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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

There have been plenty of success stories of recovery of sea turtle populations. The Conservancy's green turtle conservation program at Tortuguero, a major nesting spot in Costa Rica, started in 1959 and since then the population has increased sixfold, making the colony the largest in the Western Hemisphere.

Also, one male turtle goes a long way. Sea turtles are polygamous animals and one male will mate with many females. They have a long lifespan of around 50 years, but some species can live longer. Most sea turtles take decades to mature -- between 20 and 30 years -- and females are actively reproductive for about 10 years. Depending on the species, females will nest between two and eight times each season, laying about 100 eggs in each nest.

In Florida, sea turtle nesting activity has seen some ups and downs over the past few years, with a slightly negative trend since 2014. Overall, nest counts recovered significantly from the lows of the 80s and 90s, a result of conservation efforts in more densely populated areas. Nesting varies widely depending on the species and location. This year, researchers on the Gulf Coast and in Palm Beach country also are betting on record nest counts considering the numbers recorded so far.

The Fish and Wildlife Conservation Commission counted 91,451 loggerhead nests in the state in 2018, compared with 86,870 in 2014. But leatherback nests were down at 949 last year, compared with 1,604 in 2014. Green turtle nest reached 4,545 last year, down from 5,895 four years earlier.

Sea turtles hatchlings have never had it easy. Not all eggs in a nest are viable, and only a small share of hatchlings will survive and grow to become adults. The eggs may be dug up by raccoons, foxes or other predators. Those same predators can gobble up the babies as they race to the surf after emerging from their nests. Once in the ocean, they aren't safe: crabs and other marine animals feed on baby sea turtles.

Mature turtles have few natural predators but humans have done a great job in cutting their survival odds significantly. Poaching of the eggs and the killing of nesting turtles for their meat or to make frames for eye glasses or jewelry have depleted populations all over the world. But the greatest threat to sea turtles is fishing gear, as hundreds of thousands of turtles are accidentally caught by trawl nets and on longline hooks.

And now there is climate change. Can they adapt by nesting in cooler beaches? Will female start looking for shadier locations to lay their eggs?

 

"All organisms tend to adapt to their changing environment by evolving through natural selection, but the question is, will turtles adapt as fast as the climate is changing around them?" said Fredric Janzen, an evolutionary biologist at Iowa State University who was one of the first scientists to connect climate change to temperature-dependent sex determination in turtles. In a 1994 study titled "Climate Change and Temperature-Dependent Sex Determination in Reptiles," Janzen found that even a small increase of 1.5 degrees Celsius (2.7 degrees Fahrenheit) was enough to drastically skew the sex ratio of the painted turtles in his research.

In his opinion, changes are occurring faster than they did prior to human influence, and this can potentially -- and fatally -- outpace the ability of some species to adapt.

(c)2019 Miami Herald

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Distributed by Tribune Content Agency, LLC.

 

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