Biologists raising baby loggerhead turtles for conservation find disturbing gender trend

December 17, 2002

BEAUFORT, N.C. -- As part of a large-scale project to preserve loggerhead sea turtles, researchers from three institutions have been raising about 1,200 hatchlings though their first months and are now releasing them after identifying the animals' genders.

These ongoing studies are already revealing an unexpectedly small percentage of males among baby turtles collected from Carolina and Georgia beaches, which could have negative implications for the future of the entire Southeastern loggerhead population, the investigators report.

The scientists said this is the first time so many loggerhead hatchlings have been raised and studied so intensely. The research is intended to provide information critical to boosting the numbers of the threatened species. As a bonus, the selected animals are able to avoid the predators hatchlings normally face when they crawl from nest to surf to begin their lives at sea.

"Just as they emerged from the nest, we captured them, packed them in wet sand from their beach and transported them," said Larry Crowder, the Stephen Toth Professor of Marine Biology at Duke University's Nicholas School of the Environment and Earth Sciences.

"The first time they hit the water, it was here," Crowder added, pointing to water-filled tanks at the Duke Marine Laboratory in Beaufort, N.C., where loggerheads still in captivity are being kept in surplus Easter baskets for almost three months.

Scientists, conservationists and students have collected a total of about 1,200 baby loggerheads from 10 beaches as far south as Miami and brought them to the Duke Marine Laboratory, a Florida Atlantic University (FAU) facility at Boca Raton and the Mote Marine Laboratory in Sarasota, Fla.

About 500 of those have passed though Duke after being collected, mostly by volunteer turtle nest monitors, from four beaches in the Carolinas and Georgia. "There was a lot of driving to go get turtles," Crowder said. About 250 of Duke's temporary captives still await release.

"This study has been a massive effort to learn some very critical basic information: how many boys and girls are out there," said Jeanette Wyneken, a FAU assistant professor of biological sciences who is an expert on sea turtle anatomy and turtle conservation.

Wyneken, the project's principal investigator, is supervising the turtle rearing at both Florida institutions. Crowder, the co-principal investigator, heads Duke's effort. The loggerheads are all being grown to the size needed for them to safely undergo minor surgical procedures known as laparoscopies to determine their genders. This involves a small incision to briefly insert a tiny scope and examine the babies' gonads.

"These turtles have very small gonads at this age and are difficult to identify," said Wyneken, who performed the surgeries. "By relying on several different criteria we were able to get the information." Following a two-week recovery period, the turtles are then ferried out from shore to begin their lives at sea in the warm waters of the Gulf Stream. Wyneken and Crowder both noted that safely releasing the animals as winter approaches is almost as much of a challenge as the study itself.

Crowder said this work is part of his 20-year effort to help loggerheads recover from years of human exploitation. Not only have the animals been caught for food, but the air-breathing reptiles also have been trapped and drowned inadvertently in fishermen's nets. Additionally, beach development has deprived the turtles of nesting sites.

In response to research by Crowder and other scientists, the National Marine Fisheries Service now requires commercial fishermen to install turtle excluder devices (TEDs) on their nets. These TEDs appear to have significantly reduced mortalities of juvenile and young adult loggerheads, Crowder said.

The excluders and other conservation measures also appear to have helped reverse declines in the numbers of adult female loggerheads counted at monitored nest sites, at least in their most-southern U.S. range. Only nesting females can be counted, since the males remain at sea.

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 is we have a large and recovering adult loggerhead population in the south that's 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. "The results that we have seen so far are surprising and even alarming."

Another challenge for researchers was feeding the growing numbers of hatchlings in their laboratories. Since no one had tried rearing newly hatched loggerheads in such numbers before, the scientists had to answer such questions as how much food does a baby loggerhead require, recalled Crowder. "We decided to use 10 percent of their body weight per day as a ration," he said.

Another uncertainty was what to feed them. Investigators decided on a menu of mostly shrimp, laced with extra vitamins and minerals. "They just gobbled that down," he added. "And they've grown really rapidly."

As part of the research, which was funded mainly by a $350,000 grant from the U.S. Environmental Protection Agency, the scientists are also conducting growth studies that require repeated measurements of both turtles and their food.

The loggerheads get transported to the sea about three months later than they would have naturally. "We're basically taking them to where they would have been if they hadn't gotten waylaid," Crowder said. "In the process, they probably survive that interval way better than they would have on their own."

In planning their project, the researchers tried to address concerns that they might be interfering with the animals' abilities to migrate. But studies at FAU and the University of North Carolina at Chapel Hill show that even hatchling loggerhead turtles can sense and use the global magnetic field, he added. "So, based on that work, when we plop them into the Gulf Stream we think they'll be able to access the latitude and longitude," Crowder said.

If additional gender results continue to contradict expectations, the scientists will be searching for explanations. "It would be nice if we were looking at a simple system of temperature determining the sex," said Wyneken. "But even if there are no more surprises, it may be that we are looking at a somewhat more complex set of factors." 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."

Duke University

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