Recently we reported that nearly 99% of Green Sea Turtles on Australia’s Great Barrier Reef were being born female. That study looked at one of the world’s largest nesting areas, with nearly 200,000 turtles.
Of those turtles from beaches at the northern part of the reef (areas with the warmest temperatures) nearly all the eggs hatched were females. With turtles from beaches further south along the reef (cooler temperatures) the percentage of females was closer to normal, about 65-69%. (photo – WWF)
Now Florida’s Sea Turtles are Overwhelmingly Female!
Now new research, as reported in USA Today, indicates that the same phenomenon has been occurring on the beaches in Southern Florida for the last decade. On both the Atlantic and Gulf coast, beaches were sampled and showed that not a single male loggerhead hatchling was found between 2015 and 2017, in fact in seven of the past 13 years there have been no male hatchlings.
Other sea turtle species are showing the same alarming trends. Leatherback turtles are between 80-85% female; while Green Sea Turtles are nearly 95% female. (photo – © Michele Westmorland)
“I can’t say that our data represents what’s going on at 100 percent of Florida’s beaches,” said Jeanette Wyneken, a biologist from Florida Atlantic University, “but we’re looking for trends. And I feel confident those trends are going on at a lot of beaches.”
“The real problem will be if we have one, two or three decades with no males” Wyneken warned.
Warmer Sand on Warmer Beaches
As is the case in Australia the problem is warmer sand on warmer beaches. For turtles, gender is determined by the heat of the sand in which the eggs are buried. Generally, the warmer the temperature the more female hatchlings.
“If a nest is really hot, say 88 degrees, it’s going to be all females,” Wyneken said. While if the nest was in sand at 77 degrees then all hatchlings would most likely be male. These summers, “In Florida, there are very few years where it’s cool enough to produce males,”
The Numbers Add Up!
The reason that slightly fewer Florida leatherback turtles are female is because they are the first to nest in the spring, when the sand is cooler. Loggerheads unfortunately nest during the warmest months and have no male hatchlings. Green Sea Turtles have about 5% males because they nest when the beaches are beginning to cool off in August and September.
A Slight Natural Adaptation
The turtles seen to sense something is not quite right and are slowly adapting, by either laying their eggs earlier, when temperatures are cooler, are later in the season when rains cool the beaches. However, Sea Turtles do not easily adjust where they nest, that trait is probably inborn, so they can’t just go to beaches further north. Plus, the beaches along the Atlantic coast of Georgia, South Carolina and North Carolina are just as warm as Florida’s beaches. “we found more males in Florida than on the beaches up north,” said Wyneken.
In addition to gender, climate change may also be affecting the number of hatchlings emerging from the nests. In overly, dry summers, instead of the usual 70-80% of eggs hatching there may only be 30-40% hatching out. (photo – people.ucsc.edu. )
Will there be enough males?
Fortunately, there are still enough males to go around, maintaining genetic diversity. “But we don’t know how long that will last,” Wyneken added, “because we don’t know how old the males are and how long they can keep breeding.”
Because sea turtles require 25-35 years to reach sexual maturity this gives a little time to resolve this problem. Shading turtle nests has been tried in Australia and may also work in Florida, however that is really only a short term solution.
Wyneken suggests “The big answer is a hard one…. cut down on greenhouse gases that cause climate change. We’ve got to keep the world from getting hotter.”
By Robert Frerck, Blue Ocean Network
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