the slope of our beaches and how it affects sea turtle nestgin
TRANSCRIPT
Introduction – Groins } Installed in 1996 } Currently 15 groins } Tubes made of geotextile materials and filled with sand } Used to combat erosion
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.