- April 18, 2024
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The slope of a dune affects how likely sea turtles are to nest there, and how susceptible the nests are to washouts. (Photo by Brian McMillan)
The slope of a dune affects how likely sea turtles are to nest there, and how susceptible the nests are to washouts. (Photo by Brian McMillan)
Sea turtle hatchlings make their way to the ocean. (File photo)
Seawalls, such as the one the Florida Department of Transportation has proposed to protect 1.3 miles of State Road A1A in Flagler Beach after Hurricane Matthew, contribute to erosion that degrades sea turtle nesting habitat — so much so that turtles that come to shore to nest in seawall areas tend to return to sea without laying their eggs, according to U.S. Fish and Wildlife experts.
FDOT needs the Fish and Wildlife Service’s approval to make certain modifications on the nesting habitat of endangered turtles. The Fish and Wildlife Service granted that approval in 2009, but with numerous caveats and explanations of how a seawall tends to harm turtle habitat. That 2009 approval was for a shorter stretch of beach than the seawall FDOT proposed after Hurricane Matthew, U.S. Fish and Wildlife Service Southeast Sea Turtle Coordinator Ann Marie Lauritsen said, so FDOT would have to return to the Fish and Wildlife Service again for approval of the longer proposed seawall.
“Seawalls are one of the greatest threats to turtles on the nesting beach, because of the alterations that occur and the permanent loss of habitat,” Lauritsen said. “It does cause a change of the beach profile, which also affects turtles because turtles need a slope to nest.”
The Fish and Wildlife Service has recently been seeing more evidence of “false crawls” — where a sea turtle crawls onto the beach, and then leaves without nesting — in St. Johns County, which has added seawalls over the past two years, Lauritsen said.
The 2009 Biological Opinion paper issued by the Fish and Wildlife Service concerning an FDOT proposal to add seawalls along 3,000 feet Flagler Beach assented to the seawall proposal not because the walls aren’t bad for turtles, but rather because the erosion of Flagler Beach’s beach had been so severe already, and had so degraded the nesting habitat, that a seawall, in the Service’s analysis, wouldn’t have made a significant difference in that area.
Lauritsen said the agency, looking at a new, longer seawall proposal, might recommend that FDOT explore possibilities like moving portions of S.R. A1A inward, or adding a seawall in only portions of the proposed 1.3-mile stretch. If it approved a seawall, the agency would likely recommend that it be placed behind a vegetated dune, and positioned as close to the roadway as possible, she said.
Citing a 1998 study, the 2009 Biological Opinion states: “Fewer turtles emerged onto beaches in front of seawalls than onto adjacent, non-walled beaches, and of those that did emerge in front of seawalls, more returned to the water without nesting.”
But, as things were, stormwater runoff in Flagler Beach dissipated in ways that sped erosion, washing out areas of the dune and sometimes swamping nesting areas or leaving them under a large deposit of sand, according to the Biological Opinion.
“As the water stages up, the force of the water washes out the berm and flows directly onto the beach,” the paper states. “Depending on the severity of the rain event, the stormwater erodes the dune crest and dune face, often transporting large amounts of sand onto the beach. The delta-like deposition can result in additional material on top of turtle nests, altering the depth of the eggs or emerging hatchlings. As the erosion continues, large trenches are formed that can wash out nests from the large volumes of water coming off the impervious surface.”
Though seawalls and other coastal armoring structures do tend to change the beach profile, in Flagler Beach, the paper states, “The loss in habitat quality is expected to continue if the erosion continues,” and the number of turtles killed by the then-proposed wall “is not likely to result in jeopardy to the species or destruction or adverse modification of critical habitat.”
The 2009 Biological Opinion recommends that local, state and federal agencies “develop and implement coastal dune restoration projects to stabilize and enhance sea turtle nesting habitat.”
With renourishment, Lauritsen said, “There is an impact, and we have many terms and conditions to follow. … But we can minimize that impact, and turtles can continue to nest in that area.”
If the Fish and Wildlife Service were to again give its approval for a seawall, Lauritsen said, there would be conditions.
The 2009 Biological Opinion laid out a number of requirements for how FDOT would be expected to proceed if it were to create a seawall in Flagler Beach, setting guidelines for non-emergency work to keep it out of the April 15 to Nov. 30 nesting season, and requiring the construction of a vegetated dune in front of the seawall.
That dune would have to be sloped with a 1.5:1 slope followed by a gradual slope of 4:1, according to the paper.
If a seawall is constructed, according to the 2009 paper, the Fish and Wildlife Service will have to augment its sea turtle monitoring program in that area for five years after construction.
