The climate crisis has created a huge sex imbalance for Florida’s sea turtles. More frequent and hotter heat waves baking the sand on the state’s beaches means that seemingly every new hatchling is female, turtle researchers told Reuters.
Female sea turtles bury their eggs in the sand along the shore, where the eggs nest for about two months. The sex of the turtles is not determined during or soon after fertilisation; instead the temperature of the sand along the shore helps determine if the turtle will be male or female.
When turtle eggs incubate below 27.7 degrees Celsius, the hatchlings will be male, but eggs incubated over 31 degrees C will hatch female turtles. Summers with fluctuating temperatures are necessary to ensure a mix of both, but Florida summers are only getting hotter under climate change.
Florida researchers pointed to a 2018 Australian study published in Current Biology, in which blood samples from turtles showed that more and more turtle hatchlings were female, especially those whose eggs were on hotter sands. Australian researchers also compared the female population of juvenile turtles to that of older turtles and found more evidence that the male population was declining.
“The frightening thing is the last four summers in Florida have been the hottest summers on record,” Bette Zirkelbach, the manager of the Turtle Hospital in Marathon told Reuters. According to Zirkelbach, many biologists studying the hatchlings “have found no boy sea turtles, so only female sea turtles” for about four years.
Without a decent ratio of male to female turtles, breeding seasons will yield fewer hatchlings that will grow up to replenish endangered turtle populations. There are anywhere from 40,000 to 84,000 nests laid along Florida’s beaches every year, according to the Florida Fish and Wildlife Conservation Commission. But only one in 1,000 hatchlings actually survives to adulthood, and all five species of Florida sea turtles are listed as endangered or threatened.
They’re easy prey for larger animals, like birds, that devour the little hatchlings before they can escape into the ocean. Housing developments are also a threat. The extra artificial light can confuse hatchlings into moving away from the water and toward land, where they’ll become another animal’s snack or die from dehydration. Researchers have also noted more turtles struggling from contagious tumours called fibropapillomatosis, Reuters reported. If untreated, the infected sea turtles will die.
Biologists have noticed the sharp decline in male sea turtles along Florida’s beaches for about a decade. There wasn’t a single male loggerhead sea turtle born on beaches used for research on Florida’s Gulf or Atlantic coasts from 2015 to 2017, Jeanette Wyneken, the director of Florida Atlantic University’s Marine Lab, told Naples Daily News in 2018. Wyneken and other researches would take 10% of the hatchlings from a nest to a lab until they were large enough for researchers to check for their sex.
Previous years also pointed to the increase in female hatchlings compared to male.“There was never a year with a majority of males. The closest was 2013, when we had 68 per cent females,” Wyneken told Reuters.