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Ground-breaking turtle tracker developed at Oxford

Daniel Maloney reports.

Two Oxford PhD students have developed SnapperGPS, a low cost, low power wildlife tracking system the size of a pound coin that has revealed unexpectedly diverse behaviour among turtles.

 As part of their research project, Amanda Matthes and Jonas Beuchert, supervised by Professor Alex Rogers, built a bare-bones receiver for less than $30. The receiver can run for more than ten years on a single coin cell. This is in contrast to existing devices, which are often expensive and come with heavy batteries for long-term deployments. One tag can easily cost more than $1000, which prohibits the study of many animals.

The core aims of SnapperGPS, to make the hardware as simple and energy efficient as possible, were achieved by doing little signal acquisition and processing on the device itself. By creating a web service that processes the signals in the cloud, the physical tag required far less electronic components, allowing it to be made lighter, smaller and cheaper. This concept of processing signals in the cloud is known as snapshot GNSS and has the advantage of requiring only a few milliseconds of signal to locate the receiver. This is key for accurate tracking, as navigation satellite signals cannot travel through water. However, sea turtles regularly come to the surface to breathe. These short windows of opportunity may not always be enough for traditional GPS methods to resolve the position of the receiver. But a snapshot method only requires a few milliseconds of signal which makes them ideal for such marine applications.

The effectiveness of this cheaper, smaller, and low-power tracking solution was tested when SnapperGPS was deployed on nesting loggerhead sea turtles on the island of Maio in Cape Verde. Loggerhead sea turtles spend most of their life in the ocean, but every two to three years mature females come to a beach to nest. They lay several clutches of eggs separated by roughly two weeks, which makes it possible to recover the hardware and any data it captured.

For this initial deployment, the SnapperGPS tags were placed into custom-made enclosures that were tested to be waterproof to at least 100 metres. Unfortunately, due to the COVID-19 pandemic, the tags were deployed late in the nesting season, which negatively affected the recovery rate as many turtles were already laying their last nest when they were tagged.

In total twenty tags were deployed and nine recovered. Some experienced unexpected technical failures but the tags that survived were able to capture several location tracks that showed previously unknown behaviour among turtles.

 The collection of wildlife location tracking data such as this is vital, as it can inform conservation policy decisions that help protect habitats and prevent human-wildlife conflicts. This data provides novel insights into the loggerhead sea turtle population on Maio, which will help to improve anti-poaching measures, as well as identifying important marine habitats that may need special protection. In future however, the unique properties of this tracker could allow for the detailed study of many species, particularly those which are key to ecosystems but are under researched due to a lack of funds, allowing for a more complex understanding of the natural world and more effective methods to protect it.

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