Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 31, Number 7;   July, 2004

Nesting Turtles and Rebuilt Beaches

By this time of year, a renourished 1.5-mile stretch of beach here should have 15 to 20 turtle nests. But it has just two nests, said Boca Raton's sea turtle program marine conservationist, Kirt Rusenko.

For years scientists throughout Florida have been stumped as to why sea turtles don't like to lay eggs on newly built beaches that are created with sand dredged from the ocean bottom.

"That's the $64,000 question," said R. Erik Martin, the scientific director of Ecological Associates, a consulting firm in Jensen Beach. "In some cases, it may take two years for the nesting to recover."

Rusenko has come up with a theory that could contribute to the understanding of turtle behavior, as well as help in the shaping of public policy for beach restoration. Since 2002, beaches have been reconstructed with dredged sand in Delray Beach, Jupiter, Palm Beach and Fort Pierce.

Rusenko first noticed the dearth of sea turtle nests after Boca Raton rebuilt another beach in 1998. After sufficient rainfall, the turtles returned, he observed.

He wondered if the dredged sand contained too much salt for the leatherbacks, loggerheads, and green sea turtles that lay their eggs in South Florida between March 1 and Oct. 1.

Biologists had assumed that sea turtles rejected new beaches as too compacted, too steep, or too far away from the ocean. The question of saltiness in Florida's sugar sand had rarely occurred to scientists.

"That's really interesting," said Paul Davis, environmental program supervisor for Palm Beach County. "It's certainly worth looking into."

Rusenko is now tracking the salinity of the sand on Boca Raton's new beach and hopes to publish his results in a scientific journal. His hunch: About 6 inches of rainfall will leech salt out of the sand and the turtles will return.

The local turtle expert, who works out of the Gumbo Limbo Nature Center, suspects that briny sand warns turtles that the area is prone to water incursion during high tide. Turtle eggs exposed to water can drown or wash away. Because the beach is exposed to sea spray, the difference in salinity between beach sand and dredged sand is not great.

"The surprising thing to me is that a marine animal can detect that low level of salt," Rusenko said.

Salty sand may be just one of many readings a sea turtle takes of beach conditions. A 2000 study by the University of Florida's Center for Sea Turtle Research considered salinity as a factor but concluded that the slope is more important for sea turtles looking for a place to lay eggs. "Sea turtles may use multiple cues for next site selection," the paper concluded.

So why did the two turtles lay eggs on Boca Raton's salt-drenched beach? "Either by desperation, or that's where they want to go, or we're totally wrong," Rusenko said.