The western terminus of Bald Head Island (BHI), in southeastern North Carolina, is located adjacent to the Bald Head Channel Range section of the Wilmington Harbor Navigation Channel. The channel has changed the morphology of the inshore habitat near BHI’s western beaches (Figure 1), and has accelerated erosion along BHI’s southward and westward facing beaches. As a means of protecting infrastructure, beach nourishment projects have been ongoing since 1991.

Beach nourishment projects have been found to affect a variety of sand characteristics such as grain size, moisture content, compaction, and more (Crain, et al. 1995; see Figure 2). Sand conditions have the potential to affect not only incubating eggs, but also nesting behavior of adult sea turtles. Rumbold, et al. (2001) noted a decrease in

nesting density one year post-nourishment with a concurrent increase in false crawl

activity. This raises concerns as to the effect of

BHI’s nourishment projects on the nesting and hatching population of sea

turtles that frequent BHI’s beaches.

Impacts of Beach Nourishment on Loggerhead (Caretta caretta) Nesting Trends on Bald Head Island, NC

Emily E. Hardin, Brooke K. Milligan, & G. Christopher ShankBald Head Island Conservancy, NC

Introduction

Discussion

Results

Methods

References

AcknowledgmentsThe authors would like to thank the many interns, nest monitors, volunteers, and staff of the Bald Head Island Conservancy for their continued hard work and dedication to collecting field data on our sea turtle population. The BHIC’s work is funded through private contributions and donations. Our sea turtle saturation tagging program would not be possible without the support of Dr. Matthew Godfrey and the North Carolina Wildlife Resources Commission. All research conducted under permit. A special thanks to the Village of Bald Head Island and Olsen Associates, Inc. for providing reports detailing the beach nourishment projects on Bald Head Island, NC, as well as to Kit Adcock for providing travel funds for BHIC staff to the 2017 ISTS.

• Brock, K.A., Reece, J.S., & Ehrhart, L.M. (2009). The effects of artificial beach nourishment on marine turtles: differences between loggerhead and green turtles. Restoration Ecology, 17(2), 297-307.

• Byrd, J.I. (2004). The effect of beach nourishment on loggerhead sea turtle (Caretta caretta) nesting in South Carolina (M.S. thesis). Retrieved from http://www.dnr.sc.gov/seaturtle/Literature/byrd-thesis.pdf

• Crain, D.A., Bolten, A.B, & Bjordnal, K.A. (1995). Effects of beach nourishment on sea turtles: review and research initiatives. Restoration Ecology 3(2): 95-104.

• Gallaher, A.A. (2009). The effects of beach nourishment on sea turtle nesting densities in Florida (Doctoral dissertation). Retrieved from http://nsgl.gso.uri.edu/flsgp/flsgpy09003.pdf

• Olsen Associates, Inc. (2016). “Bald Head Island, N.C. Beach Monitoring Program Report No. 14 (April 2015 – April 2016)”, Report prepared for Village of Bald Head Island. Olsen Associates, Inc. 2618 Herschel St., Jacksonville, FL 32204. 80 pp plus app. (June 2016).

• 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.

Figure 1. Morphology of Cape Fear River Entrance 1865 vs. 2005.

Figure 2. Sand 0 years post-nourishment (left) vs. 5 years

post-nourishment (right), Bald Head Island, NC.

Live Stragglers (Figure 7)• Significant differences were found in the median numbers of

live stragglers found in nest excavations each year post-nourishment (p=0.001)

• The first four years following nourishment showed averages ranging from 4 to 6 hatchlings, with a slight decline from 0 to 3 years

• Years 4 and 5 post-nourishment show almost double that number of stragglers, with averages of 10 and 8, respectively

Figure 5. The percentage of relocated nests did not have a significant relationship to year post-nourishment (R2=0.44, p=0.15).

Figure 4. The ratio of nests to false crawls did not show a significant relationship to years post-nourishment (0-2 years: R2=0.99, p=0.06; 3-5 years: R2=0.94,

p=0.15).

Figure 6. Average incubation times with standard error shown. Incubation durations

varied significantly among post-nourishment years (p<0.001).

Figure 7. Average numbers of live stragglers with standard error shown. Straggler

numbers varied significantly among post-nourishment years (p=0.001).

Success Rates (Figure 8) • Neither emergence success nor hatching success showed

significant differences among post-nourishment years (p= 0.53, 0.49, respectively)

• Yearly average success rates for all years except at 4 years post-nourishment were relatively constant during post-nourishment

(Note: emergence success is defined as the number of hatchlings that emerged from the nest naturally, while the hatching success is defined as the number of hatchlings that successfully escaped their eggshells.) Figure 8. Average hatching and emergence success rates with standard error shown.

Neither rate varied significantly among post-nourishment years (ES, p=0.53; HS, p=0.49).

Figure 9. Tracks leading to nest laid in nourished area 0

years post-nourishment

Data CollectionNesting and hatching data on BHI has been collected for >30 years by the Bald Head

Island Conservancy (BHIC) via all-night patrols and nest excavations. Using information provided by Olsen Associates, Inc. on the beach nourishment projects on BHI (Table 1), sea turtle data was separated into post-nourishment categories that ranged from 0 years (season directly following nourishment) up to 5 years (see Figure 3).

Beach Nourishment SourcesAll beach nourishment projects have sourced sand either directly from the

Wilmington Harbor Channel (as part of US Army Corps of Engineers channel maintenance operations) or from shoals and borrow sites within the Cape Fear River Entrance.

Data Analysis:Linear regressions were used to determine if there was a significant relationship

between the nest:false crawl ratios and years post-nourishment, as well as between the percentage of nests relocated and years post-nourishment.

Kruskal-Wallis one-way analysis of variance was chosen to test differences in incubation times, numbers of live stragglers, and emergence and hatching success. Kruskal-Wallis was used in substitution to ANOVA as the data was found to be non-parametric during Shapiro-Wilks Test for Normality.

P-values <0.05 were considered significant.

ObjectivesTo determine if beach nourishment projects on Bald Head Island, NC are affecting loggerhead (Caretta caretta) nesting and hatching trends by comparing the following factors for 6 years following nourishment projects:

• Numbers of live stragglers• Emergence success• Hatching success

• Ratio of nests to false crawls• Percentage of nests requiring relocation • Incubation durations

--- = 1991, 1996, 1997, 2001

--- = 2005--- = 2006--- = 2007--- = 2009--- = 2013--- = 2015

Figure 3. Beach nourishment projects

conducted on a section of BHI (image created with Google Earth & TerraMetrics).

Table 1. Overview of beach nourishment projects on BHI, NC (table taken from

Olsen Associates, Inc.)

Significant Findings• Nest:False Crawl Ratio – no significant relationship to years post-nourishment

• Percentage of Nests Relocated – no significant relationship to years

• Incubation Duration – significantly different among years post-nourishment

• Number of Live Stragglers – significantly different among years

• Emergence and Hatching Success – not significantly different among years

post-nourishment

Nest to False Crawl RatioPrevious studies have found that nesting activity has decreased the year following

nourishment, but has returned to pre-nourishment levels at least three years after the project (Brock, et al. 2009, Rumbold, et al. 2001, Byrd 2004).

Studies have also found that nourishment projects have different effects on differentbeaches and nesting populations(Gallaher 2009, Byrd 2004). While thisstudy did not include pre-nourishmentdata, the findings suggest that nestingactivity on BHI specifically did not vary inthe years following nourishment (Figure 9).

Percentage of Relocated Nests Beach nourishment can result in

escarpments (Crain, et al. 1995), which can prevent nesting turtles from advancing up the beach and often results in nests on BHI having to be relocated to avoid becoming exposed as the escarpment continues to erode. Escarpments are regularly present on BHI, and as such the percentage of nests needing relocation did not vary significantly for the six years following a nourishment project.

Incubation Durations & Live StragglersIncubation times and the numbers of live stragglers

varied across post-nourishment years. Previous studies have found differences in the sand quality of nourishedsand including differences in grain size, sand temperature, compaction, and more (Byrd 2004, Crain et al. 1995). These factors could influence dynamics inside the nests, including incubation durations.

Success RatesNeither emergence nor hatching success rates on BHI varied significantly among

post-nourishment years, despite other studies that have found negative impacts to nest success (Crain, et al. 1995). While the sand quality is visibly different between nourished and non-nourished areas of BHI, all sand for projects was sourced from inshore habitats or the navigation channel. This sand could be more compatible with natural beach sand as opposed to sand used in other nourishment projects, which could explain the differences in findings.

Figure 10. Live stragglers found in

nest excavation.

Ratio of Nests to False Crawls (Figure 4) • Highest ratio was seen at 3 years post-nourishment, with 1.70

false crawls for every 1 nest• Ratios appear to decrease slightly within first 3 years, dropping

from 1:1.46 to 1:1.15 • Linear regression of 0 – 2 years post-nourishment proved the

relationship not significant (R2= 0.99, p=0.06)• Similarly, there was no significant relationship between 3 to 5

years (R2= 0.94, p= 0.15)

Percentage of Nests Relocated (Figure 5) • 62% of nests laid in nourished areas 0 years post-nourishment

required relocation• Percentage dropped to 37% by 1 year post-nourishment, but

increased again slightly at 2 years• Overall, there was no significant relationship between years

post-nourishment and the percentage of nests relocated (R2= 0.44, p= 0.15)

• Season following a post-nourishment project retained the highest percentage of nests requiring relocation

Incubation Durations (Figure 6) • Kruskal-Wallis tests indicate that there was a significant

difference between the incubation durations of nests 0 to 5 years post-nourishment (p<0.001)

• Similar to nest:false crawl ratios, the average incubation times seem to decrease during the first three years following a nourishment project, but increase again at 3 years post-nourishment

• The year following a nourishment project had the highest average incubation rate of 58 days