Changes in Loggerhead Sea Turtle Nesting Behavior on a Nourished Beach in Southeast Florida

Florida’s sandy beaches support the highest density of nesting loggerhead sea turtles (Caretta caretta) in the Western Hemisphere, regionally significant numbers of green turtles (Chelonia mydas), and regular nesting by leatherback sea turtles (Dermochelys coriacea), all of which are federally listed under the U.S. Endangered Species Act of 1973 (Stewart et al., 2011; Witherington, Bresette, and Herren, 2006; Witherington, Herren, and Bresette, 2006). Additionally, many Florida beaches are designated as critical habitat for the NW Atlantic population of the loggerhead sea turtle (Office of the Federal Register National Archives, 2014, §226.223) or are proposed as such for the North Atlantic green turtle. Maintaining the suitability of Florida’s sandy beaches as nesting habitat is vital to the recovery of all three species.

Most loggerhead nesting in Florida occurs along the central and southeast Atlantic coasts from Brevard through Broward Counties (Meylan, Shroeder, and Mosier, 1995; Witherington, Bresette, and Herren, 2006). In this region, approximately 223 km (67%) of oceanfront beaches have been designated by the Florida Department of Environmental Protection (FDEP) as critically eroded (FDEP, 2022), a term that qualifies local communities for state and federal funding to remediate erosion under Florida’s Strategic Beach Management Plan (FDEP, 2023). Beach restoration, the initial mechanical placement of sand on an eroded beach, and nourishment, the subsequent periodic placement of sand on a restored beach (often referred to as renourishment) have been widely used in Florida as an effective method for mitigating shoreline erosion and protecting upland development from tropical storms (Dean, 2002; National Research Council, 1995). More than a third of the beaches along Florida’s central and southeast coasts have been nourished under FDEP’s management authority (FDEP, 2023). Given the value of Florida’s beaches to local economies (Houston, 2013), that percentage can only be expected to grow as rising sea levels and the frequency and intensity of storms associated with climate change increase (Houston, 2020).

Sea turtle nesting habitat is reduced on eroded beaches, particularly those fronted by armoring structures, such as sea walls and rock revetments, which limit the landward extent of shoreline movement (Houston, 2020; Lyons et al., 2020; Mazaris, Matsinos, and Pantis, 2009). Beach nourishment is often touted as a means for increasing the quantity of nesting habitat on these eroding shorelines (Montague, 2008). However, more sand does not necessarily result in more nests (Steinitz, Salmon, and Wyneken, 1998). Nourishment-induced changes in physical beach characteristics, including sediment composition, compaction, and moisture content, can alter the suitability of nesting habitat (summarized by Crain, Bolten, and Bjorndal, 1995), while changes in the cross-sectional profile of the built beach from the waterline to the dunes, including width, elevation, and slope, can affect nesting behavior (Brock, Reece, and Ehrhart, 2007; Ernest and Martin, 1999; Trindell et al., 1998). Additionally, steep vertical escarpments (scarps), which often form as the beach equilibrates from a wide, flat profile to a more naturally sloping profile under the influence of hydrological forces (National Research Council, 1995), may prevent turtles from reaching suitable habitat farther landward (Bagley et al., 1994; Davis et al., 1994; Herren, 1999; Nelson and Blihovde, 1998; Nelson and Dickerson, 1988). Many of these effects have been largely ameliorated through requisite minimization measures now included in state and federal permits for nourishment projects. Fill material used on Florida beaches must now be compatible in grain size, color, and composition with native beach sands (Florida Administrative Code, Rule Chapter 62B-41; USACE, 2011). Following construction, the beach must be tilled if sediment compaction exceeds 35.2 kg/cm². Any scarps present at the end of construction must be leveled before the contractor leaves the site, and ongoing monitoring and scarp knockdowns are required prior to each nesting season for several years postconstruction. Yet, despite these advances, nesting success (percentage of all turtle emergences onto the beach that result in nests) continues to be affected on newly built beaches.

Nourishment projects in central and southeast Florida typically result in a wide, flat elevated berm between the dune and shoreline and a relatively steep slope from the waterline to the seaward edge of the berm (USACE, 2008). This cross-sectional beach profile often results in reduced nesting success during the first one or two nesting seasons following construction (Brock, Reece, and Ehrhart, 2007; Hays, 2012; Long, Angelo, and Weishampel, 2011; Rumbold, Davis, and Peretta, 2001; Steinitz, Salmon, and Wyneken, 1998; Trindell et al., 1998).

In addition to reduced nesting success, nest placement on traditionally built beaches typically differs from that on natural beaches. Whereas loggerhead nests on naturally sloped beaches are broadly distributed across the entire width of the beach or clustered near the dune, those on nourished beaches tend to be concentrated on the seaward edge of the built berm (Brock, Reece, and Ehrhart, 2007; Ernest and Martin, 1999; Hays, 2012; Herren, 1999; Trindell et al., 1998; Wood, 2004). Nests in this region of the beach are at increased risk of washout during storm events and profile equilibration. Thus, wide nourished beaches do not necessarily confer greater protection for incubating nests. Collectively, reduced nesting success and increased nest washout on nourished beaches reduce overall hatchling production.

In this study, a novel approach was used to examine how changes in the cross-sectional beach profile following a beach nourishment project affected loggerhead nesting success and nest placement. Results are intended to inform future project designs to improve nesting habitat suitability while maintaining protective shoreline functions.

The study site encompassed a 6.4-km-long stretch of beach on Hutchinson Island in Martin County, Florida (Figures 1 and 2). Annual averages of 762 loggerhead nests and 627 nonnesting crawls were recorded on this stretch of beach during the five year period immediately preceding the study. The beach was originally restored in the winter/spring of 1995–96 and was either partially or fully nourished in 2001, 2002, and 2005. Another full-scale nourishment event (the current study) was completed in the spring of 2013. The Martin County Shore Protection Project (SPP) was designed to deliver 123 m³ of sand per linear meter of shoreline. Sediment was borrowed from a nearby offshore shoal and hydraulically pumped onshore, where it was mechanically distributed. The built beach was designed to extend approximately 65 m from the base of the constructed dune to mean low water (MLW; see 2013 construction template in Figure 3).

Seven cells, each 0.61 km in length, were equally spaced along the length of the project area and separated from one another by 0.21 km (Figure 1). Data were collected from each cell throughout both the 2012 (prenourishment) and 2013 nesting seasons (March–September); data collection in 2013 did not begin until the beach was mechanically tilled to remediate potential sediment compaction and all construction equipment was removed from the beach. The seven study cells collectively included 4.27 km of oceanfront beach. During daily surveys, data were collected for all sea turtle emergences (crawls) onto the beach that were above the most recent high-water line (HWL). This included both nesting and nonnesting crawls (the latter commonly referred to as false crawls). However, only data for loggerhead sea turtles are presented in this paper.

All loggerhead nests within the seven cells were marked and monitored throughout their incubation periods in accordance with Florida Fish and Wildlife Conservation Commission (FWC) protocols (FWC, 2016). A nest was recorded as washed out if prevailing wave and tidal conditions caused erosion at the nest site and all nest markers were lost.

A key component of the study design was the collection and analysis of three-dimensional data to help identify those elements of the beach profile (i.e. width, slope, and elevation) that may influence a turtle’s decision to nest and/or where to place its nest on the beach. The location of each nesting and nonnesting loggerhead crawl was mapped using Trimble™ real-time kinematic (RTK) GPS instrumentation (Trimble R8 GNSS receivers and TSC3 controllers). These instruments provided survey-quality positional data capable of horizontal (latitude/longitude) and vertical (elevation) accuracies ≤3 cm. Instruments were routinely calibrated against established FDEP monuments of known elevation, and all data were independently reviewed and certified for accuracy by a contracted, professional surveyor (Geomatic Services, Inc., Palm City, Florida).

RTK GPS data were collected at the following points along each crawl: the point at which the ascending crawl intersected the most recent HWL, the clutch location on nesting crawls, the apex (most landward extent) of each nonnesting crawl, and the point at which the descending crawl intersected the most recent HWL. Additionally, GPS data were collected at the following shore-perpendicular points adjacent to the nest (as used throughout, nest implies clutch location) or crawl apex: ∼1 m landward, ∼1 m seaward, toe of the dune (TOD), and the most recent HWL.

Certain points along the crawl were considered indicative of a decisive action taken by the turtle. These “decision points (DPs)” were represented by either a nest or the apex of a nonnesting crawl. The latter represents the point at which a turtle decided not to nest and began its return to the ocean. To isolate effects of beach profile on nesting decisions, any turtle that encountered an escarpment at least 0.46 m in height (FWC, 2016) during its ascent of the beach, as well as any crawl with an abandoned dig, was eliminated from the analyses. Abandoned digs could be caused by human disturbances, buried objects, or other factors unrelated to the influence of beach profile on nesting behavior. Thus, the only crawls included in the analyses were those in which no major obstacles were encountered along the path of the crawl, and a decision was made to either nest or abandon the nesting attempt without any prior digging.

RTK GPS data were used to generate metrics for assessing loggerhead nesting decisions, including elevation at the DP, distance of the DP from both the HWL and TOD, and shore-perpendicular distance between the HWL and TOD (beach width). Beach width represents the amount of dry sandy habitat available to a turtle at its emergence site on the date of the crawl.

In 2012, the slope of the beach between the HWL and the DP was also examined, as was the slope at the DP (using points ∼1 m landward and seaward of the DP). Comparison of these two metrics allowed assessment of the change in slope as turtles neared their DP. All slopes were computed using the arctangent trigonometric function of rise (change in elevation) over run (straight-line distance) between two points of interest (e.g., HWL and DP). Insofar as short distances between two points can yield exaggerated slopes, any crawls with a DP within 1 m of either the HWL or TOD were eliminated from the analyses.

In 2012, there was no dramatic change in beach slope as turtles crawled from the HWL to the DP (see November 2012, Figure 3). The nourished beach in 2013 consisted of a wide, relatively flat berm, a shallow midbeach trough, and a relatively steep foreshore slope (FS). Depending on tidal stage, turtles emerging on this beach might experience two abrupt changes in slope as they ascended the beach, one as they crawled landward of the HWL and began scaling the FS, and the other as they transitioned from the FS onto the flat berm (see May 2013, Figure 3). Thus, for a DP located on the berm in 2013, a straight-line slope between the HWL and the DP, as computed in 2012, would not represent conditions experienced by a turtle during its beach ascent. Consequently, three additional distance and slope measurements were needed for the nourished beach: from the HWL to the base of the FS, from the base to the crest of the FS, and from the crest of the FS to the DP. Reliable RTK GPS measures were not available to accurately identify the base and crest of the FS, so light detection and ranging (LiDAR) data (collected on 8 July 2013 by Woolpert, Inc., Miami, Florida; http//:www.woolpert.com) were used as a surrogate. The LiDAR data were integrated with a subset of RTK GPS data collected over a 2 week period (26 June through 10 July) during peak nesting and encompassing the date of the overflight. In total, 84 nesting and 106 nonnesting loggerhead crawls were captured by this subset. Using the same logic applied to analyses of 2012 slope data, crawl distances <1 m between two points of interest (e.g., HWL to base of FS) were eliminated from the 2013 slope calculations.

The distance of a DP from the HWL divided by the corresponding beach width on the date of the crawl was used to calculate the percentage of available habitat utilized by a turtle before it nested or abandoned its nesting attempt. If a turtle crawled landward of the TOD, the nest or crawl apex was considered to have been placed at the TOD, and the turtle was considered to have utilized 100% of available habitat.

Most of the variables measured during this study did not lend themselves well to multivariate analyses because many were interrelated (multicollinearity), and they rarely had a linear relationship with nesting success (Hair et al., 2010). Consequently, each variable was analyzed independently using either a Welch’s t test or a generalized linear model (GLM), which is less sensitive to the two basic assumptions of analyses of variance, namely, data normality and homogeneity of variance (Nelder and Wedderburn, 1972).

GLM analyses were applied to variables for which comparable data were collected during both years of study: beach width, distance of the DP from the HWL, distance of the DP from the TOD, percentage of beach width used, elevation at the DP, and slope at the DP. The GLM used in this study incorporated regression analyses to test for significant differences between years for both crawl types combined and between crawl types for both years combined. In addition to these unique main effects, the GLM determines if there is an interaction effect between year and crawl type. A significant interaction indicates that the nourishment project affected the behavior of nesting and nonnesting turtles differently relative to the variable being analyzed (Jaccard and Turrisi, 2003). Within the GLM, a robust regression, which effectively accommodates outliers (Murphy, 2012), was used to examine interaction effects for all variables except percentage of beach width used, which was tested with beta regression (Ferrari and Cribari-Neto, 2004). All GLM analyses were performed using the “MASS” package in R™, version 4.3.2.

Welch’s t test (Welch, 1947), which adjusts for unequal variances and is robust to violations of the normality assumption (Derrick, Toher, and White, 2016), was used for testing means between crawl types when only a single year of comparable data was available. These tests, as well as regression analyses, were performed in Excel.

Each variable assessed during this study was also analyzed independently using binned logistic regression (BLR), a novel variation of logistic regression derived from the computer science field. BLR, which addresses the problem of nonlinearity (Motwani, Bacher, and Molstad, 2023), partitions data into equally sized bins and computes the odds and probability of a dichotomous outcome (e.g., nesting vs. not nesting) for each bin. To adequately address nonlinear data characteristics and maximize the explanatory power of the analyses, the bracket used for each bin must be appropriately sized (Lolla and Hoberock, 2011; Scott, 1979; Sturges, 1926). In this study, the bracket was set at one half the standard deviation of the mean computed for the combined range of values, excluding outliers, collected over both years of study. This convention relies on the standardized distribution of the data and satisfies the appropriate number of bins suggested by the Sturges model.

The odds ratio (OR) generated by BLR reflects nesting success and is simply derived by dividing the number of nests by the number of false crawls. When the numbers of both crawl types are equal, the OR is 1.0, and nesting success is equal to 50.0%. Ratios greater than 1.0 favor the odds of nesting, while those below favor the odds of not nesting. An exact binomial test (Kaempf, 1995) was used to determine significance of the OR for each bin. This test is based on a traditional two-tailed distribution with a 95% confidence interval around a hypothesized mean nesting success of 50%. BLR analyses were performed in R, version 4.1.3.

Unless specifically indicated otherwise, all results presented in this paper were derived from whole-nesting-season RTK GPS data. The abbreviated LiDAR data set was used only to obtain distance and slope metrics from the HWL to the DP in 2013.

After eliminating crawls with abandoned digs, scarp encounters, and other anomalies, 2191 loggerhead crawls were analyzed from the seven cells within the Martin County SPP over the 2 years of study (Table 1). This represented 91.3% of all nests and 71.5% of all nonnesting crawls in 2012 and 79.6% of all nests and 61.3% of all nonnesting crawls in 2013. (As is typical for loggerheads, abandoned digs and scarp encounters were more frequent on nonnesting crawls than on nesting crawls, and the incidence of scarp encounters for both crawl types was greater in 2013 than in 2012.) Based on these data, loggerhead nesting success declined from 65.6% in 2012 to 47.1% in 2013 despite similar numbers of total crawls each year.

Prior to nourishment, the average width of available nesting habitat at points where loggerheads (both crawl types combined) emerged from the ocean was 19.6 m (±7.31 m; N = 1042; range = 2.3–41.8 m). Following nourishment, the corresponding average beach width was 36.3 m (±5.04 m; N = 1102; range = 15.1–56.9 m), an increase of approximately 85%. Mean beach width at crawl sites was significantly greater in 2013 than in 2012 (Table 1). However, within each year, beach width did not differ significantly between emergence sites of nesting and nonnesting turtles. The absence of a significant interaction effect indicates that the wider beach resulting from the nourishment project was not directly responsible for differences in nesting behavior between nesting and nonnesting loggerheads.

The average loggerhead nest was placed 9.2 m from the most recent HWL in 2012, and that distance increased to 10.9 m in 2013 (Table 1). DPs for nonnesting individuals were, on average, 1.2 m farther from the HWL than those of nesting turtles in 2012 and 1.9 m closer in 2013. GLM results indicated that differences in mean DP location relative to the HWL differed significantly between years but did not differ significantly between crawl types. The interaction effect was not statistically significant, indicating that the project did not affect the location of DPs relative to the HWL differently between nesting and nonnesting turtles.

A much larger change in loggerhead nest placement was evident between years when the location of DPs was assessed relative to the TOD. Following nourishment, the average nest was more than twice as far from the TOD as during the preceding year (Table 1). Thus, relative to the TOD, nest placement differed significantly both between years and between crawl types. A significant interaction effect indicated that the nourishment project affected the location of DPs relative to the TOD differently for nesting and nonnesting loggerheads.

In 2012, the distribution of loggerhead nests within available habitat (i.e. mean beach width) was more normally distributed than in 2013, with the average individual traversing approximately 50% of available habitat before nesting (Table 1; Figure 4). In 2013, the distribution of nests was heavily skewed toward the waterline, with nesting loggerheads traversing an average of only 30% of available habitat on the date of the crawl; 66% of all nests in 2013 were located within 10 m of the HWL. GLM analysis indicated that loggerheads used a significantly smaller percentage of beach width in 2013 than in 2012, and the percentage of beach used differed significantly between crawl types (Table 1). A significant interaction between years and crawl types indicates that the project was responsible for differences in the amount of available habitat utilized by nesting and nonnesting loggerheads.

Mean elevations at loggerhead DPs ranged from 2.08 on nonnesting crawls in 2013 to 2.59 m on nesting crawls in 2012 (Table 1). Elevations at DPs differed significantly both between years and between crawl types. However, the lack of a significant interaction effect indicates that changes in elevation associated with the project did not affect a turtle’s decision to nest or abandon its nesting attempt.

Mean slope at loggerhead DPs ranged from 3.42° at nonnesting DPs in 2013 to 6.46° at nest sites in 2012 (Table 1). This slope metric was significantly greater in 2012 than in 2013 and significantly greater at nesting than at nonnesting DPs. A significant interaction effect indicates that slope at the DP resulting from the project was responsible for observed differences in nesting behavior between nesting and nonnesting loggerheads.

In 2012, the mean slope from the HWL to the DP for nesting (6.7°) and nonnesting (6.0°) loggerheads was relatively small but statistically significant (Welch’s t = 4.218, df = 676, p < 0.001). As turtles continued to crawl landward and approached to within 1 m of their DPs, the slope leveled off slightly, changing by only −0.15°at nest sites and −0.71° at nonnesting DPs. Yet, this small difference was also statistically significant (Welch’s t = 2.554, df = 319, p = 0.011). Despite the general similarity of mean slope values at nesting and nonnesting crawl sites in 2012, there was considerable variability depending on location within the study area, sea state, and tidal stage at the time and on the date of the crawl.

In 2013, turtles emerging from the ocean experienced abrupt changes in beach profile as they crawled toward their DP (see May 2013, Figure 3; Figure 5). Based on data derived from the abbreviated LiDAR data set (N = 190), the average straight-line distance and slope from the HWL to the base of the FS were 4–5 m and <5°, respectively, with no significant difference in either distance or slope between nesting and nonnesting loggerhead crawls (Table 2). Once on the FS, turtles encountered a slope of approximately 14°. Neither the slope, nor the horizontal distance from the base to the crest, nor the height of the FS differed significantly between crawl types.

Loggerheads scaling the FS in 2013 encountered a relatively flat berm (Figure 5), with the average DP located 5–7 m landward of the crest (Table 2). Although the mean distance of the DP from the FS crest did not differ significantly between crawl types, the mean slope between those two points did (Table 2). The average nonnesting loggerhead experienced a slightly negative slope (mean = −0.5°), and the average nesting turtle experienced a slightly positive slope (mean = 0.8°). Nesting occurred on 67% of loggerhead crawls extending landward of the FS crest along a positive slope, whereas 62% of crawls along a negative slope resulted in abandoned nesting attempts.

Distances of loggerhead nests from both the HWL and TOD in 2012 produced significant results when regressed against beach width (F = 124.5 and 1075.5, respectively, df = 691, p < 0.001), although distance from the TOD (Figure 6A) produced a much stronger coefficient of determination (R² = 0.61 vs. 0.16). There was also a significant (F = 140.2, df = 703, p < 0.002), although relatively weak (R² = 0.20), correlation when the distance of nests from the HWL was plotted against slope to the HWL (Figure 6B).

In 2013, there was little discernible pattern (R² = 0.03) when distance of nests from the HWL was plotted against beach width, even though a polynomial regression was statistically significant (F = 10.8, df = 515, p = 0.001). As for 2012, a stronger relationship was found when beach width in 2013 was correlated with distance of the DP from the TOD (F = 62.4, df = 515, p < 0.001), yet the correlation coefficient remained weak (R² = 0.11).

Elevation was significantly correlated with distance of loggerhead DPs from the HWL in both 2012 (F = 413.6, df = 1074, p < 0.001; R² = 0.28) and 2013 (F = 966.2, df = 1289, p < 0.001; R² = 0.43). However, the cross-sectional profile of the beach differed substantially between years (Figure 5). In 2012, beach slope increased steadily across the HWL – TOD axis, whereas on the newly nourished beach, elevation increased rapidly over the first approximately 7 m and then was relatively flat from 7 to about 20 m landward of the HWL. Beyond 20 m, slope began increasing again, although gradually, toward the TOD.

Only 2.8% (20) of all loggerhead nests marked during 2012 were washed out compared with 9.8% (51) in 2013. On average, nests washed out in 2012 were located 5.1 m landward of the HWL at a mean elevation of 2.6 m. Comparable metrics for 2013 were 4.0 and 2.0 m, respectively. The mean distance of washed-out nests from the HWL did not differ significantly between years (Welch’s t = 1.750, df = 30, p = 0.090), but mean elevation did (Welch’s t = 4.501, df = 29, p < 0.001).

Average wave heights during the inclusive period when any loggerhead nests were on the beach did not differ significantly between years (2012 = 0.84 m, N = 188; 2013 = 0.80 m, N = 185). During that period, wave heights exceeded 2.0 m on 7 days in 2012 but only 2 days in 2013, with maximum wave heights of 3.9 and 2.4 m, respectively. No tropical storm or severe weather activity impacted the Martin County SPP during either nesting season. Nest loss in 2013 occurred sporadically throughout the nesting season, with peaks in mid-September and early October, both periods of moderate wave height (<1.3 m; Figure 7). In contrast, 75% of the nest loss in 2012 occurred over a 3 day period in late August following a day of wave heights exceeding 2.3 m.

Although GLM analyses highlight the relative importance of certain variables in affecting loggerhead nesting behavior, they are based on comparisons of mean values. They are not prescriptive of design changes that might improve the odds of nesting on built beaches. The BLR analyses, results of which are summarized in Table 3, provide that critical information.

In 2012, loggerheads had significantly higher odds of nesting than abandoning their nesting attempts if the DP was located between 2.3 and 17.2 m from the HWL, with the highest odds falling in the range of 9.7 to 13.5 m; individuals in that range were nearly three times more likely to nest than to false crawl. The only range associated with significant odds of not nesting in 2012 included the relatively few crawls (N = 16) terminating between 24.6 and 28.3 m from the HWL. Those individuals were more than four times more likely to false crawl as they were to nest. Collectively, nesting success in 2012 was only 34.0% for all loggerheads with DPs more than 17.2 m from the HWL (Appendix Table A2).

In 2013, the likelihood of nesting for loggerheads terminating their crawls on the seaward portion of the beach was reversed from that found in 2012 (Table 3). Three categories of DPs within 17.2 m of the HWL had significant odds of not nesting, with the lowest OR (0.283; nesting success = 22.1%) falling in the range of 13.5 to 17.2 m. Conversely, several categories greater than 17.2 m from the HWL had significant odds of nesting. The relatively few loggerheads (N = 24) terminating their crawls 24.6 to 28.3 m from the HWL were 11 times more likely to nest than to false crawl. The collective nesting success for all loggerheads with DPs more than 20.9 m from the HWL (11.0% of all crawls in 2013) was 74.4% (Appendix Table A2).

When assessing loggerhead nesting success relative to distance of the DP from the TOD, all individuals terminating their crawls within 23.4 m of the dune in 2012 had significant odds of nesting (Figure 8). However, the highest odds of nesting (OR = 3.250; nesting success = 76.5%) were associated with distances in the range of 11.7 to 17.5 m (Table 3). Although no range for this variable in the 2012 BLR analysis was associated with significant odds of not nesting, a finer analysis of DPs within 5.84 m of the dune, which encompassed nearly a third of all crawls (Appendix Table A3), revealed a different picture. Loggerheads crawling to within <1.0 m of the TOD (N = 110) had a nesting success of only 25.5%. Nesting success was reduced even further for DPs at or landward of the TOD (N = 66; nesting success = 22.7%).

In 2013, only those relatively few loggerhead crawls terminating in the range of 5.8 to 11.7 m from the TOD (N = 45; 4.1% of all crawls) had significant odds of nesting (Figure 8). Those individuals were 14 times more likely to nest than to false crawl (nesting success = 93.3%; Table 3). Conversely, three categories greater than 17.5 m from the TOD in 2013 were associated with significant odds of not nesting, with the lowest OR (0.483; nesting success = 32.6%) falling in the range of 17.5 to 23.4 m (Figure 8; Table 3).

The only comparable slope metric for both years was slope at the DP. Both prior to and following nourishment, loggerheads with DP slopes in the range of 2.4° to 14.3° were four to five times more likely to nest than to abandon their nesting attempt, although the percentage of crawls falling within that range was considerably greater in 2012 than in 2013 (Table 3). No DP slope category was associated with significant odds of not nesting in 2012, while several DP slope categories less than –0.6° and greater than 20.2° were significantly skewed toward false crawls in 2013. Collectively, only six of the 58 loggerhead crawls (nesting success = 10.3%) in 2013 terminating at slopes greater than 20.2° resulted in nests (Appendix Table A4). Nesting success was also very low (27.2%) for crawls (N = 382) with negative DP slopes. None of the 25 loggerheads with DP slopes greater than 23.2° or less than –3.5° (N = 29) nested.

When looking at the overall slope from the HWL to the DP in 2012, loggerheads ascending the beach at locations with a slope in the range of 4.0° to 11.1° (85.2% of all crawls) had significant odds of nesting (Table 3). Within that range, odds of nesting increased steadily as slopes increased; turtles in the two upper categories (8.7° to 11.1°) were over three times more likely to nest than to false crawl (nesting success = 76.9%; Appendix Table A5). There were no categories of slope from the HWL to the DP in 2012 associated with significant odds of not nesting.

Change in slope as loggerheads neared their DP also affected nesting decisions. In 2012, shifts in the range of –4.8° to 4.3° (90.3% of all crawls) were significantly more likely to result in nests than in abandoned nesting attempts (Table 3). As for overall slope from the HWL to the DP, the greater the change in slope in a positive direction, the greater the odds of nesting (Appendix Table A6). Turtles that experienced a change in slope of 2.8° to 4.3° (N = 75) as they crawled to within 1 m of their DP were nearly 10 times more likely to nest than to false crawl (nesting success = 90.7%). No change in slope ranges in 2012 produced significant odds of not nesting.

Elevations in the range of 2.1 to 3.2 m (65% of all crawls) were associated with significant odds of nesting in 2012 (Table 3). At lower (range = 0.9 to 1.5 m; N = 33) and higher (range = 3.5 to 3.8 m; N = 43) elevations, representing areas closest to the water and dune, respectively, loggerheads were significantly more likely to abandon their nesting attempts. There was some overlap in this pattern in 2013, as the relatively few loggerheads (N = 23) making nesting decisions at elevations in the range of 2.7 to 3.2 m were more than six times more likely to nest than to false crawl. Collectively, the 80 turtle crawls with DPs at elevations greater than 2.7 m in 2013 had a nesting success of 71.3% (Appendix Table A7). Conversely, several ranges in 2013 containing DP elevations <2.4 m were associated with significant odds of not nesting. At elevations <1.5 m, nesting success in 2013 was only 20.1%, and no turtles nested at elevations <0.9 m during either year.

In 2012, loggerheads traversing between 20% and 90% of beach width (75.3% of all crawls) had significant odds of nesting (Table 3). The highest OR was associated with the group having DPs near midbeach (range = 50%–60%; nesting success = 83.6%). The only significant odds of not nesting in 2012 were for those relatively few turtles (12.6% of all crawls) that crawled closest to the dune (range = 90%–100%; N = 131; nesting success = 22.7%). On the newly built beach in 2013, most turtles that crawled landward through no more than 50% of available habitat had significant odds of not nesting, with odds decreasing as they approached midbeach (Appendix Table A8). However, for those loggerheads that crawled landward of the midbeach trough (N = 149), nesting success increased to 72.5%, with those traversing 60%–90% of beach width having significant odds of nesting (N = 74; nesting success = 87.8%).

Historically, beach nourishment projects along Florida’s central and southeast coasts typically resulted in a wide, flat, elevated berm (Brock, Reece, and Ehrhart, 2007; Ernest and Martin, 1999; Wood, 2004). It would seem logical that a wider beach would expand sea turtle nesting habitat and thereby enhance nesting. National recovery plans for sea turtles acknowledge that beach nourishment can improve nesting habitat in areas of severe erosion and “is generally viewed as less harmless to sea turtles than beach armoring (NMFS and USFWS, 2008). However, as demonstrated during this study, the simple creation of potential nesting habitat through the mechanical placement of sand on the beach does not necessarily increase nesting. The altered suite of environmental variables associated with a change in beach profile on the nourished beach reduced nesting and nesting success, affected nest placement, and most importantly, increased the risk of nest washout.

A reduction in sea turtle nesting success is almost universally reported in the first to second year following nourishment (Brock, Reece, and Ehrhart, 2007; Hays, 2012; Long, Angelo, and Weishampel, 2011; Rumbold, Davis, and Peretta, 2001; Steinitz, Salmon, and Wyneken, 1998; Trindell et al., 1998). Loggerhead nesting success within the Martin County SPP declined by approximately 19 percentage points following nourishment. This decline cannot be attributed to a higher incidence of scarp encounters, as those crawls were eliminated from the analyses, nor did the decline in nesting success result from fewer loggerheads coming ashore, as similar numbers of crawls were documented during both years of study. Rather, the proportion of crawls resulting in nests declined, as 27% fewer nests were documented in 2013 (Table 1). Loggerheads simply found the newly nourished beach with its notable change in profile less attractive as nesting habitat than the naturally contoured beach that preceded nourishment.

There was a distinct difference in the location of loggerhead nests relative to beach width before and after nourishment (Figure 4). In 2012, the “average” nest was placed in the middle third of available habitat on the date of the crawl, whereas in 2013, nests were heavily skewed toward the waterline despite a beach that was 85% wider. The beach profile in 2012 is representative of a naturally contoured beach, having had 7 years to equilibrate since the last nourishment project, and the shore-perpendicular distribution of loggerhead nests observed that year was similar to the distribution reported for other high-density nesting beaches along Florida’s southeast coast (Gravelle and Wyneken, 2022).

Before examining changes in nest placement resulting from the Martin County SPP, factors affecting nesting decisions on the naturally contoured beach should first be considered, as nest placement has important consequences for hatchling production and survival (Bjorndal and Bolten, 1992; Hays and Speakman, 1993; Miller, Limpus, and Godfrey, 2003; Wood and Bjorndal, 2000). Competing selective forces favor against placing the nest too far landward or too close to the water line. A site must be selected sufficiently far from the HWL to minimize risk of tidal inundation or washout. Yet, there is an increased energy demand and higher risk of predation the farther landward the nesting female crawls. If the nest is placed too close to dune vegetation, the risk of root invasion increases (Conrad et al., 2011). Survival may also be reduced for hatchlings emerging from nests close to the dune, as they have farther to crawl to reach the ocean and are therefore more vulnerable to predation than those emerging closer to the water (Erb and Wyneken, 2019). Along Florida’s southeast coast, midbeach placement coupled with a hot and humid subtropical climate seem to provide a “Goldilocks” incubation environment producing highly successful loggerhead nests (Gravelle and Wyneken, 2022).

As adult sea turtles emerge from the ocean and ascend the beach, various endogenous and exogenous cues, including thermal, olfactory, visual, tactile, and energetic, presumably act independently or in concert to influence nesting decisions (Miller, Limpus, and Godfrey, 2003; Salmon et al., 1995; Wood and Bjorndal, 2000). These may be constantly, or at least periodically, assessed as the turtle crawls away from the ocean and toward the dune, and the combination and relative strength of available cues may change along this path. Consequently, identification of a specific cue or set of cues affecting nesting decisions has been elusive. Nevertheless, beach slope seems to be the most influential of cues evaluated to date (Hays, 2012; Long, Angelo, and Weishampel, 2011; Wood and Bjorndal, 2000).

Beach slope appears to be predictive of local and regional differences in loggerhead nest densities (Provancha and Ehrhart, 1987; Yamamoto et al., 2012). Odds of loggerhead nesting on the naturally sloped beach at the Martin County study site were significant within the range of approximately 4° to 11° and increased as slope within that range increased.

Hays (2012) found that a factor equally important as overall slope from the HWL to the DP is a gradual slope increase over the second half of the crawl. Similarly, Wood and Bjorndal (2000) found that the steepest slope along the path of the loggerhead crawls they analyzed was at the nest site. Results of BLR analyses conducted during the current study support prior findings. As turtles approached to within 1 m of their DP, odds of nesting increased as the change in slope increased. Loggerheads encountering an increase in slope in the range of 2.8° to 4.3° were nearly 10 times more likely to nest than to false crawl. However, on the prenourished beach, even decreases in slope as much as 4.8° were associated with significant odds of nesting. Thus, loggerheads may be responding favorably to any change in slope, positive or negative, as they approach their DP, although relatively large increases appear to have the greatest effect. It is important to note that what are perceived by humans as minor changes in slope (<5°) may be very perceptible to a large, heavy animal out of its natural environment.

One explanation for why steeper slopes may increase the odds of nesting is that turtles have to crawl shorter distances to reach elevations sufficient to protect their nests from tidal impacts. During the present study, elevation increased as distance of DPs from the HWL increased (Figure 5), and turtles ascending relatively steep slopes tended to place their nests closer to the HWL than those ascending more modest slopes (Figure 6B). Maurer and Johnson (2017) also found loggerhead crawl distance and beach slope to be inversely related on the Mississippi barrier islands, while elevation was shown to positively influence loggerhead nest placement in Brevard County, Florida (Hays, 2012) and in Greece (Katsilidis et al., 2013). Thus, on naturally sloped beaches in southeast Florida, distance of the DP from the HWL, slope, and elevation at the DP are all interrelated. However, given the considerable scatter in regression data and the relatively low correlation coefficients, other variables are also likely to contribute to nesting decisions.

The amount of energy expended by a turtle crawling up the beach is an overlooked component of nesting behavior simply because it is difficult to measure. Maurer and Johnson (2017) found loggerhead crawl distance from the waterline to the DP to be inversely correlated with beach slope, and it is logical that energy expenditures would increase as slope increases. However, this does not preclude the involvement of other factors in nest placement. For example, dune features may influence nesting behavior (Camhi, 1993; Hays and Speakman, 1993; Mazaris, Matsinos, and Pantis, 2009; Salmon et al., 1995; Witherington, Hirama, and Mosier, 2011). At the Martin County study site, there was a highly significant positive correlation between beach width and the distance of loggerhead nests from the TOD. However, nesting success declined dramatically for loggerheads that crawled to within 5.8 m of the dune. Loggerheads crawling within the final 10% of available beach width on the date of the crawl were nearly 2.5 times more likely to abandon their nesting attempt than to nest (Appendix Table A8). Similarly, Witherington, Hirama, and Mosier (2011) found that loggerheads approaching a 1-m-high experimental vertical structure placed on a beach in southern Brevard County nested on average 3.5 m farther seaward than individuals on the same beach when the structure was absent. Thus, proximity to the dune may be important in affecting nesting behavior, but if it alone was responsible for nest placement, nests would assume a more uniform shore-parallel distribution along the beach.

Although loggerhead nests on the naturally sloped beach were most prevalent in the middle portion of the beach on the date of the crawl, they were spread throughout all available habitat (Figure 6A). Several explanations may account for this phenomenon: (1) Not all turtles are responding similarly to available exogenous cues; (2) there is considerable spatial/temporal variability in the strength of available cues; (3) turtles may be responding to multiple cues (supported by this study; Long, Angelo, and Weishampel, 2011; Mazaris, Matsinos, and Margaritoulis, 2006; Wood and Bjorndal, 2000); (4) individual turtles adjust nest placement to higher locations based on past nesting experience (Pfaller, Limpus, and Bjorndal, 2009; Tucker, 2010); or (5) endogenous cues may be responsible for observed patterns (Hays et al., 1995; Wood, 2004).

In Florida, an individual loggerhead turtle produces multiple clutches each nesting season, with an average renesting interval of approximately 2 weeks (Tucker, 2010; Witherington, Herren, and Bresette, 2006). The 2 week gap between nesting events would place the HWL at distinctly different locations relative to beach width based on time of emergence, lunar phase, and sea conditions. Individual loggerhead turtles spread their nests along the HWL-TOD axis on successive nesting attempts (Camhi, 1993; Hays and Speakman, 1993; Pfaller, Limpus, and Bjorndal, 2009). This strategy mitigates the risk of catastrophic reproductive failure that might befall nests if they were all concentrated in one location. Some have suggested that a species-specific crawl distance above a vacillating tide line could account for this scatter (Hays et al., 1995; Wood, 2004), although other profile variables clearly contribute to nesting decisions at the Martin County study site.

The variability regarding nest placement relative to the tide line argues for the use of static reference points when assessing nest placement across the HWL-TOD axis (Pfaller, Limpus, and Bjorndal, 2009). In the Martin County study, there was a much stronger correlation coefficient when assessing nest location relative to beach width when using the TOD rather than the HWL. Regardless of the exact mechanism(s) affecting nest placement on the naturally sloped beach, there was a clear shift in patterns following nourishment.

The cues that increased the odds of loggerhead nesting on the naturally sloped beach in 2012 were either generally absent on the wide, flat built beach or were replaced with cues that had the opposite effect. Both nesting and nonnesting loggerheads used a significantly smaller percentage of available habitat (beach width) in 2013 (Table 1). Furthermore, nonnesting turtles explored more available habitat than nesting turtles in 2012 but less in 2013. This suggests that in 2012, individuals that had not yet nested were receiving positive habitat suitability cues and crawled farther landward before ultimately deciding to abandon their nesting attempt, whereas on the built beach, many individuals made a negative assessment of habitat suitability relatively early into their crawls. Even most nesting turtles exhibited relatively little interest in exploring the expanded habitat available to them. GLM analyses indicated that these differences in loggerhead nesting behavior between years and crawl types can be attributed to the nourishment project.

The major changes in beach profile associated with the nourishment project were a steep FS and a relatively flat berm. Soon after turtles emerged from the ocean and crawled beyond the HWL, they were met with a FS of approximately 14° (Table 2). That was more than double the slope encountered on the naturally sloped beach (mean = 6.4° ± 2.8° for both crawl types combined; N = 1067). Most loggerheads that terminated their crawls on the relatively flat portion of the beach seaward of the FS did not nest. This suggests that the steep FS landward of emergence sites may have presented a visual deterrent for some turtles.

As noted earlier, loggerheads approaching an experimental, 1-m-high, vertical structure on a beach in central Florida nested on average 3.5 m farther seaward than individuals on the same beach when the structure was absent (Witherington, Hirama, and Mosier, 2011). The mean height of the 2013 FS in the Martin County study was slightly greater than 1 m (Table 2), and although a 14° slope is far from a vertical wall, it may be perceived as one from the perspective of an adult female loggerhead whose head is only 25 cm or so above the sand. Insofar as relatively little dry sandy beach was present seaward of the FS, the majority of individuals declining to ascend the relatively steep slope returned to the ocean without nesting. The lack of a discernible dune feature for turtles failing to scale the FS may also be a factor, as these turtles were presented with a uniform dark horizon contrasted with an overlying brighter open sky.

Aside from the visual presence of the FS, both nesting and nonnesting turtles were exposed to similar beach profiles in 2013. There were no significant differences between crawl types in distance or slope from the HWL to the base of the FS, distance or slope from the base to the crest of the FS, or height of the FS (Table 2). Differences between crawl types began to emerge only after turtles transitioned onto the flat berm. The likelihood of nesting was greatest for turtles crawling on a slightly positive slope landward of the FS, while those encountering negative slopes were much more likely to abandon their nesting attempts. Other researchers have similarly found a flattening of the beach following nourishment to reduce loggerhead nesting success, and the greater the change in slope from a natural profile, the greater the effect (Hays, 2012; Long, Angelo, and Weishampel, 2011).

Results of the GLM analyses indicated that slope at the DP, the only comparable slope metric for both years, differed significantly between years and crawl types, and those differences can be attributed to the nourishment project (Table 1). The relative importance of slope in loggerhead nesting decisions was further supported by results of the BLR analyses. Both the range of DP slopes producing significant odds of nesting (2.4° to 14.3°) as well as the ranges associated with the highest odds of nesting (5.4° to 11.3°) were the same before and after nourishment (Appendix Table A4). Nesting success for the cohort encountering these favorable slopes in 2013 was 72% compared with 47% for the entire sampled population. Conversely, turtles encountering negative slopes at their DP in 2013 had significant odds of not nesting; for individuals with DP slopes less than −0.6°, nesting success was only 27.2%. The apparent effects of negative slopes on the relatively flat nourished beach in 2013 coupled with the general absence of negative slopes in 2012 likely account for much of the disparity in nesting success between years.

Although positive slopes were associated with significant odds of nesting during both years, excessive slopes in 2013 had a negative effect. On the nourished beach, loggerheads experiencing slopes at their DP exceeding 20° had significant odds of not nesting, and nesting success fell to 10.3% (Appendix Table A4). Thus, it appears that there is a sweet spot for the inducement of loggerhead nesting in the range of 2.4° to 14.3°. However, based on observations of nest distributions on the naturally sloped beach, slope likely does not act independently of other cues, such as distance from the TOD, presence of elevated dune features, and/or energy expended ascending the beach. For example, the added energy required to scale the relatively steep FS in 2013 may explain why most loggerheads utilized only a small portion of the new habitat available to them (Wood, 2004).

Change in slope also seems to be important in affecting nesting decisions. In 2012, changes in slope in the range of −4.8° to 4.3° as loggerheads crawled to within 1 m of their DP were associated with significant odds of nesting (Table 3). However, in 2013, turtles transitioning from the FS onto the flat berm experienced changes in slope greater than 13°, and yet the average nest was nearly 7 m landward of the FS. This might be explained as loggerheads having an innate tendency to crawl a set distance from the waterline before nesting, as advanced by Hays et al. (1995) and Wood (2004), or perhaps they must crawl a certain distance before slope, changes in slope, and/or other factors trigger nesting. Clearly, several variables are at play, and the influence of any particular variable may differ depending on a turtle’s location on the beach.

The Martin County SPP widened the beach by 16.5 m, but loggerhead nests in 2013 were on average only 1.7 m farther landward of the HWL than in 2012 (Table 1). Thus, loggerheads were using only 10.3% of the new habitat available to them on the built beach. As a result, nearly three quarters of all nests in 2013 were located on the seaward-most third of the beach. Additionally, despite the large volume of sand placed on the beach, the average nest in 2013 was at a significantly lower elevation than in the year prior to nourishment. This change in nest placement and beach morphology placed incubating eggs at increased risk of washout.

Newly nourished beaches in southeast Florida undergo considerable reconfiguration during periods of turbulent sea conditions, as seaward sections are eroded, and the beach transitions from a wide, flat profile to a narrower beach with a relatively uniform slope from the HWL to TOD (i.e. profile equilibration). Differences are clear when comparing the cross-sectional survey profile of the Martin County SPP immediately postconstruction (May 2013) with the naturally sloped beach that preceded nourishment (see November 2012, Figure 3). Nests present on seaward portions of a nourished beach are particularly vulnerable to washout during storms and profile equilibration.

At the Martin County study site, only 2.8% of all loggerhead nests were washed out in 2012 compared with 9.8% of nests on the newly built beach in 2013. Considering that fewer nests were present in 2013, the percentage of all nests washed out was 3.5 times greater than in 2012. Higher nest loss on the nourished beach was unrelated to prevailing wave climate, as mean daily wave heights were similar between years, and the frequency of the highest waves was greater in 2012 than in 2013. Considerable resources are targeted toward minimizing impacts to sea turtle nests during construction of beach nourishment projects. Minimization of nest washouts on newly constructed beaches should be given equal if not greater weight in the design of future projects.

Ideally, the postequilibrium cross-sectional profile of a nourished beach should, to the extent possible, mimic the profile of preexisting or adjacent, noneroded beaches (Brock, Reece, and Ehrhart, 2007; Long, Angelo, and Weishampel, 2011; Reine, 2022). This objective is supported by data collected during the current project. The 63% loggerhead nesting success recorded in 2012 is indicative of a good nesting environment, as, statewide, this species typically completes only about half of its nesting attempts (Witherington et al., 2009).

The average beach slope from the HWL to loggerhead nest sites at the Martin County SPP in 2012 was 6.7°. Significant odds of nesting occurred within the range of 4° to 11° (Appendix Table A5), with highest odds at the upper end of that range (9° to 11°). Coincidentally, high-density nesting beaches at the Kennedy Space Center and Archie Carr National Wildlife Refuge on Florida’s central east coast have reported average slopes of 9° (Provancha and Ehrhart, 1987; Wood and Bjorndal, 2000). Collectively, these data suggest that postequilibrium slopes in the range of 6°–9° may be appropriate for many beaches in central and southeast Florida. However, local conditions typically preclude agencies from incorporating the desired postequilibrium slope into the construction template for a project. Thus, the objective should be to build beaches with as much slope as possible from the waterline to the dune.

Engineering designs for nourishment projects present slopes as a ratio expressing rise over run. The traditional construction template for nourishment projects in southeast Florida consists of a 1:10 (5.7°) or 1:15 slope (3.8°) at the seaward edge of sand placement and an elevated, flat (no slope) berm from the seaward slope to the dune (USACE, 2008). This design maximizes the amount of sand placed above the mean high-water line (a major consideration for taxpayers and beachgoers), meets requisite state and federal shore-protection cost-benefit criteria, facilitates calculation of contracted fill volume during construction, and minimizes the amount of final mechanical grading required postconstruction (PBS&J and EAI Staff, 2007). In an effort to improve the suitability of sea turtle nesting habitat on nourished beaches, FWC in consultation with FDEP and the U.S. Army Corps of Engineers has experimented with alternative construction templates. However, to date, the efficacy of those alternative designs has been more anecdotal than empirical in the absence of adequate monitoring and/or sample sizes.

When considering design changes for future beach nourishment projects, it is recognized that eligibility for state and/or federal cost-sharing is contingent upon meeting a suite of cost-benefit criteria. The project must provide an acceptable level of shoreline protection in relation to construction costs. A key factor among those criteria is the volume of sand placed on the beach. Meeting the sand quantity threshold while maintaining a “natural” slope along an eroded shoreline would require placing a considerable amount of material below MLW. In some instances, particularly along the southeast coast of Florida, potential impacts to submerged hardbottom resources are often prohibitive. Additionally, there are limitations on the height of constructed dune features. Thus, the seaward limit of sand placement and the maximum landward height of a project may be constrained by environmental and regulatory barriers, and within a given footprint, a sloped beach holds less volume of sand than a high, flat beach. Consequently, volumetric requirements of nourishment projects tend to favor flat beaches.

Although the construction template for the 2013 Martin County SPP incorporated a 1:50 berm (1.2°) slope and a 1:20 slope (2.9°) from the seaward edge of the berm to MLW (Figure 3), the postconstruction slope for loggerheads that crawled landward of the FS averaged less than 1.0° and was often negative. The accumulation of sediment at the seaward edge of the berm during profile equilibration and associated midbeach trough are evident in postconstruction profiles of the Martin County SPP (see May 2013, Figure 3). Thus, in addition to design specifications, site-specific equilibration processes must be considered during project planning, as beach profile may undergo appreciable and relatively rapid changes following construction.

Based on results of the Martin County study, a continual slope from the waterline to the dune is recommended for southeast Florida beaches. However, when volumetric requirements disallow such a design, the slope of the constructed berm should deviate as much as possible from horizontal. This will minimize the potential formation of a midbeach trough and associated negative slopes landward of the FS, as this study clearly demonstrated the disparity in nesting behavior when loggerheads encountered either positive or negative berm slopes.

Any change in the construction template for the Martin County SPP, as well as associated changes to beach profile resulting from local equilibration forces, including scarping, must be evaluated, and adjustments should be made based on observed turtle responses. Additionally, research is needed to ensure that changes to construction templates that may benefit loggerhead turtles do not negatively impact other species, which may differ in nesting behavior (Brock, Reece, and Ehrhart, 2007). Ultimately, site-specific designs will likely be derived through trial and error. Furthermore, construction templates for southeast Florida may not be appropriate for other locations. Different cues may influence nesting decisions on beaches with different cross-sectional profiles, particularly on beaches that tend to be naturally flatter and/or wider than those in southeast Florida (Garmestani, Percival, and Rice, 2000). Similar analyses will be required to refine nourishment construction templates for those beaches. However, it is evident that beach nourishment projects, as currently constructed on Florida’s high-density nesting beaches, have negative impacts on loggerhead sea turtle nesting and place proportionately more nests at risk of washout. Although those impacts tend to ameliorate within 1 or 2 years (Brock, Reece, and Ehrhart, 2007; Rumbold, Davis, and Peretta, 2001; Trindell et al., 1998), efforts to enhance nesting habitat rather than simply expanding potential habitat should continue.

This appears to be the first time that three-dimensional RTK GPS data have been used to comprehensively study sea turtle nesting patterns over the course of an entire nesting season. Results demonstrate the efficacy of this system in collecting a large amount of data along the paths of crawls and placing that information into context with relevant beach features. Additionally, most studies of sea turtle nesting behavior have focused on nest placement and reproductive success. In addition to looking at where turtles place their nests, it is equally important to look at places where they do not (Hays et al., 1995; Miller, Limpus, and Godfrey, 2003).

The nourished beach in 2013 presented turtles with a dramatically different cross-sectional profile than the naturally sloped beach that preceded nourishment. Although similar numbers of loggerhead crawls occurred during both years, fewer nests were placed on the nourished beach. The decline in nesting cannot be attributed to the presence of escarpments, as crawls that contacted scarps were eliminated from analyses. On the nourished beach, loggerheads tended to place their nests along the seaward-most portion of the built berm, utilizing only 10.3% of the newly available habitat. Nests closest to the waterline were at increased risk of washout as the beach equilibrated to a more natural profile; the percentage of loggerhead nests washed out in 2013 was 3.5 times greater than the number washed out in 2012. These findings are essentially unchanged from results of a similar study conducted by the lead authors in 1995–96 during the initial restoration of the Martin County SPP (Ernest and Martin, 1999).

There is compelling evidence that beach nourishment projects along Florida’s central and southeast coasts have negatively affected nesting loggerhead sea turtles during the first to second year postconstruction. To date, no design changes or related construction practices have effectively ameliorated these impacts. A steeper, more uniform slope from the MLW to TOD is suggested for future projects. To meet regulatory volumetric requirements, this may dictate that a larger volume of sand be placed seaward of the MLW than traditionally has occurred. Where environmental constraints limit seaward placement and construction, and/or where subsequent equilibration processes are likely to result in a relatively steep FS, a positive and continual slope from the predicted crest of the FS to the TOD should be included in the design. The postconstruction berm slope should deviate as much possible from horizontal to avoid negative berm slopes. It is recognized that a universal construction template would not be appropriate for all beaches and that well-designed and robust monitoring is required to assess the efficacy of any design changes.

This study was made possible by a National Fish and Wildlife Foundation (NFWF) grant (Project No. 9933.12.026318) awarded to Martin County. The following individuals and organizations provided administrative, technical, and analytical assistance during the study: Jeff Tabar, a civil engineer and valued colleague, was largely responsible for the genesis of this study; Kathy Fitzpatrick, Martin County Coastal Engineer, fully embraced the study and was instrumental in securing the NFWF grant; Jessica Garland (Coastal Program Manager) and Michael Cook (Engineer) of the Martin County Public Works Department provided grant administrative assistance and professional guidance on RTK GPS surveying standards, respectively; Dave Holt and Earl Soeder of GPServ provided training and troubleshooting with the RTK GPS instrumentation and assisted in establishing vertical controls; Mike Owen and Bryan Smith of Geomatic Services, Inc., provided verification and quality assurance for GPS data collected throughout the project; David Stites and Mike Trudnak of Taylor Engineering, Inc., provided guidance on engineering aspects of the project; and Drs. Lance Waller, Julie Clennon, and Jenna Krall of the Emory University Department of Biostatistics and Bioinformatics provided GIS spatial analyses and early statistical expertise. Finally, the project would not have been possible without the small army of field biologists and technicians at Ecological Associates, Inc., who conducted the day-to-day monitoring over the course of the project, maintained equipment, and entered and verified data. Drs. Jeanette Wyneken and Michael Salmon graciously provided valuable feedback on an earlier draft of this manuscript, which further benefited from the comments of five anonymous reviewers.