Tracking leatherback (Dermochelys coriacea) hatchlings at sea using radio and acoustic tag

Abstract

For leatherback turtles relatively little is known about the “lost year(s)” – the time elapsed between a hatchling’s first contact with the ocean and the moment it is sighted again as a juvenile in neritic foraging grounds (Carr 1987) – and the factors that might drive the oceanic dispersal during this phase. Although floating particle models have been used to predict dispersal pathways of sea turtle hatchlings (Blumenthal et al. 2009), on the near-shore scale, where remotely sensed current data are unavailable, the trajectories taken by hatchlings are more difficult to predict. Frenzied swimming and strong coastal currents may distort the predictions of these “passive drifter” models. This justifies the need to study the actual movements of neonates as well as the near-shore processes that influence them. Tracking hatchlings can be challenging. Due to the animals’ small size, the technological options are limited: satellite based transmitters are (still) too large and heavy so tracking efforts need to be carried out entirely in-situ with lighter tags. Neonate sea turtles have been tracked successfully with miniaturized radio transmitters that were either fitted directly onto the hatchlings’ carapace (leatherbacks: Liew & Chan 1995) or tethered to a float or “bobber” (green turtles: Okuyama et al. 2009)