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Climate Change Skews Ratio of Female to Male Sea Turtle Hatchlings

New research finds Loggerhead Sea Turtle populations are becoming female-dominant as rising temperatures skew temperate sex determination.

The Loggerhead Sea Turtles of Cape Verde have undergone an unnatural phenomenon in recent years—an increasing majority of hatchlings are female. Dr. Lucy Hawkes, an ecologist at the University of Exeter has recently published a paper which found that, “eighty-four percent of current hatchlings are female and warmer temperatures will increase this proportion.”

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A Sea Turtle hatchling nears the water. Credit: Island Conservation

This is a worrisome trend because a disproportionate ratio of males to females means less reproduction, which can very quickly lead to the death of a species. Considering that Cape Verde hosts 15% of the Earth’s nesting population of Loggerhead Sea Turtles, this could have a disastrous effect on the global population and surrounding environment.

As the earth gets hotter, turtle hatchlings worldwide are expected to skew dangerously female, scientists predict, making the animals an unwitting gauge for the warming climate.”

Danielle Paquette, Washington Post

How to does climate change impact sex determination in sea turtles?

In most species, the sex of the offspring is decided by the process of genotypic sex determination where the information contained in the sex chromosomes of the parents determines the embryo sex. However, in some species of reptiles produce male and female hatchlings through a form of environmental sex determination called temperature dependent sex determination where temperatures within the nest—specifically the incubation temperature of the eggs—influence sex differentiation.

Baby Green Sea Turtles swimming. Credit: Papahānaumokuākea Marine National Monument

According to the National Oceanic and Atmospheric Administration, sea turtles have been observed to produce male hatchlings if the eggs are incubated below 81.6 degrees Fahrenheit and female hatchlings above 87.8 degrees Fahrenheit. Temperatures in between these extremities will produce a mix of male and female baby turtles.

It is not clear how long it will take the population to decline if males stop being produced, as the reproductive lifespan of males is not known – so older males may continue breeding for many years after new males stop being hatched,” explained Hawkes.

Researchers have noticed this trend with sea turtle populations all over the world. Populations in Florida, Australia and Southern California are also showing dramatic sex imbalances, with their turtle populations skewing female by 90%, 99% and 78% respectively. If these trends continue, researchers predict that fewer than 1% of sea turtles born will be male by the end of the century. If global warming continues to escalate, higher temperatures could wipe out the entire species.

Sea Turtles play important roles in both marine and terrestrial ecosystems, making conservation and population preservation vital for global biodiversity. There are seven species of sea turtles, all of which are considered threatened to some extent by various factors including climate change, predation by invasive species, pollution, and unsustainable fishing practices.

Sources:
The Washington Post
National Oceanic and Atmospheric Administration
University of Exeter

Featured Image: Sea Turtle hatchlings scurry across the sand after release. Credit: Mahinda Rajapaksa

About Nicholas Scott

Nick is an undergraduate Marine Biology student at the University of California, Santa Cruz. Having spent his life exploring the ocean on California’s coast, he developed a passion and respect for it, that demanded him to pursue his interest in conservation. Volunteering for the communications team allows him to further his interests and gain more insight as to how to resolve the state of the world around us. In his spare time, Nick enjoys surfing, swimming, and spending time with friends.

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