Green turtle with transmitter, Heron Island

The PTT (ST-3 Model) was constructed by Telonics Inc. USA and contained software developed by researchers in the United States, which recorded water temperature, dive times and dive counts. The PTT, powered by two lithium D-cell batteries, was housed inside a waterproof PVC tube eight centimetres in diameter and thirty-four centimetres long. The housing was pressure resistant to 150 metres depth.

The PTT was attached to the turtle with a 0.5 metre flexible stainless steel cable linked to stainless steel attachment plates which were bolted to the rear edge of the turtle carapace. Ferrous bolts were used as these would corrode in approximately 12 months, releasing the PTT and the attachment plates from the turtle about the same time as the batteries failed.

A saltwater switch built into the housing was designed to activate the PTT whenever the turtle was at the water's surface. While switched on, the PTT transmits signals at regular intervals. Orbiting National Oceanic and Atmospheric Administration (NOAA) satellites receive transmissions from PTTs in visibility during passes and are equipped with the Argos Data Collection and Location System¹ which calculates the location of the turtle for each transmission received. In this way the turtle can be tracked on its migration.

There were several concerns for the turtle as a result of this research. There was the possibility of the tether becoming entangled and trapping the turtle, as well as the possibility of infection or damage from bolt holes drilled through the edge of the carapace. While procedures were designed to minimise any discomfort or the likelihood of infection for the turtle as a result of this research, it was not known whether the turtle would become entangled. This was a risk that was weighed against the information about the turtle migration which might be gained by the research. The project was thoroughly scrutinised and passed by the then Australian Nature Conservation Authority Animal Ethics Committee.

The satellite telemetry data showed that after leaving Heron Island the turtle travelled 300 kilometres north to Broad Sound. From there she travelled 1800 kilometres north to Torres Strait and then a further 1200 kilometres west into northern Australian/southern Indonesian waters. The turtle was tracked for 234 days and migrated over 3300 kilometres from her nesting site (figure 1).

Figure 1. Post-nesting migration of green turtle from Heron Island into the Arafura Sea, a distance of over 3300 kilometres.

Despite the success of the research in terms of its results, I often wondered about the fate of this turtle - had I caused its death as a result of this research? I recently received a letter from Dr Colin Limpus, head of the Queensland Turtle Research Project, Queensland Parks and Wildlife Service, informing me that the turtle had returned to Heron Island for the 1997-98 nesting season after an eight-year absence or remigration interval. The turtle was detected by the Queensland Parks and Wildlife Service turtle research team during their beach census study and they observed that there was no obvious injury from the PTT attachment and no attachment metal remained on the turtle.

The news that the turtle was alive and well was great news to me. She remained at Heron Island for the full nesting season, nesting six times before setting off on her migration north. And this time we have a good idea of where she is going.

Reference Spring, C.S. 1994, Satellite Tracking Green Turtles in Australian Waters - Preliminary Results, in Proceedings of the Australian Marine Turtle Conservation Workshop held at Sea World Nara Resort, Gold Coast, 14-17 November 1990: Queensland Department of Environment and Heritage and the Australian Nature Conservation Agency, pp.192-197. 1 The Argos system is a cooperative project of the Centre National d'Etrudes Spatiales (CNES) of France, the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration (NASA). The primary purpose of Argos is to collect environmental data.