Scientists at the University of New South Wales (UNSW) are using lightweight 'backpacks', also known as accelerometers, to try and find out more about the way sea turtles get to the surface of the sand after hatching from their underground nests.
The study, conducted on Heron Island in the Great Barrier Reef, Australia, reveals critical information that could help shape turtle conservation efforts, say the researchers, who findings were published in Proceedings B.
Sea turtles, which are endangered in many parts of the world, bury their eggs in nests 30–80cm deep. Once hatched, the newborn turtles make their way to the surface of the sand over three to seven days. But because this all happens underground, we have very little understanding of the first few days of a hatchling’s life, says Davey Dor, who led the study as part of his PhD.
“When I visualise a hatchling that has just come out of its egg, it is completely in the dark in its surroundings. There’s no sign to point which way is up toward the surface – yet they will orientate themselves and move upwards regardless."
For decades, researchers have struggled to study turtle hatchlings as they make their way to the surface after hatching. Earlier methods, such as glass viewing panes and microphones, have provided limited insight into their underground journey.
“It happens right under everyone’s feet, but we haven’t had the technology to really understand what is happening during this time,” says Associate Professor Lisa Schwanz, a co-author of the study.
The use of accelerometers – a device previously used to study animal movement – has now offered a clearer picture of how these tiny creatures move, explains Dor.
"The simple principle of the type of accelerometer we used is that it measures acceleration from three different angles. So it can measure a change in velocity in a forwards and backwards motion, an up and down motion and a side to side motion.”
The study took place on Heron Island, a long-term monitoring nesting site for green turtles in the southern Great Barrier Reef.
"After locating the nests, we waited for approximately 60 days for the eggs to develop,” says Dor.
“Three days before they hatched, we put a device called a hatch detector next to 10 different nests. This unique instrument measures voltage at the nest site and lets us know when the hatchlings had hatched out of their eggs.”
As soon as the team became aware that the eggs had hatched, they carefully located the hatchling closest to the surface and attached them with an accelerometer, before placing it back. “We then gently layered the sand back in the way it was found,” explains Dor.
“We checked the nest site every three hours and when they did finally emerge, we retrieved the accelerometer from the hatchling carrying it.”
The accelerometer provided new data on the direction, speed and time it took for the hatchlings to emerge, says Dor. “We analysed the data and found that hatchlings show amazingly consistent head-up orientation – despite being in the complete dark, surrounded by sand.
"We found that their movement and resting periods are generally quite short, that they move as if they were swimming rather than digging, and that as they approach the surface of the sand, they restrict their movement to nighttime."
What do the findings mean?
The researchers say that the work confirms that using accelerometers to monitor hatchlings provides many benefits, including data of movement and behaviours. But perhaps most crucially, the technique means turtles can be studied largely without disturbance when visibility of them is limited.
These findings have also provided new insights and changed previous assumptions about hatchlings' earliest days in the sand.
“There are lots of factors that we don't really understand because we haven't been able to observe this stage of their lives, but we hope this will change as a result of this new method, particularly in answering questions about best conservation practices,” says Dor.
Find out more about the study Swimming through sand: using accelerometers to observe the cryptic, pre-emergence life-stage of sea turtle hatchlings.
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