In the pristine island chain of Vava‘u, in the Kingdom of Tonga, the beaches are more than just beautiful - they are critical nesting grounds for some of the ocean’s most ancient and endangered species: sea turtles. But beneath the surface of this idyllic setting, the sands are heating up, and with them, the future of turtle populations is becoming increasingly uncertain.

Led by the Vava'u Environmental Protection Association (VEPA), a local, community-driven NGO focused on biodiversity conservation, a regional monitoring program is underway to better understand and mitigate the effects of climate change on marine turtle nesting. At the heart of this work is a simple but powerful tool - temperature data loggers - deployed within the sand to track how rising global temperatures are changing the very environment baby turtles are born into.

The Problem with Hot Sand

Sea turtles, such as the Green turtle (Chelonia mydas) and the Hawksbill (Eretmochelys imbricata), are known for their incredible migrations across the Pacific Ocean. When it's time to lay eggs, the females return-sometimes across hundreds of kilometres-to the beaches where they themselves were born. In Vava'u, six known nesting beaches host these events each season.

But in recent years, something has changed. The sands of these beaches, once within a natural thermal range, are heating beyond safe thresholds. And in the case of sea turtles, sand temperature isn't just a comfort factor-it determines the sex of hatchlings. Below 27.7°C, nests tend to produce males. Above 31°C, almost exclusively females.

"Current predictions show that Tonga may be seeing a shift toward a more dominant female population," explains Karen Stone, Director of VEPA. "This kind of imbalance could threaten the long-term survival of turtle populations already under pressure from by-catch, harvesting, and habitat loss."

Monitoring the Nesting Sites

To address this issue, VEPA deployed a series of Tinytag temperature data loggers as part of a regional climate impact study on sea turtle nesting. Initially used to support academic research by PhD candidate Melissa Staines, the loggers are now a key part of VEPA's ongoing conservation strategy and community outreach.

Eight loggers were embedded in the sand across several key beaches, placed carefully into known nesting zones where they remained in situ for 12 months at a time, recording data every 4-6 hours. Field teams return to collect the data every few months, comparing it with surface air temperatures from local weather stations such as the Lupepau'u Airport tower.

"Without these sensors, we simply wouldn't have access to this level of detail," says Karen. "It's one thing to suspect that temperatures are rising-it's another to be able to show the data and track the trends over time."

The Tinytags were selected for their durability and ease of use in remote conditions. With minimal need for internet connectivity or complex calibration, they proved ideal for VEPA's needs-reliable tools in a setting where power and connectivity can be challenging.

From Science to Community Engagement

While the data has research value, VEPA is also using it to drive public awareness and empower local communities. Community ambassadors-trained volunteers embedded in village networks-help communicate the results, tying scientific data back to traditional knowledge and conservation goals.

"This isn't just about collecting data. It's about building a sense of ownership and pride in protecting these animals," says Karen. "We use the logger data in school programs, public talks, and policy discussions."

One of the most powerful narratives VEPA shares is the idea that temperature affects gender-a tangible, real-world impact of climate change that's easy to grasp, and incredibly important. If beaches continue to heat unchecked, turtle populations may collapse under skewed sex ratios, long before other visible effects of climate change appear.

A Shared Ocean, A Shared Responsibility

This work is part of a broader regional effort under the By-catch and Integrated Ecosystem Management (BIEM) program, implemented by the Secretariat of the Pacific Regional Environment Programme (SPREP) and funded by the European Union and Sweden through the Pacific-EU Marine Partnership (PEUMP). VEPA collaborates with Tonga's Department of Environment and Ministry of Fisheries, demonstrating how science, policy, and community action can align for conservation impact.
On World Ocean Day, a Message from the Sand

This Sunday, as we mark World Ocean Day, VEPA's work is a timely reminder that ocean health isn't just about coral reefs or deep-sea fisheries-it begins on the beaches where life emerges. In the case of turtles, the first few inches of sand can determine the future of an entire population.

By embedding simple loggers into these sands, VEPA is telling a powerful story: that local action, community science, and accessible technology can work together to protect marine biodiversity.

"The loggers give us data, but it's the people-our staff, our volunteers, our communities-who turn that data into action," Karen reflects. "That's the heartbeat of conservation in the Pacific."