Statewide Atlas of Sea Turtle Nesting Occurrence and Density
The Fish and Wildlife Research Institute (FWRI) coordinates the Statewide Nesting Beach Survey program (SNBS) to document the total distribution, seasonality and abundance of nesting by sea turtles in Florida. The SNBS program was initiated in 1979 under a cooperative agreement between the FWC’s predecessor agency and the U.S. Fish and Wildlife Service. Three species of sea turtles – loggerhead (Caretta caretta), green turtle (Chelonia mydas) and leatherback (Dermochelys coriacea) – regularly nest on Florida beaches. Two other species – Kemp’s ridley (Lepidochelys kempii) and hawksbill (Eretmochelys imbricata) – also nest in Florida, but in very small numbers. All of these sea turtle species are listed as either threatened or endangered under the Endangered Species Act, and monitoring nesting activity is critical to understanding the biology and ecology of these imperiled species. Managers use survey results to evaluate and minimize impacts to sea turtles and their nests from human activities such as coastal construction, beach renourishment and recreation. They also use survey results to identify important areas for enhanced protection or land acquisition.
Using Statewide Nesting Beach Survey data collected during the last five years, FWRI researchers prepared a statewide atlas of nesting occurrence and density for loggerheads, green turtles and leatherbacks. They represented the distribution of Kemp’s ridley and hawksbill nesting as occurrence (presence or absence). Nest density and nest occurrence information was attributed to each beach surveyed as part of the SNBS program. Prior to the assignment of density ranks, researchers excluded survey beaches on which these three species were not observed to have nested during the five-year time period. These beaches were placed in the “not present” category within the density classification field.
Researchers used quartile ranks – dividing density into four parts, each containing a quarter of the density values – to develop density classifications of “low,” “medium” and “high.” Researchers defined high-density beaches as those having the top 25 percent of density values; low-density beaches as the lowest 25 percent; and beaches with densities between these two categories as medium-density beaches. For loggerhead turtles and green turtles, researchers ranked nesting activity within each genetic subunit described by Shamblin et al. (2011, 2012, 2015); ranks for leatherbacks were done on a statewide basis. Hawksbill turtles and Kemp’s ridleys are noted as present or absent on individual beaches during the specified five-year time period. It is important to note that nesting beach surveys may have varied start and stop dates, frequency, duration and beach length between years for a particular beach, as well as between different beaches.
Citations
Shamblin, B. M., Dodd, M. G., Bagley, D. A., Ehrhart, L. M., Tucker, A. D., Johnson, C., Carthy, R. R., Scarpino, R. A., McMichael, E., Addison, D. S., Williams, K. L., Frick, M. G., Ouellette S., Meylan, A. B., Godfrey, M. H., Murphy, S. R., and Nairn, C. J. 2011. Genetic structure of the southeastern United States loggerhead turtle nesting aggregation: evidence of additional structure within the peninsular Florida recovery unit, Marine Biology 158:571-587).
Shamblin, B. M., Bolten, A. B., Bjorndal, K. A., Dutton, P. H., Nielsen, J. T., Abreu-Grobois, F. A., Reich, K. J., Witherington, B. E., Bagley, D. A., Ehrhart, L. M., Tucker, A. D., Addison, D. S., Arenas, A., Johnson, C. Carthy, R. R., Lamont, M. M., Dodd, M. G., Gaines, M. S., LaCasella, E., and Nairn, C. J. 2012. Expanded mitochondrial control region sequences increase resolution of stock structure among North Atlantic loggerhead turtle rookeries. Marine Ecology Progress Series 469:145-160.
Shamblin, B.M., Bagley, D.A., Ehrhart, L.M. et al. 2015. Genetic structure of Florida green turtle rookeries as indicated by mitochondrial DNA control region sequences. Conservation Genetics 16: 673. doi:10.1007/s10592-014-0692-y