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Climate change is turning Florida's sea turtles female. How long can these species survive?

Adriana Brasileiro, Miami Herald on

Published in News & Features

MIAMI -- Two dozen tiny leatherback turtles swam around in small tanks, attached by fishing lines to a system that kept them from hitting walls and hurting themselves. As an open-water species, leatherbacks don't recognize barriers, so they are kept on leashes at Florida Atlantic University's lab at Gumbo Limbo Nature Center in Boca Raton.

It was lunchtime and professor Jeannette Wyneken was feeding them a concoction she perfected over the years: organic gelatin, fish oil, protein and vitamins, shaped into little squares. Leatherbacks are picky eaters, feeding mostly on jellyfish.

Wyneken planned to fatten the baby turtles for a few weeks, until they are about the size of her palm and can undergo a laparoscopy to check their otherwise imperceptible gender -- a process that requires inserting a tiny camera to view internal organs. Dozens of hatchlings will go through Wyneken's lab this nesting season as part of her long-running turtle sex-ratio research in South Florida.

Yet even before any testing is done and the hatchlings are released back into the ocean, the scientist already knows there is a strong chance most of the turtles will be one gender: female.

As is the case with some reptiles, the sex of sea turtles is determined by the temperature of the sand where the eggs incubate. With climate change turning up the heat in South Florida, producing longer and hotter summers, sea turtle gender balance is being thrown way out of whack.

"It's scary," Wyneken said. "I'm seeing more and more all-female nests, and even when we have males, it's a very small percentage."


Wyneken's research over the past 20 years shows that the number of males is decreasing across the three species she monitors, even as they lay eggs at different times during the March-October nesting season. Using the past decade as a reference, she said that seven out of the 10 years produced 100% female hatchlings. The three years in which nests produced males, the ratios ranged from just 10 to 20%.

In addition to the leatherbacks, the world's largest sea turtle species, Wyneken tests the genders of loggerheads and green turtles in Boca Raton, Juno Beach and Sanibel Island, where nesting activity is closely monitored and temperatures in nests are tracked year-round.

What happens on Florida beaches is important for sea turtle populations: it's the only state in the continental U.S. where leatherback turtles regularly nest; it hosts some of the world's largest nesting aggregations of loggerheads; and it's home to the second-largest number of green turtle nests in the Western Atlantic Hemisphere, according to the Florida Fish and Wildlife Conservation Commission.

In theory, sex ratios among leatherback turtles, which lay eggs early in the season before the height of the summer in South Florida, should be more balanced than that of loggerheads, which usually start nesting in June and whose eggs incubate in the hottest months of the year. And green turtles tend to lay eggs later, when beaches are beginning to cool in late August and September, so more males should hatch from their nests compared with the other two species.


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