Global warming may not be so bad for sea turtles — at least, not at first. One of the quirks of sea turtles, along with many other reptiles, is that temperature determines the sex of their offspring. At around 84.2 degrees Fahrenheit (29 degrees Celsius) the ratio of males to females is fairly even, but as temperature rises, more and more hatchlings end up as females. Researchers from Swansea University in Wales calculated how that will change for one major population of sea turtles as the globe warms over the next century, and while they found that it would mean a growing population at first, eventually there will be too few males around.
"The possibility of sea turtles becoming extinct is not a far-fetched scenario."Their research, which is being published today in Nature Climate Change, was focused on a population of loggerhead turtles in Sal, Cape Verde, an island to the west of Northern Africa. For the past 150 years, the temperature there has put the number of female hatchlings laid on light-sand beaches between roughly 50 and 70 percent of those born. Right now, the population of Sal is beginning to see a distinct uptick in the number of females, and the researchers believe that will steadily increase to around 80 percent of hatchlings on light-sand beaches in 2050 to about 98 percent by 2100.
"The possibility of sea turtles becoming extinct is not a far-fetched scenario," Graeme Hays, Swansea's aquatic biology chair, says in a statement. Even though the sex ratio will tip heavily toward females at Sal in the near future, male turtles' tendency to mate more often means that the population should be able to continue growing for a while. But eventually, the researchers say that human intervention will likely be necessary to cool the turtles' nests to ensure that males are brought into the population.
"Eventually a point will be reached when there are insufficient males to fertilize all eggs," they write. "Ultimately if males are so scarce that egg fertility is compromised, management intervention will be needed. Translocating nests from dark beaches to [cooler] light beaches could be a strategy to produce more male hatchlings. Another strategy would be to shade nests (for example, with beach vegetation) to lower incubation temperatures."
Though the paper only focuses on Sal, the researchers say that it can be repeated just about anywhere — and may need to be in order to monitor the safety of populations. The researchers also warn that warming isn't likely to be the only big impact on sea turtles over the next century: in particular, rising sea levels could lead to the destruction of the beaches where they mate. Still, the researchers' estimates show a striking example of how changing climates can impact a population. For these loggerhead turtles, it's perhaps for the better at first, but only for so long.