Green turtles in the northern Great Barrier Reef and feminisation
9 January 2018
The study Environmental warming and feminization of one of the largest sea turtle populations in the world raises concerns for turtle researchers, according to Queensland Department of Environment and Science (DES) Chief Scientist Dr Col Limpus.
However, Dr Limpus notes, “This is a brief study of one year’s data of young turtles at one location – the green turtle foraging population of the Howick Group of reefs off Cape York Peninsula.”
“The study shows a shortage of immature turtles and almost no male turtles coming from the northern Great Barrier Reef (GBR) breeding population,” Dr Limpus said.
“That is a worry, because Queensland Turtle Conservation Program research showed the ratio of male turtles was much higher in the early 1990s.
“As part of the Queensland Turtle Conservation Program we have been exploring options for manipulating the nesting beach temperature. We’ve been experimenting at Mon Repos turtle rookery near Bundaberg to establish the importance of shade in regulating nest temperatures.
“Other researchers have done projections on how temperature increases could affect the proportion of male turtles being produced.
“Higher temperatures in the nest—above 28 or 29 degrees—produce more females. Too high—above 32 degrees—and more embryos will die.
“Many scientific papers predict that climate change will be a problem for turtle species. This new study has tried to measure feminisation,” he said.
Dr Limpus said the Raine Island Recovery Project was investigating the feasibility of using ‘artificial rain’ via sprinkles to moisten the beach to improve nesting success and at the same time provide some cooling of the sand.
“Turtles themselves may be trying other things. DES is analysing 50 years of monitoring data from nesting turtles in the southern GBR to assess if there is evidence of the turtles shifting to nest in cooler, more southerly beaches, or if there is evidence of the turtles changing to breed during cooler months of the year,” Dr Limpus said.
Dr Limpus said there were two problems in the northern Great Barrier Reef green turtle population:
- Firstly, for 21 years, hatchling production has been greatly reduced at Raine Island, the main green turtle rookery for the northern GBR green turtle management unit. Researchers knew that the reduced production of hatchlings would lead to a shortage of green turtles feeding in coastal waters—which is what this study is showing. DES has been testing ways to improve hatchling production at Raine Island, with some encouraging results.
- Secondly, there has been a reduction in male green turtle numbers in the northern Great Barrier Reef.
“DES recognises the need to repeat this type of study at other foraging areas for the northern GBR green turtles and across multiple years,” Dr Limpus said.
“The authors mention the need to lower incubation temperatures at key rookeries to help eggs survive and hatch. We acknowledge a solution is complex, and while we are taking action there is no off-the-shelf fix for nest temperatures.
The Raine Island Recovery Project is a collaboration between BHP, the Queensland Government, the Great Barrier Reef Marine Park Authority, Wuthathi and Kemer Kemer Meriam Nation (Ugar, Mer, Erub) Traditional Owners and the Great Barrier Reef Foundation.
The study released on 9 January 2017 is Jensen et al, Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World, Current Biology (2017).