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Drone footage shows 64,000 green turtles migrating to Cairns rookery

The footage showed up to 64,000 green turtles around the island waiting to come ashore on Raine Island and lay their clutches of eggs.

This is almost twice as many green sea turtles coming in to lay eggs as previously believed.

Dr Andrew Dunstan, from the Department of Environment and Science (DES), said researchers had been investigating various ways of measuring the turtle population.

“We were underestimating that a lot,” Dr Dunstan told the CNN news channel.

“We’re finding 1.73 times as many turtles with the drone and as we do when we directly compare with observer counts.

“The team can now go back and adjust the historic population estimates.”

According to the Great Barrier Reef Marine Park Authority, green turtles are found in tropical, subtropical and temperate waters around the world.

They are the most abundant of the six species of marine turtle found in the Great Barrier Reef World Heritage Area.

Found in sub-tidal and intertidal coral, as well as rocky reefs and seagrass meadows, they eat algae, seagrass, mangrove fruit and jellyfish.

A research paper published on June 8 shows that using drones is now the best way to count the sea turtles.

“Previous population survey methods involved painting a white stripe down the green turtles’ shell when they were nesting on the beach,” Dr Dunstan said.

The migration patterns of green sea turtles.

The migration patterns of green sea turtles.Credit:Great Barrier Reef Marine Park Foundation

Researchers then looked for the white stripe when they swam around later, Dr Dunstan said, adding that “the paint is non-toxic and washes off in a couple of days”.

“From a small boat, we then counted painted and non-painted turtles.

“Trying to accurately count thousands of painted and unpainted turtles from a small boat in rough weather was difficult.

“Eyes are attracted much more to a turtle with a bright white stripe than an unpainted turtle and that resulted in biased counts and far reduced accuracy.

“Using a drone is easier, safer, much more accurate, and the data can be immediately and permanently stored.”

The researchers used Go-Pro cameras to survey the turtles underwater, with the drone vision analysed, frame by frame, in the laboratory.

This reduced the observer error rate, reduced the time to count the turtles and allowed accurate counts of the painted and unpainted turtles.

“The ratio of unpainted and painted turtles allowed us to estimate the total population for last December to be 64,000 green turtles waiting to nest on the island,” Dr Dunstan said.

The drone survey is part of the five-year, $7.95 million Raine Island Recovery Project.

It is a collaboration between BHP, the Queensland Government, the Great Barrier Reef Marine Park Authority, the Great Barrier Reef Foundation and the region’s traditional owners: the Wuthathi and Kemer Kemer Meriam people.

Great Barrier Reef Foundation managing director Anna Marsden congratulated the researchers.

“We’re seeing the world’s largest aggregation of green turtles captured in these extraordinary drone images, which are helping to document the largest turtle numbers seen since we began the Raine Island Recovery Project,” Ms Marsden said.

“Raine Island is the world’s largest green turtle nesting site and that’s why we’re working with our Raine Island Recovery Project partners to protect and restore the island’s critical habitat.

“We’re taking action to improve and rebuild the island’s nesting beaches and building fences to prevent turtle deaths, all working to strengthen the island’s resilience and ensure the survival of our northern green turtles and many other species.”

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