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Warming ocean water is turning 99 percent of northern Great Barrier Reef sea turtles female; population viability threatened

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  • Rising temperatures are skewing population ratios toward extreme imbalance
  • Green sea turtle embryos develop as male or female depending on the temperature at which they incubate in sand
  • In the cooler southern Great Barrier Reef, 67 percent of hatched juveniles were female. But more than 99 percent of young turtles hatched in sand soaked by warmer waters in the northern Great Barrier Reef were female — with one male for every 116 females.
By Laurel Hamers January 8, 2018  Read full ScienceNews article here

Warming waters are turning some sea turtle populations female — to the extreme. More than 99 percent of young green turtles born on beaches along the northern Great Barrier Reef are female, researchers report January 8 in Current Biology. If that imbalance in sex continues, the overall population could shrink.

Green sea turtle embryos develop as male or female depending on the temperature at which they incubate in sand. Scientists have known that warming ocean waters are skewing sea turtle populations toward having more females, but quantifying the imbalance has been hard.

The sex ratio in the overall population is “nothing out of the ordinary,” with roughly one juvenile male for every four juvenile females, says study coauthor Michael Jensen, a marine biologist with the National Oceanic and Atmospheric Administration in La Jolla, Calif.

But breaking the data down by the turtles’ region of origin revealed worrisome results. In the cooler southern Great Barrier Reef, 67 percent of hatched juveniles were female. But more than 99 percent of young turtles hatched in sand soaked by warmer waters in the northern Great Barrier Reef were female — with one male for every 116 females. That imbalance has increased over time: 86 percent of the adults born in the area more than 20 years ago were female….

Michael Jensen, et al. Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World.  Current Biology. Volume 28, Issue 1, p154–159.e4, 8 January 2018 DOI: http://dx.doi.org/10.1016/j.cub.2017.11.057/

“Combining our results with temperature data show that the northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete feminization of this population is possible in the near future.”

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