Decline in sex-ratio of Green sea turtles

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One of the world’s largest turtle populations is turning almost entirely female, and the cause is most likely warming temperatures in a changing climate.

Cause of decline in sex ratio

The sex of hatchlings in sea turtles — and in a few other species such as alligators and crocodiles —depends on the temperature of the sand in which the eggs incubate, with warmer temperatures resulting in female hatchlings and cooler temperatures in males.

The US National Oceanic and Atmospheric Administration (NOAA) website specifies the temperature ranges that lead to offspring of one sex or the other: male when it is 27.7°C or cooler, female when 31°C or warmer, and a mix of male and female baby turtles when the temperature fluctuates between these two limits.

Difference of ratio in 2 places

Turtles of the northern Great Barrier Reef (GBR) are genetically different from those of the southern GBR. The results of the study, published in Current Biology, showed an alarming female bias in turtles from the northern Great Barrier Reef, which is warmer than the southern GBR: 86.8% female among adults, 99.8% female among subadults and 99.1% female among juveniles.

The fact that the ratio exceeds 99% among the younger turtles from the warmer region, while being 86.8% among adults of the region, indicates that the proportion of females has increased in recent decades.


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