial. The preliminary data indicates that Myrtle hears tones ranging from 100Hz to 500Hz. Studies indicate that at 200hz her threshold is between 107dB and 119dB, and at 400Hz threshold is between 121dB and 131dB. These results are invaluable in that they represent the first and only behavioral data available on the range of sea turtle hearing capabilities. However the data should be interpreted cautiously because of Myrtle's age. It is reasonable to predict that younger turtles probably have a slightly wider bandwidth and are able to hear lower intensity sounds than Myrtle. Plans for the future include completing Myrtle's audiogram, studying masking thresholds, critical bands, critical ratios, and directional hearing capabilities.