BOCA RATON – A new Florida Atlantic University study discovered that there could very well be too many female sea turtles.

Sea turtles don’t have an X or Y chromosome, unlike a human baby, so their sex is defined during embryo development, and can be greatly altered by changes in the environment. Warmer temperatures during incubation lead to a higher proportion of females while cooler conditions result in more males.

The study, published by Endangered Species Research, found that conditions such as heavier rains and temperature shifts are impacting loggerhead sea turtle sex ratios, potentially influencing future reproduction rates for the species.

“The shift in our climate is shifting turtles as well, because as the temperature of their nests change so do their reproduction patterns,” said Jeanette Wyneken, Ph.D., professor of biological sciences in FAU’s Charles E. Schmidt College of Science. “The nesting beaches along Florida’s coast are important, because they produce the majority of the loggerhead hatchlings entering the northwestern Atlantic Ocean.”
Loggerhead turtles are already fighting an uphill battle since roughly one in 2,500 to 7,000 sea turtles make it to adulthood. The typical loggerhead produces about 105 eggs per nesting season and would have to nest for more than 10 nesting seasons over the span of 20 to 30 years just to replace herself and possibly one mate. And, if enough males aren’t produced because of climate changes, then this will result in a dire problem for this species.
“If climatic changes continue to force the sex ratio bias of loggerheads to even greater extremes, we are going to lose the diversity of sea turtles as well as their overall ability to reproduce effectively. Sex ratios are already strongly female biased,” Wyneken said. “That’s why it’s critical to understand how environmental factors, specifically temperature and rainfall, influence hatchling sex ratios.”
Wyneken and her team documented rainfall and sand temperature relationships as well as rainfall, nest temperatures and hatchling sex ratios at a loggerhead turtle nesting beach in Boca Raton. Nesting season, which runs from April through October, were sampled across 2010 and 2013. The researchers used temperature data loggers in the sand at three locations and buried them at three different depths to create temperature profiles of the sand column above the level that would directly influence eggs. The rainfall data were graphed in temporal synchrony with sand temperature for each depth.
Nest temperatures were recorded throughout incubation. Rainfall data collected concurrently with sand temperatures at different depths showed that light rainfall affected only the surface sand; effects of the heaviest rainfall events tended to lower sand temperatures, however, the temperature fluctuations were very small once the moisture reached upper nest depths.
Nest temperature profiles were synchronized with rainfall data from weather services to identify relationships with hatchling sex ratios. The sex of each turtle was verified laparoscopically to provide empirical measures of sex ratios for the nest and the nesting beach.
“The majority of hatchlings in the sampling were female, suggesting that across the four seasons most nest temperatures were not sufficiently cool to produce males,” Wyneken said. “However, in the early portion of the nesting and in wet years, nest temperatures were cooler, and significantly more males hatched.”
The work was supported, in part by the National Save the Sea Turtle Foundation, Save our Seas Foundation and donations to the Nelligan Sea Turtle Support Fund.