Raine Island - Nature's Cradle on the Edge of the Coral Sea
Satellite Web Cast From Turtle Heaven and Hell
Turtle Tagging Research Project Background
Over the last 50 years or so biologists around the world have been studying what turtles do when they come ashore to lay a clutch of eggs. However there's been very little research into what turtles do during the two week period between laying successive clutches of eggs when at a nesting beach. This understanding has remained elusive because of the difficulties involved in tracking turtles when they are at sea. Modern technology now provides us with some of the tools to be able to piece together a few pieces of the puzzle. Raine Island makes an interesting study site because the reef edge surrounding the coral cay plunges precipitously- travel only 50 meters offshore and the sea floor is several hundred meters down, a bit further and the bottom drops right away to over 1200 metres!. This tracking project opens a small window of understanding into such things as how long turtles can hold their breath when diving, how long they spend at the surface between dives and deep they are able to dive. The preliminary data are very exciting and show that among other things, turtles vary their diving behavior depending on whether they are diving during the day or at night.

In order to understand where turtles are going when they are at sea, we attach an instrument called a "Time, Depth and Temperature Recorder" or "TDR", for short. This cylinder shaped instrument is about an inch long and a quarter of an inch wide...about the same size as a ball point pen cap. The TDR has a in-built thermometer and pressure gauge and takes time, depth and temperature recordings every ten seconds over a two week period and stores the information in it's memory. When the turtle comes back to the beach to lay another clutch of eggs, we take the TDR off her and download the data to a computer.
When the information is put into a graph, such as the one below, we can see what depths the turtle was swimming to and that the turtle does quite different dive types during the day time compared to night time. During the day time she does a lot more dives to a shallower depth than at night time. It may be that during the night, when she's not able to see lurking predators very well, that she just wants to get to the surface for a breath of air, then get straight back to her resting place within the reef as quickly as possible. During the day she can surface to breath more often because she can see whats around and therefore avoid anything that may want to eat her.
This may be actually what happened where, as you can see on the graph, she made several dives to as deep as 50 metres.
What would have made a turtle want to dive this deep? It may well be that a hungry shark paid a little too much attention to her and she decided to get out of there by swimming to that depth. It is hoped that one day the technology will be available to help us unravel the secrets behind this type of behavior.

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