Turtle hatchlings with tiny backpacks reveal what goes on under the sand

Baby green sea turtles are the latest in a long list of animals given their very own backpacks to help scientists study their behaviour.

Hatchlings are tiny and vulnerable and make a mad dash to the sea to avoid predators. But Australian researchers wanted to understand more about how they make their way to the surface of the sand after emerging from their eggs, which are buried in nests 30 to 80cm deep.

The findings have important implications for sea turtle conservation management, which often focuses on interventions such as relocating, shading, and watering nests.

Until now, scientists have lacked the technology to be able to observe this critical phase of the turtles’ lives.

“We analysed the data and found that hatchlings show amazingly consistent head-up orientation – despite being in the complete dark, surrounded by sand,” says David Dor, who led the research as part of his PhD at the University of New South Wales, Australia.

“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.

“There’s no sign to point which way is up toward the surface – yet they will orientate themselves and move upwards regardless.”

The research took place on Heron Island off the coast of Queensland – a long-term monitoring nesting site for green turtles in the southern Great Barrier Reef.

The team located 10 nests and monitored them to determine exactly when the baby turtles hatched. They carefully dug down, selected the hatchling closest to the surface, attached a lightweight, miniature accelerometer onto its back, and placed it back before gently layering the sand back.

“We checked the nest site every 3 hours and when they did finally emerge, we retrieved the accelerometer from the hatchling carrying it,” says 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.”

Current conservation strategies which alter nest characteristics, such as sand moisture and depth, could have consequences for hatchlings that aren’t yet understood.

“This means knowledge of hatchling behaviour in the sand column – and its links to offspring success – is key to future conservation practices,” says Dor.

The paper appears in Proceedings of the Royal Society B.