Hearing capabilities of loggerhead sea turtles (Caretta caretta) throughout ontogeny: An integrative approach involving behavioral and electrophysiological techniques

Open Access Report 2011

Final Report

While some electrophysiological auditory studies have been conducted on sea turtles, little is currently known about sea turtle hearing capabilities throughout ontogeny or how electrophysiological data correlate with behavioral responses, a necessary step for comprehensive hearing assessment. For this study we employed two independent but complementary approaches, i.e., behavioral and electrophysiological audiography, to assess hearing in two different size classes (i.e., post-hatchling and juvenile) of loggerhead sea turtles Caretta caretta. Behavioral trials involved first training turtles to respond to known frequencies, a multi-stage, time-intensive process, and then recording their behavior when they were presented with sound stimuli from an underwater speaker using a LabVIEW-based stimulus delivery and data acquisition system. A two-response, forced-choice approach was used, whereby the turtles selected one chute when sound was detected and another when it was not. Electrophysiological experiments involved submerging restrained, fully conscious turtles just below the air-water interface so that their ears were underwater but breathing was not restricted, and recording auditory evoked potentials (AEPs) using a Tucker-Davis Technologies system when sound stimuli were presented using an underwater speaker. Sound pressure levels (SPLs) and particle motions (i.e., particle velocity and particle acceleration) were also recorded. No ontogenetic differences in behavior-derived thresholds and sensitivity ranges were detected, and there was no difference in response speed (body lengths s-1) between hatchlings and juveniles or between suprathreshold and threshold trials. The only signifcant response speed difference was between correct and incorrect trials, with turtles swimming slower when making an incorrect choice relative to a correct choice. As was the case for behavior data, AEP-derived thresholds and sensitivity ranges were similar for post hatchling and juvenile sea turtles. At behavioral thresholds, particle accelerations and particle velocities were ~10-4 – 10-3 m s-2 and ~10-8 – 10-7 m s-1, respectively, which are at or below the detection limits of the most sensitive fishes. Based on these low particle motions, negative buoyancy of the turtle, and the anatomy of the sea turtle ear, which lacks an otolith-based accelerometer system, the pressure component and not particle motion component of sound mostly likely drove the observed thresholds, though this was not tested directly in this project. While the hearing frequency range detected in both behavior and AEP experiments were consistent (50 – 1200 Hz), both posthatchlings and juveniles had significantly higher AEP-derived (mean = 126.6 re 1 µPa over hearing range) than behavior-derived (mean = 97.1 re 1 µPa over hearing range) auditory thresholds. This is an important finding for it indicates that AEP tests are less sensitive than behavioral tests and should not be used to set the standard for sound exposure levels in the field. Collectively, data from this project help define the hearing frequency range and threshold of two ontogenetic stages of turtles and provide a means to evaluate future electrophysiological audiograms. However, more research in the areas of hearing loss/damage, hair cell regeneration, masking, and in situ behavioral responses to sound are needed to better define the impact of human-made sound sources on sea turtles.

Link To Publication

Similar Research

Anthropogenic sound and marine mammal health: measures of the nervous and immune systems before and after intense sound exposure

Pay-walled Journal Article 2004

Canadian Journal of Fisheries and Aquatic Sciences

Anthropogenic sound is a potential stressor for marine mammals that may affect health, as has been demonstrated in other mammals. Therefore, we have initiated investigations on...
Read More

A Brief Review of Anthropogenic Sound in the Oceans

Open Access Journal Article 2007

International Journal of Comparative Psychology

Sound in the oceans is generated by a variety of natural sources, such as breaking waves, rain, and marine animals, as well as a variety of...
Read More

Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales

Pay-walled Journal Article 2006

Animal Conservation

The human contribution to ambient noise in the ocean has increased over the past 50 years, and is dominated by low-frequency (LF) sound (frequencies <1000 Hz)...
Read More

Response and Responsibility: Regulating Noise Pollution in the Marine Environment

Pay-walled Journal Article 2007

Journal of International Wildlife Law and Policy

The ocean is becoming an increasingly noisy environment. With a rise in com-mercial shipping, resource extraction activities, and military-related activities,the underwater ocean environment is a virtual...
Read More

Influences of man-made noise and other human actions on cetacean behaviour

Pay-walled Journal Article 1995

Marine and Freshwater Behaviour and Physiology

Behavioral reactions of cetaceans to man-made noises are highly variable, ranging from attraction (e.g. bow riding by dolphins) or no response through short-term changes in behaviour...
Read More

International Regulation Of Transboundary Pollutants: The Emerging Challenge Of Ocean Noise

Open Access Journal Article 2001

Ocena and Coastal Law Journal

Transboundary pollution law poses the challenge of addressing environmental problems irrespective of boundaries in an international legal system that values, above all, territorial sovereignty of individual...
Read More

Determination of environmental sensitivity of acoustic propagation on continental shelves using an equivalent fluid parabolic equation model

Pay-walled Journal Article 1995

The Journal of the Acoustical Society of America

A coupled environment and acoustic prediction system was developed to evaluate the sensitivity of acoustic propagation on the continental shelf to water column and sediment properties....
Read More

Effects of underwater noise on auditory sensitivity of a cyprinid fish

Pay-walled Journal Article 2001

Hearing Research

The ability of a fish to interpret acoustic information in its environment is crucial for its survival. Thus, it is important to understand how underwater noise...
Read More

Effects of noise exposure on click detection and the temporal resolution ability of the goldfish auditory system

Pay-walled Journal Article 2005

Hearing Research

Hearing specialist fishes investigated so far revealed excellent temporal resolution abilities, enabling them to accurately process temporal patterns of sounds. Because noise is a growing environmental...
Read More

The effects of noise on the auditory sensitivity of the bluegill sunfish, Lepomis macrochirus

Pay-walled Journal Article 2002

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology

As concerns about the effects of underwater anthropogenic noises on the auditory function of organisms increases, it is imperative to assess if all organisms are equally...
Read More