Last updated February 23, 2018 at 3:31 pm
Male green sea turtles have all but vanished from the northern Great Barrier Reef with a new study finding that more than 99 per cent of the 200,000 turtles living there are female. Researchers say global warming is the culprit.
Sea turtles’ sex is determined by the incubation temperature of the eggs with warmer temperatures skewing towards females.
The trend is a clear threat to the future of the species.
Understanding the gender balance of newer populations of green sea turtles has been challenging because it’s difficult to determine at nesting grounds where it would require sacrificing live hatchlings, and sampling bias in only examining dead hatchlings.
Until now, sampling foraging grounds has provided easier access to sampling but with mixed populations it has been difficult to assess which regions the turtles originated from.
For the first time, researchers have linked “individuals of known sex sampled within a foraging ground to their natal rookeries using genetic analysis and determine sex ratios produced at regional rookeries,” as stated in their research article published today.
This data gathered from the Howick Group of Island in the northern Great Barrier Reef is a common foraging ground for turtles from both the north and south of the Great Barrier Reef.
It provides insight from over 400 turtles to estimate the sex ratio of populations from the north and south, as well as at different ages.
Their research shows that the young populations are nearly entirely female. The southern Great Barrier Reef turtles at this common foraging ground showed a moderate female sex bias, between 65 per cent to 69 per cent female.
Even more shocking is that the bias in the northern turtles is so extreme that they found 99.1 per cent of juveniles, 99.8 per cent of subadult, and 86.8 per cent of adult-sized turtles were female.
Green sea turtles are already an endangered species with threats from fishing nets, plastic bags and rubbish in the ocean, loss of habitat, and illegal hunting and trade. The effect of global warming is now skewing their population and threatening them even more.
This study suggests that northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete loss of males in this population is possible as well as the loss of their species in this region.
This research was published in Current Biology: www.cell.com/current-biology/comments/S0960-9822(17)31539-7