Loggerhead Crisis Brewing?

Surprising Study Results Show More Females Than Males Hatching in Northern Population p.3

As strange as it may seem, it is the nest temperature that determines whether a boy or a girl turtle hatches out of the egg. Scientists have believed that if the nest is no warmer than 84 degrees Fahrenheit - as you would expect in the Carolinas and Georgia - then most of babies will be boys. If the temperature is warmer - such as you might find on the Florida beaches - you get girls.

Based on this theory, Crowder said, he and Wyneken expected to find that the northern beaches provided more males to mate with the southern females that hatched on the Florida beaches.

When Wyneken started putting together the results from the laparoscopies, she found just what she expected from the southern population: the hatchlings were 85 percent female and 15 percent males.

But she got a shock when the numbers started rolling in from the northern group: initial findings showed that the females outnumbered the males 60 percent to 40 percent.

"What we're seeing is very few males being produced in the north," said Crowder. "So the situation is we have a large and recovering adult loggerhead population in the south that is increasing at 4 percent a year but is producing almost 90 percent females. And we have a northern population that is still in decline and isn't producing nearly the percentage of males as we thought it was.

"So if we lose this northern subpopulation, which is still in decline despite all we've done, it has potential ramifications for the entire regional population."

"There may simply not be enough males," said Wyneken. "Additionally, the genetic diversity that this northern group contributes to both the northern and southern subpopulations should not be lost."

Crowder and Wyneken are just beginning to sort through all the implications and questions that these results raise. They hope to bring another round of baby loggerheads to the Beaufort and Florida facilities this summer to start building on the data they are now compiling.

"By seeing those really skewed sex ratios, we may be looking at a crisis that is not going to show up for 20 years when there aren't enough males to go around," Wyneken said. "Or we may be looking at a really interesting mating system - if it is normal - to have one male for every 10 females." So, they need to verify their results.

Crowder said that there are several avenues that this type of research can take.

One possibility, Crowder said, is "we'll have to start thinking about global warming and climate change. There are a whole string of other possibilities that we are going to consider."

Scottee Cantrell is director of communications for the Nicholas School. Monte Basgall, Duke News and Communications, contrbuted to this article.

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