Written by Scarlet
Green Sea Turtles have been found to be 99% female on Ingram Island, the largest Turtle breeding grounds in the world, horrifying scientists who now are having to question the species chances of survival.
Life is hard for the Green Sea Turtle. The International Union for Conservation of Nature lists them as endangered, mostly due to human activity. Between them being hunted for food, their eggs being stolen, pollution poisoning them and being trapped in fishing lines thanks to humans they are slowly dying off. Even their nesting beaches are being destroyed thanks to real estate development.
Things are now getting even harder for them as climate change is warming the seas waters. Unlike humans, a green sea turtles sex isn't determined by its DNA but by the temperature of the turtle nest. At 29.3C they will have equal numbers of males and females, but as it gets hotter the more females will be born. This is known as temperature-dependent sex-determination. Although it is not clear why their sex is linked to local temperature, some biologists hypothesise that it may be due to the fact that turtles in colder conditions tend to grow larger and therefore there may be some benefit for the males to be larger.
In a large-scale research study on Ingram Island, in Queensland, Australia, a team of scientists, for about a month, collected and released turtles and took plasma samples from them as they went. This allowed them to distinguish the young males from females as they look very similar on the outside.
They found that young female green sea turtles now outnumber young males by 116 to 1 and that this trend had been happening for almost 20 years. Biologist David Owens, professor emeritus at the College of Charleston has called it “One of the most important conservation papers of the decade,”. He added: “Climate change is clearly the culprit,” "We're talking a handful of males to hundreds and hundreds of females. We were shocked." Said, co-author of the study, Camryn Allen. "This is extreme—like capital letters extreme, exclamation point extreme,"
While the study does agree that a higher female to male ratio in green sea turtles is advantageous due to their polygynous behaviour it questions what the minimum proportion would have to be to sustain sea turtle populations.
There is also now the question of how much climate change will affect other temperature-dependent sex-determination animals such as iguanas, alligators and inland silversides. Allen and her co-author Jenson now intend to expand their research to other nesting sites, including Guam, Hawaii and Saipan. They also feel that management strategies are possible, for example shading the nesting sites and pouring water onto the sand to cool it may help. Meanwhile, the Raine Island Recovery Programme, along with the Australian government, is working on monitoring and protecting the turtles. You can read the full study here.
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