How global warming has affected the birth rate of sea turtles

Camryn Allen, a scientist at the National Oceanic and Atmospheric Administration in Hawaii, did research early in her career on tracking pregnancy in koalas using hormones. She then began using similar methods to help her fellow researchers quickly determine the sex of sea turtles.

You can’t tell what gender a turtle is just by looking at it. For an accurate answer, laparoscopy is often required – an examination of the internal organs of a turtle using a tiny camera inserted into the body. Allen figured out how to determine the sex of turtles using blood samples, which made it much easier to quickly check the sex of a large number of turtles.

The gender of the turtle hatched from the egg is determined by the temperature of the sand in which the eggs are buried. And as climate change drives temperatures around the world, researchers weren’t surprised to find many more female sea turtles.

But when Allen saw the results of her research on Australia’s Rhine Island – the largest and most important nesting area for green sea turtles in the Pacific – she realized just how serious the situation was. The temperature of the sand there rose so much that the number of female turtles began to exceed the number of males by a ratio of 116:1.

Decreased chance of survival

In total, 7 species of turtles live in the oceans of temperate and tropical zones, and their life is always full of dangers, and global warming caused by human activity has complicated it even more.

Sea turtles lay their eggs on sandy beaches, and many baby turtles don’t even hatch. The eggs can be killed by germs, dug up by wild animals, or crushed by other turtles digging new nests. The same turtles who managed to break free from their fragile shells will have to get to the ocean, risking being caught by a vulture or a raccoon – and fish, crabs and other hungry marine life are waiting for them in the water. Only 1% of sea turtle hatchlings survive to adulthood.

Adult turtles also face several natural predators such as tiger sharks, jaguars and killer whales.

However, it was people who significantly reduced the chances of sea turtles to survive.

On the beaches where turtles nest, people build houses. People steal eggs from nests and sell them on the black market, kill adult tortoises for their meat and leather, which is used to make boots and bags. From turtle shells, people make bracelets, glasses, combs and jewelry boxes. Turtles fall into the nets of fishing boats and die under the blades of large ships.

Currently, six out of seven species of sea turtles are considered endangered. About the seventh species – the Australian green turtle – scientists simply do not have enough information to determine what its status is.

New research – new hope?

In one study, Allen found that in a small population of green sea turtles outside of San Diego, warming sands increased the number of females from 65% to 78%. The same trend has been observed in populations of loggerhead sea turtles from West Africa to Florida.

But no one has previously explored a significant or large population of tortoises on Rhine Island. After conducting research in this region, Allen and Jensen made important conclusions.

Older turtles that hatched from eggs 30-40 years ago were also mostly females, but only in a 6:1 ratio. But young turtles have been born more than 20% female for at least the past 99 years. Evidence that rising temperatures were the cause is the fact that in the Brisbane area of ​​Australia, where the sands are cooler, females outnumber males by a mere 2:1 ratio.

Another study in Florida found that temperature is just one factor. If the sands are wet and cool, more males are born, and if the sands are hot and dry, more females are born.

Hope was also given by a new study conducted last year.

Long term sustainability?

Sea turtles have existed in one form for over 100 million years, surviving the ice ages and even the extinction of the dinosaurs. In all likelihood, they have developed many survival mechanisms, one of which, it turns out, could change the way they mate.

Using genetic tests to study a small group of endangered hawksbill turtles in El Salvador, turtle researcher Alexander Gaos, working with Allen, found that male sea turtles mate with multiple females, with about 85% females in their offspring.

“We found that this strategy is used in small, endangered, highly declining populations,” says Gaos. “We think they were just reacting to the fact that the females had so little choice.”

Is there a possibility that this behavior compensates for the birth of more females? It is impossible to say for sure, but the fact that such behavior is possible is new for researchers.

Meanwhile, other researchers monitoring the Dutch Caribbean have found that providing more shade from palm fronds at nesting beaches cools the sand noticeably. This can greatly help in the fight against the current crisis of the sex ratio of sea turtles.

Ultimately, the researchers find the new data encouraging. Sea turtles may be a more resilient species than previously thought.

“We may lose some smaller populations, but sea turtles will never completely disappear,” Allen concludes.

But it’s important to understand that turtles may need a little more help from us humans.

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