New Discoveries about Turtles

Recent studies indicate that green turtle hatchlings ‘swim’ their way to the surface rather than ‘dig’ during the time between hatching and coming out of the sand. These findings could significantly impact global conservation efforts for declining turtle populations.

In a paper published today in Proceedings B, researchers from the University of New South Wales’ School of Biological, Earth and Environmental Sciences utilized a small device known as an accelerometer to unveil new data about the behaviors of hatchlings as they exit their nests.

Sea turtle eggs are typically buried 30 to 80 cm deep. After hatching, turtle hatchlings make the journey to the sand’s surface over a span of three to seven days. However, since this process takes place underground, our understanding of those initial days in a hatchling’s life is quite limited.

The innovative research revealed that hatchlings maintained a head-up orientation while buried and, surprisingly, moved vertically through the sand by rocking back and forth instead of the expected side-to-side motion associated with digging.

“When I think about a newly hatched turtle, it’s completely surrounded by darkness and has no indication of which way leads to the surface, yet it manages to orient itself and move upwards regardless,” explains Mr. Davey Dor, the study’s lead author and PhD candidate. “Our initial observations and validation of this new method open up many new questions in sea turtle ecology.”

Exploring Underground Life

We often picture hatchlings eagerly making their way across the sand to reach the ocean. But what precedes that moment?

After breaking free from their eggs, hatchlings start moving through the sand until they finally break the surface.

“It was around 64 years ago that researchers first observed the transition from egg hatching to surfacing,” Mr. Dor remarks. “Since then, various methods have been attempted to study this phase, including using glass viewing panes and microphones to monitor their movements.”

Each of these prior techniques had its own limitations, making it challenging to investigate the early days of turtle hatchlings. “People often overlook the effort required for these tiny turtles to navigate through sand in complete darkness and with little oxygen,” adds Associate Professor Lisa Schwanz. “This process occurs right beneath our feet, yet we have lacked the technology to adequately understand it.”

Thus, Mr. Dor, A/Prof. Schwanz, and Dr. David Booth from the University of Queensland sought to discover new methods to observe and study this obscure process.

Innovative Accelerometer Backpacks

Accelerometers, which track shifts in speed or direction, have previously been applied in studying animal movements, behaviors, and physiological responses.

“The accelerometer we used operates on a simple principle: it measures acceleration from three different axes, capturing changes in velocity during forward-backwards movement, up-down motion, and side-to-side movement,” explains Mr. Dor. “However, this application of an accelerometer was unprecedented.”

The fieldwork was conducted on Heron Island, a long-studied nesting site for green turtles located in the southern Great Barrier Reef, where nesting typically occurs from December to March.

“Once we identified the nests, we patiently waited for about 60 days for the eggs to mature,” Mr. Dor recounts. “Three days before hatching, we placed a hatch detector next to ten different nests. This unique device tracks voltage at the nest location to signal when the hatchlings break out of their eggs.”

Upon receiving confirmation that the hatching had occurred, the researchers carefully excavated the nest, selected the hatchling nearest to the surface, and attached a lightweight accelerometer before replacing the sand around it. “We carefully put the sand back just like we found it,” Mr. Dor says.

Then came the waiting period to see when the hatchlings would emerge. “We checked the nest every three hours, and when they finally made their appearance, we retrieved the accelerometer from the hatchling,” he explains.

This accelerometer offered new insights into the direction, speed, and duration it took for the ten hatchlings to reach the surface. “The analysis revealed that hatchlings consistently maintained a head-up position even in complete darkness surrounded by sand,” notes Mr. Dor. “We observed that their movement and resting intervals were relatively brief, resembling swimming rather than digging. Moreover, they tended to limit their movement to nighttime as they neared the surface,” he adds.

Conservation Efforts and Nest Management

Sea turtle populations are declining in many regions worldwide, with several species classified as endangered. The nesting phase presents a critical vulnerability for these populations, prompting conservation efforts that often involve nest management, such as relocation, shading, and hydration.

Nest relocation has been common for many years and is expected to continue as climate change and rising sea levels exert pressure on turtle nesting. Nonetheless, changing factors like moisture and temperature conditions after a nest is moved can impact crucial traits related to hatchlings’ performance, including speed and movement capabilities.

“Modifying nest characteristics, such as moisture content and depth, could have unknown impacts on hatchlings,” Mr. Dor highlights. “Thus, understanding hatchling behavior within the sand column is essential for future conservation strategies.”

While it’s known that hatchlings face numerous predators during their dash across the sand towards the ocean, “it’s also the case that some hatchlings never reach that point,” A/Prof. Schwanz indicates. “We know so little about what determines the success of one hatchling over another at this stage, making it crucial to identify the factors that could influence this outcome.”

Paving the Way for Future Research

The findings from this study demonstrate that utilizing accelerometers to track hatchlings yields numerous advantages, including tracking movements and behaviors, along with the capability to study turtles during phases when visibility is limited.

These insights have also shifted prior perspectives on the early experiences of hatchlings in the sand.

“There are numerous aspects that remain unclear due to our inability to observe this phase of their lives, but we aim to change that with this new method, particularly regarding optimal conservation practices,” Mr. Dor comments.

The following summer, Mr. Dor returned to Heron Island to equip multiple hatchlings from a single nest with accelerometers. “By analyzing this next batch of data, we hope to assess how synchronized their movements are, as there’s a theory regarding potential coordination among turtles or whether there’s a division of labor,” A/Prof. Schwanz concludes.