Drone footage has captured what is believed to be the largest migration of green turtles on film, with 64,000 spotted near Raine Island on Australia’s Great Barrier Reef.
Researchers at Raine Island have used the images, filmed in December, to conduct population surveys of the turtles as they wait to come ashore and lay clutches of eggs.
The scientists had been investigating different methods of research at the world’s largest green turtle nesting site.
Dr Andrew Dunstan, from the department of environment and science (DES) and lead author of the paper said: “Previous population survey methods involved painting a white stripe down the green turtles’ shell when they were nesting on the beach. 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, but eyes are attracted much more to a turtle with a bright white stripe than an unpainted turtle, resulting in biased counts and reduced accuracy.
“Trying to accurately count thousands of painted and unpainted turtles from a small boat in rough weather was difficult. Using a drone is easier, safer, much more accurate, and the data can be immediately and permanently stored.”
The footage was analysed, frame by frame in the laboratory, reducing observer error and allowing accurate counts on 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 new method of counting has found that vessel-based counts are inaccurate, leading to researchers underestimating numbers by a factor of 1.73.