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Scientists are worried about what climate change means for marine reptiles

STEVE INSKEEP, HOST:

With one of the subtleties of climate change - this is not a wildfire or a storm. It is a change in the weather that affects wildlife in Florida. Record heat there encourages the breeding of more female sea turtles and fewer males. This story explains how the heat affects turtles' gender and also why it matters. Here's Cathy Carter from our member station WUSF in Tampa.

CATHY CARTER, BYLINE: Each morning from May to the end of October, which is Florida's sea turtle nesting season, scientists and volunteers comb 35 miles of shoreline in Sarasota County. They look for turtle tracks from mothers coming ashore to lay their eggs or evidence that baby hatchlings have emerged.

ALEXIS FERRARA: So we're just going to go and look for the nest that hatched.

CARTER: That's marine biologist Alexis Ferrara. When she gets to the nest, she crouches down and finds a hole in the sand.

FERRARA: So I can see the tracks coming out of this one. Hopefully, they've made it to the ocean.

CARTER: Sometimes, the bright lights of hotels and condominiums on the beach confuse the baby turtles, and they crawl away from the sea. Scientists say coastal development is the biggest threat to sea turtles right now. But they say global warming is another risk to the species. That's because, unlike humans, sea turtles don't have sex chromosomes. Their gender is determined by the temperature of their nests.

JAKE LASALA: Warmer temperatures will produce more females, and cooler temperatures will produce more males. The adage is hot chicks and cool dudes.

CARTER: That's Jake Lasala. He's with Mote Marine Sea Turtle Conservation & Research Program in Sarasota. And he says Florida's beaches are home to more loggerhead turtle nests than any place in the world. And studies of the state's sea turtle population show that over the last several years, the majority are female. As Florida's summers become hotter - they've been trending warmer for the past two decades - the beach sand where these eggs incubate has also heated up. And Lasala says that's concerning.

LASALA: 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. If the temperature continues to increase further, then you will start to see the death of hatchlings because eggs can't develop after a certain temperature.

CARTER: And he says Florida isn't the only area where heat affects the sex of sea turtles. A 2018 study found that 99% of the green sea turtle hatchlings on the islands of Australia's Great Barrier Reef were female.

LASALA: So this isn't a new thing. It's just we are now seeing it on a larger scale.

CARTER: It could be decades before the full impact of this gender imbalance plays out. It takes about 25 years for a sea turtle to reach sexual maturity. And while the marine reptiles are still considered a threatened species, their numbers have been rebounding. That's because state wildlife agencies and nonprofit groups have been working to protect nests from predators and beachgoers.

FERRARA: Hey. My patrollers have a hatchling that was found by the Ritz.

CARTER: Back onshore, biologist Ferrara takes several calls about stranded hatchlings.

FERRARA: They are going to meet you at the pavilion to give it to you.

CARTER: The turtles are given a health checkup before being released into the Gulf of Mexico - each a tiny success story. And even if the Earth keeps getting warmer, Lasala says all hope may not be lost. He says sea turtles have a strong survival instinct. This past summer, a female loggerhead laid eggs far north of Florida on the cooler sands of the Jersey Shore.

For NPR News, I'm Cathy Carter in Sarasota, Fla. Transcript provided by NPR, Copyright NPR.

Cathy Carter