SARASOTA, Fla. – Every morning during sea turtle nesting season, which occurs between May 1 and October 31, scientists and citizen volunteers comb 35 miles of shoreline in Sarasota County, Florida.
They look for signs of turtles coming ashore to lay their eggs, or evidence of hatchlings.
They often find tracks leading away from the water, as the bright lights of hotels and condos on the beach confuse the baby turtles and cause them to crawl inland. Experts say about 90% of all sea turtle nesting in the United States occurs on Florida beaches.
Coastal development is the biggest threat to sea turtles right now, according to the Florida Fish and Wildlife Conservation Commission. But scientists say global warming is another emerging risk to the species. This is because, unlike humans, sea turtles do not have sex chromosomes. Their gender is determined by the temperature of their nests.
Hot weather produces females, while cool temperatures produce males
“Warm temperatures will produce more females and cooler temperatures will produce more males. The saying is hot chicks and cool guys,” says Jake Lasala of the Mote Marine Sea Turtle Conservation & Research Program in Sarasota.
This process is called temperature-dependent sexing, and it affects a variety of animals, including crocodiles and some lizards.
Sea turtles that incubate in sand at or below 81.86 degrees Fahrenheit will be male. Those in sand 88.8 degrees Fahrenheit or higher will be female. Anything between this range will produce a mixture of offspring.
According to Florida State climatologist David Zierden, summers in Florida have been warmer for the past two decades, and studies show that for several years now, the vast majority of sea turtle hatchlings are wild females.
This can be good news for male turtles in the short term because they have more mates.
Too many female turtles can lead to a population decline because the males can’t keep up
But scientists like Lasala worry about what climate change could mean for the future of the species. Loggerheads are the most common sea turtles in Florida and are named for their massive block-like heads. They are also among the larger sea turtles, with adults weighing an average of 275 pounds.
“If there are too many females, your population can start to decline because the males can’t keep up with the number of females,” Lasala he says. “If the temperature continues to rise further than what is currently projected, then you will start to see the death of the hatchlings because the eggs cannot develop beyond a certain temperature.”
And Florida isn’t the only area where heat affects the sex of sea turtles.
A 2018 study found that 99% of green sea turtle hatchlings on Australia’s Great Barrier Reef islands were female.
“So it’s not a new thing,” says Lasala. “We’re just seeing it on a larger scale now.”
It may take decades for the full impact of this gender imbalance to be felt. It takes about 25 years for a sea turtle to reach sexual maturity.
Non-profit groups work to protect the nests of this endangered species from predators
While the marine reptiles are still considered an endangered species, Lasala says their numbers are increasing again, largely because state wildlife agencies and nonprofit groups are working to protect the nests from predators and beachgoers.
After excavating a hole and laying about 80-120 eggs, female sea turtles fill the hole with sand and camouflage the nest before returning to the sea. In Florida, these nests are monitored and marked with tape and wooden stakes.
Even so, only 1 in 1,000 hatchlings actually live to adulthood, according to the Florida Fish and Wildlife Conservation Commission.
Back on the beach in Sarasota, marine biologist Alexis Ferrara fields several calls from volunteers who report finding stranded cubs. The baby turtles are then taken to Mote Marine’s Sea Turtle Rehabilitation Hospital for a medical check-up before being released into the Gulf of Mexico – each one a small success story.
And even as the Earth continues to warm, Lasala says, all hope may not be lost.
Over time, sea turtles have learned to adapt to their environment.
Last summer, a female rattler laid her eggs far north of Florida on the cooler sands of the Jersey Shore.