Rising Seas: Addressing Eroding Habitats on St. Catherines Island, Georgia

An aerial view of the coastline of St. Catherines Island, Georgia, where sea level rise is already impacting turtle nesting. The area shown here is experiencing shoreline retreat of greater than three meters per year. © Brian K. Meyer

An aerial view of the coastline of St. Catherines Island, Georgia, where sea level rise is already impacting turtle nesting. The area shown here is experiencing shoreline retreat of greater than three meters per year. © Brian K. Meyer

By BRIAN K. MEYER, R. KELLY VANCE, and GALE A. BISHOP

On St. Catherines Island, Georgia (U.S.A.), we—three geologists involved in sea turtle conservation—have been documenting the deterioration of sea turtle nesting habitat caused by sea-level rise since 1998. The geographic position of this barrier island and its limited sand supply have resulted in rapid erosion of back-beach nesting habitat at an average rate of 3 meters per year. As a result, adequate nesting habitat has declined from 25 percent to 12 percent of the total beach within a decade. Additional impacts from sea-level rise include fragmentation of three beaches into eight discrete beaches from 1990 to 2014, the formation of washover fans and wash-in fans of beach sand over back-beach marsh meadows and into the maritime forest, the formation of nearly continuous tree “boneyards” or scarps, and the exposure of relict marsh mud along nearly the entire beachfront.

The extreme shoreline changes on St. Catherines Island produce difficult conditions for nesting loggerhead sea turtles and challenge conservation efforts; however, these conditions also create an opportunity to develop, evaluate, and optimize conservation methods on this sentinel island. These erosional effects are expected to intensify as the rise of sea level accelerates, leading to further deterioration of loggerhead nesting habitat on St. Catherines Island.

As erosion continues and nesting habitat continues to diminish, we may see the turtles begin to shift their nesting patterns in response. So far, such adaptations have not been observed. We do know that the loggerhead population here and throughout the southeastern United States has already experienced significant decline as a result of human actions, which could impede the turtles’ ability to adapt. We have therefore decided to take a proactive approach to give the turtles their best chance at surviving and adapting to change.

A satellite image of St. Catherines Island with areas of erosion and accretion labeled in color, and arrows indicating locations of newly formed inlets. © SCISTP, 2014

A satellite image of St. Catherines Island with areas of erosion and accretion labeled in color, and arrows indicating locations of newly formed inlets. © SCISTP, 2014

Because Georgia has a large tidal range, many, if not most, turtles that nest during neap tides deposit clutches too low on the beach. Spring tides and storms can cause successive inundation of these “low nests,” which has been shown to reduce hatching success by as much as 77 percent. Our response has been to relocate a large portion of at-risk or “doomed” loggerhead nests.

Relocated nests are moved into “nurturies” on areas of the beach that are better suited to hatching clutches of eggs and are still being used by the loggerheads as natural nesting habitat. The original sites of relocated nests are staked, labeled, and monitored through the summer. We note whether they are washed out, as well as the number of times they are overwashed, and use this information to evaluate our relocation decisions. We have also used thermologger data to determine that our relocation of nests does not bias gender ratios, and we have actively managed predators to protect nests within the nurturies from predation.

We believe that such proactive measures are necessary until population levels reach the targeted management benchmark of 2,800 nests per year in Georgia set by the National Marine Fisheries Service and the U.S. Fish and Wildlife Service. The St. Catherines Island Sea Turtle Program will continue to monitor and evaluate the efficacy of our relocation efforts. We present the program as one possible model for sea turtle conservation by addressing nesting habitat threatened by the modern transgression.