Storm event, turtle nest losses, no red flags yet
BY JACK SHORT – Two weeks of onshore wind and pounding waves have taken their toll on sea turtle nests here on the island, but authorities do not seem alarmed, saying that changes to the beach profile and the resulting sea turtle nest losses are expected.
A representative of the Boca Grande Sea Turtle Association said in an email to the Beacon that she estimates the losses due to flooding, or inundation, and loss of sand to be more than 25 percent of the nests they monitor. The BGSTA and the Gasparilla Island State Park together monitor all sea turtle activity on Gasparilla Island. State park representatives said they had 15 nests at the onset of the storms, six of which, including one Green Turtle (a rare species) nest, were lost because of sand washing away or surge from the storm.
Much of the sand lost was placed during a beach renourishment, completed in 2013. Those renourishments are up for renewal every seven years, according to Steve Boutelle, coastal projects manager for Lee County.
“There’s no reason for heightened concern,” Boutelle said of the sand’s movement. “The beach reacted as expected.”
He explained that the active beach profile includes submerged sand as well, and surmised that since storm energy came almost directly onshore (with little sideshore angle), most of the sand lost will likely end up on sandbars just offshore, and remain a part of that profile.
Moreover, turtle nest losses are expected as well.
“This happens every year,” said Anne Meylan, senior research scientist at the Florida Fish and Wildlife Research Institute. “It’s unfortunate. But sea turtles lay a lot of eggs. They’re evolutionarily designed to take some losses.”
Based on three years’ data, provided by the FWC, collected from what it called a representative sample of nests across the state, average losses due to inundation and storm activity for the last three years were 8.4 percent for loggerhead turtles, 10.8 percent for green turtles, and 5.0 percent for leatherback turtles.
Losses on Gasparilla Island may be higher than other Florida beaches, if nests were built on sand that was placed but expected to erode. The “sacrificial fill,” as it was called in an email from the United States Coast Guard, which oversees beach renourishment projects, “is expected to erode,” and erosion is “built into the project design,” according to the same email.
Robin Trindell, biological administrator for the FWC, said that in some cases contractors that performed a renourishment can be obligated to smooth over jagged events or extreme escarpments in the beach profile, but this is not one of those cases.
“We would take a wait-and-see approach,” Trindell said. “… it’s assumed through a process called equilibration that the waves will re-sort some of that (displaced) sand.”
In spite of that, Trindell said that an escarpment of more than 18 inches that extends for 100 feet or more along the shore can raise red flags.
“(Nesting sea turtles) respond to cues like changes in elevation,” she said.
But just how to shape a beach so that turtle nests are built out of harm’s way can be more tricky than it seems. Building too far upland can put them at risk of predation, just as building too close to the water can lead to losses from inundation, according to Trindell.
The FWC is conducting studies to determine just how beach profiles should be designed during renourishments, she said, adding that failing to renourish any particular beach is also problematic, since nesting on a narrow, eroded strand also leads to losses.
In any case, she echoed other experts’ response that losses are a part of the sea turtles’ nesting cycle. Just how much this storm event will affect sea turtle populations, as well as the beaches themselves, remains to be seen.
According to Boutelle, the USACE just completed the first of several periodic assessments of post-renourishment changes to the beach profile.
According to a USCG representative, that survey was completed “recently” and the results are expected in September.
However, that assessment will not include this storm event, as it was completed before it occurred, according to Boutelle. Another assessment is scheduled to be performed on the two-year anniversary of the renourishment.
