The Slope of Our Beaches and How it Affects Sea Turtle Nesting

Emily Hardin Jaymie Reneker

Introduction – Groins }  Installed in 1996 }  Currently 15 groins }  Tubes made of geotextile materials and filled with sand }  Used to combat erosion

Longshore Drift Longshore Drift

Is this also changing the slope of the beach?

Introduction – Beach Nourishment }  Section of South Beach is re-nourished }  650,000 m3 of sand initially dredged and added }  Re-nourished every few years }  Thought to have negative effects on sea turtle nesting

Village of Bald Head Island

Slurry Systems Marine Pty Ltd

Introduction – Beach Nourishment and Sea Turtles

}  Increases the amount of nest-able beach }  Affects:

}  Sand composition and temperature }  Slope

}  Loggerheads nest more frequently in areas with less shells (Garmestani, et al. 2000)

}  Number of nests has been found to decrease after nourishment (Rumbold, et al. 2001)

Introduction - Slope }  Slope is the most influential factor in nest site selection

(Wood & Bjorndal 2000) }  Slope preference can vary among species (Cuevas, et al. 2010)

}  Hawksbill prefer less steep beaches }  Greens prefer more steep beaches

}  Loggerheads prefer flatter slopes (Garmestani, et al. 2000) }  Different populations may have different preferences

(Cuevas, 2010)

Gnaraloo Turtle Conservation Program

Objectives }  Measure slope in four areas of Bald Head Island:

}  South Beach – groin field and re-nourishment }  South Beach – natural }  East Beach – developed }  East Beach – undeveloped

Objectives }  Measure slope in four areas of Bald Head Island }  Measure the slope of sea turtle nests }  Determine if:

}  Slope varies over the course of the summer }  Slope varies from location to location }  Sea turtles have a preferred slope }  Which beach is preferred by turtles

Methods }  Used slope profile poles

}  Started at vegetation line, measured to water line }  Measurements taken at low tide (± 2 hrs) }  Measurements taken every 2 weeks

Methods }  Measure the slope of nests

}  Caged nests: began halfway on either side of cage

}  Relocated nests: from center of body pit at original site

}  ANOVA test to determine if measurements differed

significantly }  p-value of 0.05

Results }  Did the slope change over time?

}  All areas except the natural section of South Beach changed significantly }  Groins, p=4.5x10-8 }  East Developed, p=3.4x10-5 }  East Undeveloped, p=0.04 }  South Natural, p=0.30

}  Second measurements seemed to be the greatest

Results }  Does the slope vary from location to location?

}  No significant difference in the average slope of each location (p=0.77)

}  Groins have steepest slope

Results }  Do our sea turtles have a preferred slope?

}  No, the slopes of nests are not statistically similar

} 

Results }  Which beaches do our turtles prefer?

}  Average slope of nests = -2.38 }  Most similar to South Natural and East Developed

Conclusions & Implications }  Slope changes over time }  Bald Head Island has a pretty uniform slope on all its

beaches }  Groins and beach re-nourishment are NOT affecting slope

}  Our population does not have a preferred slope }  Since the slope changes frequently, this allows them to be able

to nest throughout the summer

}  Average slope of ascents is similar to South Natural and East Developed beach slope }  Majority of our nests }  Factors other than slope may be at play

Further Directions }  Year-long study to observe slope changes over multiple

seasons }  Measure the slope of false crawls }  Take measurements more frequently }  Look back at previous data and continue study over time

Amelia Island Sea Turtle Watch, Inc.

References }  Cuevas, E., Liceaga-Correa, M.A., Marino-Tapia, I. (2010). Influence of Beach

Slope and Width on Hawksbill (Eretmochelys imbricata) and Green Turtle (Chelonia mydas) Nesting Activity in El Cuyo, Yucatan, Mexico. Chelonian Conservation and Biology, 9(2), 262-267.

}  Denison, P.S. (1998). Beach Nourishment/groin field construction project: Bald Head Island, North Carolina. Shore and Beach, 66(1), 2-9.

}  Garmestani, A.S., Percival, H.F., Portier, K.M., Rice, K.G. (2000). Nest-Site Selection by the Loggerhead Sea Turtle in Florida’s Ten Thousand Islands. Journal of Herpetology, 34(4), 504-510.

}  Rumbold, D.G., Davis, P.W., Perretta, C. (2001). Estimating the Effect of Beach Nourishment on Caretta caretta (Loggerhead Sea Turtle) Nesting. Restoration Ecology, 9(3), 304-310.

}  Wood, D.W., Bjorndal, K.A. (2000). Relation of Temperature, Moisture, Salinity, and Slope to Nest Site Selection in Loggerhead Sea Turtles. Copeia, 2000(1), 119-128.

Acknowledgements }  Thank you to everyone who helped me measure!

}  Brandt Quirk-Royal (+ modeling) }  Matt Salinski }  Connor Hinton (+ modeling) }  Amy Eldredge }  Abbie Dwire }  Savannah Currens }  Colleen MacGilvray }  Sara Thompson

}  Thank you to the one and only: }  Jaymie Reneker