Pacific green sea turtles are on the brink of extinction as rapidly rising temperatures are turning a majority of their entire population into females, new research reveals.
The northern Great Barrier Reef serves as home to one of the world's largest populations of green sea turtles. Unfortunately, this could soon change with an extremely female-biased sex ratio among their stock.
A paper from the National Oceanic and Atmospheric Administration, California State University, and Worldwide Fund for Nature Australia notes an excess of more than 200,000 females in the nGBR.
These figures reflect an extremely skewed ratio of 116 females to one male green sea turtle, with females accounting for 99.1 percent of the northern stock's juveniles, 99.8 percent of subadults, and 86.8 percent of adults.
Although male green sea turtles are known to mate with multiple females, this unhealthy ratio is more dangerous than beneficial. The paper calls for immediate action before such feminization causes a population collapse or extinction.
Warm Sand Temperatures Produce Female Hatchlings
Sea turtles are one of the species with temperature-dependent sex-determination. Nests in cooler sands produce a larger proportion of male hatchlings, while those in warmer sands produce a larger proportion of females.
Furthermore, the paper reveals that the temperature dictating the sex-ratio of hatchlings is also hereditary and its range is quite limited. Only a few degrees Celsius lie between the temperatures producing 100 percent male and 100 percent female hatchlings.
Based on previous records, scientists determined that feminization of Pacific green sea turtles began two decades ago. Sand temperatures were found to be abnormally high around that time due to global warming, causing a large proportion of hatchlings to produce females.
Feminization was then passed on from one generation of green sea turtles to another, until some of their breeding grounds, such as Raine Island and nearby coral cays, became an exclusively female-producing rookery.
A report claims that this is a huge environmental problem. Apparently, the 88-acre Raine Island is one of the biggest green sea turtle rookeries in the world, with up to 18,000 females laying their eggs at once on the island during nesting season.
WWF Australia Urges More Intensive Conservation Efforts
WWF Australia chief executive Dermot O'Gorman has encouraged more intensive and urgent action to save the Pacific green sea turtle population. He pointed out that conservationists have only been using practical methods such as using shade cloths to lower sand temperatures in rookeries.
"The Great Barrier Reef settlement was significant and turtles were under enormous pressure outside Australian waters," he says in a report. "An additional threat to them really does sound alarm bells. Now every large reproductive male is going to be even more important."
Scientists behind the paper will study the GBR's male stock to determine effective conservation strategies, which they plan to implement in the long-term.