In areas south of Jacksonville, Fla., female loggerhead counts that were declining by 2 percent each year are now increasing at a rate of 4 percent annually, Crowder said. From Jacksonville to the limits of their northern range in North Carolina, however, female loggerhead inventories are still decreasing by up to 3 percent annually.
Scientists are paying special attention to the northern subpopulation of loggerhead hatchlings because it was thought to include more males than females, Crowder said. Such skewed sex ratios can arise because sand temperature plays a strong role in determining the sex of turtles that develop there. Cooler temperatures were thought to favor males.
With most males expected to be hatching in the north, scientists were concerned that when these two separated subpopulations reach reproductive age at sea the result could be a gender imbalance.
"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," said Crowder.
"There may simply not be enough males," added Wyneken. "Additionally, the genetic diversity that this northern group contributes to both the northern and southern subpopulations should not be lost."
While the gender analyses are just beginning, Wyneken's first results have shown that hatchlings from the southern subpopulation are 85 percent female and 15 percent male.
Such gender ratios for loggerheads from the warm southern beaches were no surprise. But Wyneken's initial results for the northern subpopulation -- 60 percent female and 40 percent male -- were unexpected.
"What we're seeing is very few males being produced in the north," said Crowder. "So the situation
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Contact: Scottee Cantrell
scottee@duke.edu
919-613-8074
Duke University
17-Dec-2002