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Climate change is turning sea turtles female

ByUrsula Dallman

Jan 22, 2018

Climate change has many consequences on the environment around us. Desertification, the melting of glaciers and rising sea levels all spring to mind, but what you may not have considered is that climate change is causing an abundance of female turtles.

A recent study in the journal Current Biology has found that rising sea temperatures are creating a gender imbalance among the green sea turtles in a Great Barrier Reef population. This could have devastating effects on the population’s future, and not just on the green sea turtles themselves but also on their ecosystems.

Research conducted on Ingram Island, in Queensland, Australia found that female sea turtles now outnumber their male counterparts by at least 116 to 1.

Similarly, it appears that the nearby Raine Island has been producing almost exclusively female turtles for 20 years. Out of a northern population of 200,000 turtles, scientists found that 99.1 per cent of hatchlings and 86.8 per cent of the entire population was female.

But why do rising sea temperatures have this effect?

Sea turtles are one of the species with temperature dependent sex-determination. At 29.3C (84.74F) turtle nests produce equal numbers of males and females. The proportion of female hatchlings increases when nests are in warmer sands. Average temperatures have increased by 0.8C (33.44F) around the world since 1880, much of this in recent decades, according to Nasa’s Goddard Institute for Space Studies.

If 29.3C (84.74F)  is exceeded, only female hatchlings will emerge.

Populations of other temperature dependant sex-determination species such as alligators and iguanas could also find themselves in danger if temperatures continue to rise.

Such research has never been undertaken before, because identifying a sea turtles gender is surprisingly difficult. Flipping turtles onto their backs and inspecting them does not reveal their gender, and, due to its lack of sex chromosomes, neither does studying their DNA. Incisions must be made to take a blood plasma sample and examine its hormones.

Proof that this female domination in sea turtles is temperature related can be found on the southern reef near Brisbane. Here, the temperatures are much cooler, the corals remain far healthier and female turtles only outnumber males 2 to 1. However, it is difficult to conclude whether climate change is causing temperature to change.

Temperature can be affected by many local factors, such as sand cooling rain, shade from leaves of trees and narrow beaches forcing sea turtles to nest closer to the water. This helps maintain a larger number of male hatchlings. That is why locations such as Raine in the Great Barrier Reef are more useful in this study as the beaches offer no shade; the link between climate change and sex ratios is more easily identifiable.

It is also difficult to determine the extent of damage to populations where most of the population is female. Male sea turtles often mate more frequently, with more than one female. Therefore, a small female bias is preferable and the ratio of females to males is on average 3 to 1. But is the recent change too much? Potentially. It will take several years to really see the damage caused to the population as turtles only reach breeding age between 25 and 35.

Will there be enough males by then to sustain the population? If we implement management strategies such as shading beaches, and reduce the extent of climate change, we need never find out.

Image credit: 12019 via Pixabay

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