Warming temperatures are turning one of the world's largest sea turtle populations in Australia's Great Barrier Reef almost entirely female, running the risk that the colony may not sustain itself in coming decades, a study has found.
Sand temperatures determine the sex of turtle hatchlings, with warmer temperatures resulting in more females. During the past two decades, temperatures on islands in Australia's northern Great Barrier Reef have increased to the point "that virtually no male turtles are now being produced from these nesting beaches," said researchers from National Oceanic and Atmospheric Administration (NOAA) Fisheries in the US.
The study published in the journal Current Biology "raises new concerns over the immediate threats of climate change to sea turtle populations". The results will be important for wildlife managers as they consider strategies to lower incubation temperatures at key rookeries around the world. This may help "boost the ability of local turtle populations to adapt to the changing environment and avoid a population collapse or even extinction".
Although researchers have known for decades that warming temperatures alter the sex of sea turtle offspring, this is the first time they have directly documented the trend in a major wild population. The study used an innovative combination of endocrinology and genetics to assess the sex of hundreds of turtles across a large foraging ground, revealing the sex ratio of immature and mature turtles from different nesting beaches over many years.
The analysis revealed different sex ratios and trends in two nesting populations in the Great Barrier Reef. Green sea turtles from cooler southern nesting beaches were about 65 to 69 per cent female, testing showed.
Sea turtles from warmer northern beaches leaned even more heavily female, with 86.8 per cent of adult turtles, 99.8 percent of sub-adult turtles, and 99.1 per cent of juvenile turtles turning out to be female. "This has given us an important new window into demographic changes in these populations over the last several decades, which have gone undetected until now," said Michael Jensen, a research biologist at NOAA Fisheries. "The disconcerting thing is that we can now see how changes in the climate could affect the longevity of this and other sea turtle populations around the world," Jensen said.
Green sea turtles are protected under the Endangered Species Act and listed as endangered on the International Union for the Conservation of Nature's Red List. The Great Barrier Reef holds some of their largest populations in the world, researchers said.