Recent research has revealed that the northern Great Barrier Reef’s green sea turtle offspring are born almost completely female, with males outnumbered by at least 116 to 1. If this feminisation trend continues, it will be detrimental to the future of the species. So, why is this happening?
The sex of a sea turtle is determined by the temperature of the sand incubating the eggs. Warmer temperatures of 29.1 degrees Celsius and above produce females and cooler temperatures produce males.
Increasing temperatures as a result of climate change means more females are born, disturbing the natural gender ratio. It’s possible that the population of sea turtles could be completely female in the near future.
This is of critical concern to the longevity of many marine turtle species. Without males, the species cannot reproduce, and the combination of this with other threats such as poaching, fishing bycatch and loss of habitat, means we are at risk of losing these majestic mariners forever.
What are we doing?
The support of Koala has allowed us to work with partners including the University of Queensland and the Conflict Islands Conservation Initiative to launch a new research project to trial practical methods to cool the sand temperature of sea turtle nests.
Over three months, a range of cooling methods were trialled on Milman Island nesting beach in the northern Great Barrier Reef for both hawksbill and green turtles. These included natural shade from palm fronds and pandanus leaves, artificial shade, seawater irrigation and rainwater.
After months of trials and research analysis, the results from the first phase came in!
Shading and irrigation showed to be successful in cooling nests and producing more male hatchlings. Hatchlings from shaded nests were also faster and more active, which means they have a greater chance of survival 48 hours after emerging from their nests.
As part of the second phase of research, our conservation team visited Heron Island in Queensland where they conducted further experiments to better understand if seawater irrigation is effective at lowering sand temperatures. Here, seawater was found to cool nest temperatures on average by 1.3 degrees. This decrease could mean the difference between producing male and female hatchlings and ensuring the survival of future green sea turtle populations.
Learn more by watching the video below:
The team experienced great success with seawater irrigated nests which led them to the third phase of research: determining how many males are needed to maintain viable green turtle populations.
To do this, the team travelled to Heron Island and conducted underwater and drone surveys to determine the “operational” sex ratio (the ratio of breeding adult males to females) of the reef's southern population of green turtles. They hope they can use this ratio as a model for what a healthy population of green turtles should look like.
Watch this video to learn more about the most recent phase of this important research:
Updates from the field:
Heron Island - Drone field trip report
Heron Island 2021 report
Preliminary results 2019-2020
Milman Island field report