An Australian research team has captured drone footage of 64,000 turtles making a trip to Raine Island in the Great Barrier Reef.
The footage, captured by a research team led by Dr Andrew Dunstan from Queensland’s Department of Environment and Science in December 2019, was used to determine Raine Island’s green sea turtle population. Their findings, published in PLOS One in early June, concluded aerial drone footage was one of the most accurate methods to properly determine populations.
“New scientific research published on Monday 8 June in PLOS One found that drones, or Unmanned Aerial Vehicles (UAVs), were found to be the most efficient survey method,” Dr Dunstan said in a media release.
“Underwater video using a Go-Pro may also be a useful alternative for in-water surveys of turtles.”
According to the Great Barrier Reef Marine Park Authority, there are six species of turtles living in the reef but the green sea turtles remain the most abundant. While there are two stocks living in the region — the southern and northern — it's the northern stock that commutes between Raine Island and Moulter Cay with an average annual nesting population of 30,000 females. A figure which might be disputed by the new drone research.
The drone study follows previous attempts to count the population with more complicated and less accurate methods, such as painting some turtles and attempting to manually count them from a boat.
"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," Dr Dunstan said.
"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 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."
When the researchers compared the estimated tallies from both methods, it was found that the manual counting methods had been underestimating by a substantial amount.
"When we compared drone counts to observer counts we found that we had under-estimated the numbers in the past by a factor 1.73," fellow researcher Richard Fitzpatrick said in a media release.
"By using drones we have adjusted historical data. What previously took a number of researchers a long time can now be by one drone operator in under an hour."
The new estimates will allow the Raine Island Recovery Project — a green sea turtle conservation initiative — to take into account population figures when rebuilding nesting beaches and other constructions designed to protect the population.