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ScribeBy: The State newspaper
Originally Published on: 12/25/02
CHARLESTON, S.C. - Maybe it's something in South Carolina's water. Biologists at Duke University are studying loggerhead turtles, including about 250 from Kiawah Island and the Cape Romain National Wildlife Refuge, and have found troubling information so far.
The study shows beaches north of Jacksonville, Fla., including those in the Palmetto State, are not producing enough male loggerhead turtles. The hotter the temperature, the more females develop in a nest; the cooler the temperature, the more males emerge.
The lack of males is an ominous sign for a species already threatened, biologists say.
Northern nests, including those in South Carolina, were expected to provide 65 percent males. Instead, the first batch of northern turtles turned out to be 40 percent male.
The second batch was laid later in the spring as temperatures rose and had just 15 percent males.
"It will only get worse. I expect more females," said Larry Crowder, the Duke professor of marine ecology who is co-principal investigator of the first-of-its-kind study.
"The results that we have seen so far are surprising and even alarming," he said.
Crowder said studies have shown turtle eggs start becoming infertile when females outnumber males by five or six to one.
Northern loggerheads are decreasing in population by about 3 percent a year. They have been proposed for re-listing as an endangered rather than threatened species.
Biologist Sally Murphy, sea turtle specialist with the state Natural Resources Department, had studied loggerhead hatchlings in South Carolina and Georgia about 20 years ago. The study found the link between temperature and sex of hatchlings.
Last winter was a mild one, Murphy said, and nesting began sooner than she had ever seen. "It's possible the sand never cooled to the point it would if we had a normal winter," she said.
Duke's Crowder says this year was the second warmest on record. He said temperatures in the Southeast have been rising since 1966. Hotter climates could mean fewer males down the road.
"Warming is a hypothesis we can't exclude," Crowder said.
There are many challenges in the study, Crowder says. It is difficult to determine the sex of hatchlings. Biologists use a laparoscope, then confirm findings through biopsies of tissue samples.
The turtles must also be raised in labs. Each of the 500 is fed 10 percent of its body weight a day. Crowder has only had a casualty rate of 3 to 4 percent.
Crowder hopes the study, which involves about 100 professionals and volunteers, can one day help determine the sex ratio of the Atlantic coast loggerhead population.
"There will be more chapters written," Crowder said.
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