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As the Earth heats up, male sea turtle hatchlings could become more rare

Mote's sea turtle activities are conducted under Florida Fish and Wildlife Conservation Commission Marine Turtle Permits 155, 216, 027, 054, 070, 048, 126, and 028, and all turtle images were acquired under conditions not harmful to this or other turtles while conducting authorized research.
Jake Lasala
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Mote's sea turtle activities are conducted under Florida Fish and Wildlife Conservation Commission Marine Turtle Permits 155, 216, 027, 054, 070, 048, 126, and 028, and all turtle images were acquired under conditions not harmful to this or other turtles while conducting authorized research.

Each morning during sea turtle nesting season, scientists and citizen volunteers with Mote Marine Laboratory in Sarasota comb 35 miles of shoreline looking for turtle tracks from mothers coming ashore to lay their eggs or evidence that sea turtle hatchlings have emerged.

Florida has the largest aggregation of loggerhead sea turtle nesting in the world.

Thousands of the marine reptiles lay eggs each year and Mote scientists study and tag these endangered and threatened species to help protect their future.

Their biggest threat right now is coastal development and beachfront lighting, which disorients baby turtles causing them to wander inland.

But scientists say a fast-developing risk to the species is global warming.

That's because the sex of sea turtles is determined by the temperature in which their eggs incubate.

"Warmer temperatures will produce more females and cooler temperatures will produce more males. The adage is hot chicks and cool dudes,” said Jake Lasala, a research fellow with Mote Marine's Sea Turtle Conservation & Research Program.

Studies from his colleagues on Florida’s east coast, show that for the past several years, the vast majority of turtle hatchlings have been female.

 Marine biologist Alexis Ferrara marks the date when turtle hatchlings emerged from a nest on Lido Beach in Sarasota
Cathy Carter
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Marine biologist Alexis Ferrara marks the date when turtle hatchlings emerged from a nest on Lido Beach in Sarasota

Sea turtles that incubate in sand that is 81.6 degrees Fahrenheit or lower, will be male. Those in sand that is 88.8 degrees Fahrenheit or higher, will be female. Anything in between that range will produce a mix of offspring.

As Florida’s summers become hotter -- the last four have been the hottest on record -- beach sand is also getting warmer.

Lasala says that can be problematic for many reasons.

“If there are too many females, then your population can start to decline because the males can't keep up with the number of females,” he said. “If the temperature continues to increase further than currently projected, then you will start to see the death of hatchlings because eggs can't develop after a certain temperature."

Lasala says Florida isn’t the only place where the sex of sea turtles is being altered. A 2018 study found that 99 percent of the green sea turtles that hatched on the warmer, northern Great Barrier Reef nesting beaches in Australia were female.

The process is called temperature-dependent sex determination and it affects a variety of animals, including crocodiles and some lizards.

"So, this isn't a new thing,” Lasala said. “It's just we are now seeing it on a larger scale."

It takes about 25 years for sea turtles to reach sexual maturity, so it could be decades before we see the ramifications of hotter temperatures on sea turtle populations.

And for now, data shows that conservation efforts in Sarasota County have produced positive results. Though they are still considered a threatened species, sea turtle numbers have been rebounding.

Back at the beach, biologist Ferrara takes several calls about stranded hatchlings, which will make their way to Mote Marine's Sea Turtle Rehabilitation Hospital before being released back into the Gulf.

 Hatchlings that have not made it to the ocean are evaluated at Mote's Sea Turtle Rehabilitation Hospital before being released into the Gulf.
Hatchlings that have not made it to the ocean are evaluated at Mote's Sea Turtle Rehabilitation Hospital before being released into the Gulf.

But for the long-term implications for survival, researchers like Lasala are stepping up efforts to consider what climate change means to species whose sex is determined by incubation temperatures.

One of the projects underway is looking at the temperature of beach sand in Sarasota County by placing gauges in loggerhead turtle nests to see what the baseline temperatures are, similar to efforts underway on South Florida beaches.

"And then we're trying different modeling methods to look at sea surface temperature and air temperature and precipitation to see which factors affect temperature the most," Lasala said.

He says these other elements play a significant role in the fluctuation of temperature on beach sand, which could keep more of the eggs from producing a majority female population.

But even if the earth's temperature keeps rising, all hope may not be lost for the sea turtle.

The marine reptiles have managed to outlive their contemporaries, the dinosaurs. And scientists say they seem to have a survival instinct capable of a rapid evolutionary response.

In 2018, for the first time in decades, eggs from a loggerhead sea turtle nest successfully hatched far north of Florida, on a beach in Delaware.

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Cathy Carter