Tracking sea turtle hatchlings - A pilot study using acoustic telemetry

Abstract

Understanding the movements of turtle hatchings is essential for improved understanding of dispersal behaviour and ultimately survivorship, life history strategies and population connectivity. Yet investigation of in-water movement has been hampered by the small size of hatchlings relative to the size of available tracking technologies. This has resulted in the use of labour intensive visual tracking methods, or active tracking methods with high transmitter to body weight ratios. These methods are confounded by the presence of the observer, the size of the tag, usual small treatment sample sizes and studies that are constrained to daylight hours when turtles hatch predominantly at night. Passive acoustic monitoring using new miniature tags can overcome these limitations.We tested the effectiveness of active and passive acoustic tracking in monitoring turtle hatchling movement in order to measure the influence of artificial light on newly hatched turtles once they enter the water. A Vemco VR2W Positioning System (VPS) comprising an array of 18 VR2W receivers was deployed in the surf zone to detect signals from acoustic-coded transmitters (1.14 ± 0.06% of body mass) attached to 26 flatback turtle hatchlings released into the array. A total of 1328 detections were recorded for 22 hatchlings with turtles spending a mean of 16.63 ± 5.89. min in the array. The test detection range for this technology in the surf-zone was 50-100. m and was influenced by wave noise and shallow deployment. Cyclonic conditions hampered the experiment and resulted in an inconclusive test of light effects. Three additional instrumented flatback hatchlings were followed in a small boat using a mobile acoustic receiver and directional hydrophone up to 2. km from shore. Passive acoustic monitoring is a viable technology for tracking small marine animals and removes many of the confounding effects of other telemetry methods. It has great potential to examine natural and anthropogenic factors influencing orientation and behaviour during a crucial stage in turtle life history - their initial movement from the beach through predator-rich, near shore waters. While the data obtained by passive acoustic monitoring is limited in its spatio-temporal coverage, being constrained by the size of the array, active acoustic tracking can be applied over larger scales. Such studies will be particularly important for assessing the impacts of anthropogenic pressures that have changed the natural light, noise or wave environments and for providing behavioural data to improve and validate bio-physical models of the migration and dispersal of young turtles. © 2012 Elsevier B.V.