99% of These Sea Turtles Are Turning Female

Scientists took a survey of Pacific green turtles off Ingram Island in northern Australia. It's not a simple task to determine the sex of a sea turtle, but blood tests for testosterone levels helped. While they expected to find more females than males, the results were pretty shocking.

Since the sex of a sea turtle is determined by the heat of sand incubating their eggs, scientists had suspected they might see slightly more females. Climate change, after all, has driven air and sea temperatures higher, which, in these creatures, favors female offspring. But instead, they found female sea turtles from the Pacific Ocean's largest and most important green sea turtle rookery now outnumber males by at least 116 to 1.
"This is extreme—like capital letters extreme, exclamation point extreme," says turtle scientist Camryn Allen, with the National Oceanic and Atmospheric Administration in Hawaii. "We're talking a handful of males to hundreds and hundreds of females. We were shocked."

Further studies show that the sex imbalance in sea turtles has been there for some time, but it's getting worse quickly. The effect is more pronounced near coral reefs that are dying, and less near healthy reefs. While fewer males than females are needed to continue a species, what happens when there are no males left? Temperature fluctuations affect sex imbalance on other species, too, particularly reptiles and fish. Read about the latest sea turtle research at NatoGeo News.