In 1978, the loggerhead sea turtle (Caretta caretta) was listed as Threatened under the Endangered Species Act of 1973 as a result of widespread population declines (43 FR 32800; Federal Register 1978). The Recovery Plan for the Northwest Atlantic Population of the Loggerhead Sea Turtle (Caretta caretta; National Marine Fisheries Service–US Fish and Wildlife Service [NMFS-USFWS] 2008) lists nest monitoring and control of nest predation as objectives for population recovery. Many sea turtle nesting beaches have initiated beach monitoring programs and nest protection measures as a component of population recovery efforts (Ehrenfeld 1995). When combined with in-water protection of juvenile and adult sea turtles, active monitoring and nest protection can facilitate population growth (Frazer 1992; Crowder et al. 1994; Grand and Beissinger 1997; Dutton et al. 2005).

Hatching success (number of hatchlings leaving the eggs; Miller et al. 2003) and emergence success (number of hatchlings reaching the beach surface; Miller et al. 2003) can be affected by multiple factors, including elevation, slope, predation, moisture, and temperature (Wood and Bjorndal 2000). Nesting females are thought to use sensory clues to select nesting sites that have the highest probability of nest survival (Bjorndal and Bolten 1992). Nests laid close to the sea are more susceptible to tidal inundation and have increased potential for erosional damage, whereas nests located farther inland risk higher rates of nest predation (Fowler 1979; Marchand and Litvaitis 2004).

Relocation of nests into hatcheries or corrals is a method commonly used by beach managers to protect nests from depredation (Marcovaldi et al. 2007). Nest relocation is also used as a conservation tool to reduce tidal inundation risk (Eckert and Eckert 1990; Dutton et al. 2005). Previous studies on the effects of nest relocation report conflicting results, and most studies have used hatcheries or corrals rather than natural sites for relocation. On Jekyll Island, Georgia, Wyneken et al. (1988) found lower hatching success in in situ nests than in nests relocated to natural sites. In their study, however, nests selected for relocation were only those considered to be at risk of tidal inundation, and data were analyzed under the assumption that each relocated nest would have failed (hatching success = 0) if left in situ. Additionally, the sample of nests relocated to natural sites was limited to 5 nests. Of the 20 remaining in situ nests, Wyneken et al. (1988) reported an 87% hatching success rate. On Blackbeard Island, Georgia, Tuttle and Rostal (2010) also found lower hatching success in in situ nests than in nests relocated above the spring high tide line (SHTL). Nests above SHTL had higher hatching success than those below SHTL. All nests in this study were excavated and had temperature data-loggers installed (there was not a control for human manipulation of the nest) and each nest was covered with a metal screen. In an analysis of results compiled from multiple nesting beach studies, Grand and Beissinger (1997) found hatching success of nondepredated in situ nests was significantly higher than those relocated to corrals. Grand and Beissinger (1997) concluded that relocation to protected areas would likely increase hatching success only on beaches experiencing poaching and predation, and otherwise recommended in situ nest protection to avoid movement-induced mortality as described by Limpus et al. (1979). Other reported adverse effects of nest relocation include altered sex ratios (Mrosovsky and Yntema 1980) and compromised egg hatchability (Parmenter 1980). Relocation also has been shown to affect hatchling emergence patterns (Adam et al. 2007) and rates (Glen et al. 2005) by altering the original incubation environment.

Wire or plastic cages and screens are often used to protect nests from predators (Ratnaswamy et al. 1997; Mroziak et al. 2000; Irwin et al. 2004; Antworth et al. 2006). Screening significantly improves hatching success by reducing nest depredation (Ratnaswamy et al. 1997; Antworth et al. 2006); however, potential effects of installation and presence of screens have not been investigated. Wire screens have been shown to alter local magnetic fields, possibly affecting hatchlings’ ability to navigate (Irwin et al. 2004). This potential negative effect has prompted some sea turtle nesting beaches in Georgia to use plastic protective screens (M.G. Dodd, pers. obs.).

Although several studies have reported success rates of nests reared in hatcheries, few studies to date have investigated hatching or emergence success in relocated, hand-excavated nests in natural dunes. In this study, we measured the effects of nest relocation and nest screening on loggerhead hatching and emergence success. Sapelo Island, with limited human access and a low incidence of sea turtle nest depredation relative to other Georgia barrier islands, was selected as an optimal location for investigating the effects of both nest relocation and nest screening. Based on preliminary data and observations from preceding years, we hypothesized that hatching and emergence success on Sapelo would not be affected by presence of plastic screens and would not differ between in situ and relocated nests.

METHODS

Study Area

We conducted our study on Sapelo Island, a barrier island located in McIntosh County, Georgia, United States. The ocean shoreline consists of 2 beaches, Cabretta (2.5 km) and Nannygoat (6.8 km), separated by a small tidal creek. The beaches are low energy, widely sloping, and composed of fine-grain silica sand. A small wooden pavilion on Nannygoat is the only permanent structure on the beaches. Anthropogenic activity is low because the island has fewer than 100 permanent residents and limited visitor access.

Beach Monitoring

We patrolled the entire length of both beaches daily at dawn. We used 4-wheel-drive vehicles for surveys and restricted driving below the previous night’s tide line to avoid disturbance of beach-nesting birds and turtle nests and to ensure that all sea turtle emergences were detected. We conducted daily patrols for the duration of Georgia’s sea turtle nesting season (15 May–1 October) in 2002–2007.

When evidence of a loggerhead nest was detected, we applied 1 of 5 treatments: 1) locate egg chamber, nest left in situ; 2) locate egg chamber, nest left in situ with screen placement; 3) locate egg chamber, relocate nest without screen placement; 4) locate egg chamber, relocate eggs with screen placement; and 5) a control (do not locate egg chamber, do not relocate or place screen). Treatments were applied using a stratified random design by dividing nests into 5 sequential subgroups through the nesting season and applying treatments randomly within each subgroup. We located the egg chamber by probing gently in the body pit with a blunt wooden dowel rod. Relocated clutches were moved to the apex of the nearest primary dune following the standard procedure used on Georgia beaches. Permit holders are required to relocate nests as close to the original nest site as possible to maintain a spatial distribution comparable to an unmanipulated beach.

Treatment Protocols, Treatment 1

We removed sand by hand from the area above the egg chamber until egg location was visually confirmed. We replaced sand removed during the nest search and smoothed the nest area by hand.

Treatment Protocols, Treatment 2

We confirmed egg location and sand was replaced over eggs as in Treatment 1. We placed a flat, white, plastic 4.1 × 4.1-cm mesh screen on top of the sand, with the center of the screen aligned above the egg chamber location. Screens were approximately 1.22 × 1.22 m and were secured with a bent steel rod at each corner.

Treatment Protocols, Treatment 3

We located the nest chamber and carefully removed and placed the eggs in a 5-gallon plastic bucket. We maintained the vertical orientation of eggs as accurately as possible. When all eggs were excavated from the in situ chamber, we constructed a new egg chamber by hand or with a small shovel on a nearby, ocean-facing primary dune. We attempted to reproduce the dimensions of the original egg chamber as closely as possible, including nest depth and shape. We replaced the sand and smoothed over the nesting site by hand. All nest relocations were performed within 12 hrs of deposition.

Treatment Protocols, Treatment 4

We conducted nest relocation as in Treatment 3. After sand was smoothed over, we installed a plastic mesh screen as in Treatment 2.

Treatment Protocols, Treatment 5

We identified the emergence as a nest based on field signs, including the presence of a body pit with disturbed sand, evidence of thrown sand, and uprooted vegetation. We estimated the location of the egg chamber by the boundaries of the body pit and direction of thrown sand.

Nest Monitoring

We marked all nests with a wooden stake placed approximately 1 m inland of the egg chamber location. We placed a mark on the stake at the elevation of the top of the nest at deposition. We monitored nests daily for the duration of incubation (55–70 d). We assessed predator activity by daily track counts, estimated within a 2-m radius of each egg chamber location. We recorded attempted, partial, and complete nest depredations.

We excavated nests on the fifth day following the first sign of hatchling emergence. We excavated nests without sign of hatching at 70 d after deposition. We recorded total hatched eggs, unhatched eggs, live hatchlings, and dead hatchlings. For in situ nests (in which the initial number of eggs was unknown), we estimated the total number of eggs by counting eggshell fragments ≥ 50% intact as 1 egg. Although the exact number of eggs in relocated nests was recorded at the time of relocation, we used this ≥ 50% estimation method to calculate total eggs in our analysis in an effort to maintain consistent error rates. After all nests were hatched, land survey crews (Wilder & Stone Land Surveyors, Inc., Rincon, GA) measured height (m) above mean low water of each nest. The land survey crew used the mark on the stake corresponding to the top of the nest at deposition to determine elevation. We measured the vertical distance from the mark on the stake to the level of sand over the nest center to estimate changes in sand level over the course of incubation.

Data Analysis

We included 5 yrs of nesting data (2002, 2003, and 2005–2007; n = 380) in our analysis. Data from 2004 were excluded after the majority of nest markers were lost to midseason tropical storms, making it impossible to evaluate hatching and emergence success and elevation. We used arcsin transformation to transform hatching and emergence success values from percentages to degrees for analysis. Calculations used were as follows:

We used an analysis of covariance (ANCOVA) in a randomized complete block design to examine treatment effects on hatching success and emergence success (α = 0.05). We included nesting year as a block to account for annual variation in hatching and emergence success. We included nest elevation measurements as a covariate. To test the assumption of heterogeneous slopes for ANCOVA, we included the interaction between treatment and elevation in the model. Because our investigation of nest elevation was confounded by the intentional placement of relocated nests at higher elevations, we used a simple linear regression analysis to further examine the relationship between in situ nest elevation and hatching success with relocated nests removed from the data set. SAS Statistical Analysis Software (Version 9.1) was used to perform all analyses.

RESULTS

Of 380 total treated nests, 212 were left in situ (Treatments 1, 2, 5) and 168 nests were relocated (Treatments 3, 4). Mean success rates across all treatments ranged from 70% to 80% hatching success and 67% to 78% emergence success (Table 1; Appendix).

Table 1. Mean loggerhead turtle hatching and emergence success rates (%), standard deviation (SD), and range of 5 treatments used to examine the effect of nest relocation and screening on Sapelo Island, Georgia, 2002–2007. Treatments were 1) locate egg chamber in situ, 2) locate egg chamber in situ with screen placement, 3) relocate eggs without screen placement, 4) relocate eggs with screen placement, and 5) a control (do not locate egg chamber, relocate, or place screen).

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Complete nest failure (hatching success = 0) occurred in 44 (20.7%) in situ nests and 13 (7.7%) relocated nests during the course of the study. However, the remaining in situ nests (those that did not completely fail) had a higher hatching and emergence success than the relocated nests. Of the 57 failed nests, 28 in situ nests and 2 relocated nests were washed over 1 or more times. Mean hatching and emergence success was lower in nests that were washed over > 3 times (Table 2). Of nests that were not inundated, in situ nests had higher mean hatching and emergence success than relocated nests. Raccoons (Procyon lotor) completely depredated 9 nests (4 in 2002 and 5 in 2003), and partially depredated 9 nests (3 in 2002 and 6 in 2003; Appendix). Of the nests completely depredated by raccoons, 5 were in situ without a protective screen (Treatments 1 and 5) and 4 were relocated without a screen (Treatment 3). No nests with plastic screening were depredated. Although raccoon depredations only occurred in 2002 and 2003, tracks were recorded within 2 m of the nest at approximately 35% of all nests across all treatments for the duration of the study. The observation of raccoon tracks was consistent among years, ranging from 32% to 38%. Typically, a single track was noted over a 2–3-d period. We assume ghost crab (Ocypode quadrata) depredations also occurred throughout the study; however, crabs appeared to destroy or remove few eggs per nest (< 5 eggs). Because individual egg losses were difficult to monitor and attribute to ghost crabs with certainty, these losses were not considered in our assessment of nest depredation.

Table 2. Mean loggerhead turtle hatching and emergence success rates (%) in nests that were inundated by seawater and nests that were not inundated on Sapelo Island, Georgia, 2002–2007.

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Nest elevation of in situ nests ranged from 2.66 to 5.59 m, whereas elevation of relocated clutches ranged from 3.04 to 5.22 m (Appendix). We did not find a treatment effect on hatching success (p = 0.09) or emergence success (p = 0.26) when adjusted for elevation. Nesting year approached significance when accounting for annual variation in hatching success (p = 0.07), whereas emergence success rates showed a significant year effect (p = 0.02). Elevation was a significant covariate in each ANCOVA (p < 0.0001); however, regression analysis indicated that elevation explained only a small amount of variation in in situ nest-hatching success rates (r² = 0.08; Fig. 1). Neither hatching success (p = 0.06) nor emergence success (p = 0.11) differed when ANCOVA was performed on only in situ nests (Treatments 1, 2, and 5; n = 213). Interaction between treatment and elevation was not significant for hatching success (p = 0.08) or emergence success (p = 0.30), suggesting that the slopes of the regressions within treatments were not significantly different.

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DISCUSSION

We did not find a difference in hatching and emergence success rates between management treatments applied to loggerhead nests on Sapelo Island, which supports a similar result found at a loggerhead nesting beach in South Carolina (Stancyk et al. 1980). In situ nests had a higher rate of total failure in our study; however, of those that did not fail, the hatching and emergence success tended to be higher than those of relocated nests. In contrast, Tuttle and Rostal (2010) found lower hatching success in in situ nests than in nests relocated above SHTL on neighboring Blackbeard Island, Georgia. However, the original nest locations relative to SHTL are not described and may be an important factor given the relatively small sample size (35 in situ nests and 34 relocated nests). Regardless, these conflicting results illustrate the importance of considering beach variability when developing state-wide beach management protocols.

In the absence of nest predation, hatching success of in situ nests is greater than that of relocated nests across a range of international loggerhead nesting beaches (Grand and Beissinger 1997). In the US Virgin Islands, relocation significantly reduced hatching success in leatherback nests on a beach with minimal predator activity (Eckert and Eckert 1990). To avoid movement-induced mortality, Grand and Beissinger (1997) support protection of in situ nests rather than nest relocation on beaches with minimal nest predation.

Installation and presence of plastic screens to protect nests from predators did not affect hatching or emergence success in our study. Wire screening has been shown to reduce nest depredation, thereby increasing hatching success rates on beaches with high levels of predator activity (Ratnaswamy et al. 1997; Baskale and Kaska 2005; Antworth et al. 2006); however, we are unaware of studies to date that have investigated the effect of screens on nest success rates, nor have plastic screens been evaluated. Despite the low predation risk on Sapelo Island, our results suggest that plastic screens could continue to be used as a precautionary measure with no effect on hatching or emergence success. Further investigation of the effectiveness of plastic screens against heavy nest predation is warranted, because replacement of wire screens with plastic mesh screens could avoid potential disruption of magnetic fields around the egg chamber (Irwin et al. 2004).

Although elevation has been shown to influence nest success of hawksbill turtles (Eretmochelys imbricata; Horrocks and Scott 1991), elevation explained little variation in our estimates of hatching success. Contrary to expectations, in situ nests in our study had a higher maximum elevation than relocated nests because turtles occasionally nested in secondary dunes, which were generally at higher elevations than the primary dunes used for relocation sites. Thus, considering elevation for use in beach management protocols is a challenge. Although a primary dune may provide a well-elevated nest site, its proximity to the incoming tide is an important consideration. Anecdotal observations suggest distance to tide line influences nest fate at Sapelo Island (M.G. Dodd, pers. obs.). Elevation could potentially be used as an index of nest fate when combined with measurements of nest distance-to-tide. Such measurements would depict the location of each nest more accurately, providing a more reliable indicator of nest fate.

The observed differences in block (year) effect could be caused by environmental and anthropogenic factors that vary annually. Rain and vegetation growth can create barriers to emergence, such as hardened sand and heavy root growth above the egg chamber (Kraemer and Bell 1980). Such barriers could be more likely to affect emergence success than egg hatchability. The incidence of tidal inundation and depredation of nests also varies annually. Also, the personnel conducting nest surveys and relocations change every year or two (M.G. Dodd, pers. obs.). Although nest treatment protocols are standardized, relocation techniques are subject to individual variation in digging methods and nest site selection, which could contribute to annual differences in hatching or emergence success.

Apart from confirmed depredation events and tidal inundation of clutches, the causes of many of our in situ and relocated nest losses are uncertain. Although a number of our failed relocated and in situ nests were washed over more than once, the extent of inundation in these nests is not known. Tidal wash-overs increase embryonic mortality and decrease hatching success (Whitmore and Dutton 1985; McGehee 1990; Peters et al. 1994). However, loggerhead nests can withstand multiple tidal wash-overs, dependent on the extent of inundation of the egg chamber (Foley et al. 2006). Of the nests that were not inundated, our relocated-nest success rates were lower than success rates of in situ nests. In the absence of other potential egg mortality factors, lower nest success of relocated nests suggests movement-induced mortality or another, unknown factor related to the act of relocation is affecting nest success. Other environmental factors may have contributed to decreased success rates in nests that were not depredated or washed over in our study. In eggs that were unhatched, we were unable to consistently, definitively determine the cause. Individual eggs were sometimes ruptured by ghost crabs, roots, or ants, which may have reduced overall hatching success by introducing fungus or bacteria (Fowler 1979; Whitmore and Dutton 1985). Microbial pathogens also significantly affect hatching success (Wyneken et al. 1988). Invasion of plant roots may also create sand compaction above and around the egg chamber, hindering hatchling emergence (Lohmann et al. 1996). The impact of root growth on emergence success may be more prevalent in nests located in the dunes, where vegetation is more abundant. Sand compression, which may occur when sand accretes above the egg chamber, negatively impacts emergence success (Peters et al. 1994) and may have affected some of the nests in our sample.

CONCLUSIONS

Based on high mean success rates across treatments, paired with low levels of human disturbance and predator activity, current hatching and emergence success rates on Sapelo Island could be maintained through a conservative nest-relocation strategy. Although some low-lying nests are inevitably washed-over, similar pressures on hatching and emergence success appear to be exerted on both relocated and in situ nests at various elevations. Management techniques involving relocation of all or a majority of nests may not be effective in increasing hatching and emergence success. Relocation should be used discriminately and applied only in circumstances where complete failure due to tidal inundation is expected for an in situ nest. The absence of a treatment effect in our study could be interpreted to advocate nest relocation; however, several potential negative effects of nest relocation have been reported, such as increased embryo and hatchling mortality (Limpus et al. 1979; Stancyk et al. 1980; Blanck and Sawyer 1981; Eckert and Eckert 1990), sex ratio alteration (Mrosovsky and Yntema 1980), gene pool alteration (Mrosovsky 2006), increased hatchling disorientation (Godfrey and Barreto 1995; Kamel and Mrosovsky 2005), increased risk of vegetation root invasion of the egg chamber (Whitmore and Dutton 1985), and increased exposure time to predators upon emergence (Mrosovsky 2006). Such risks were not quantified in this study and should be strongly considered when determining management protocols for loggerhead nesting beaches.