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Figure 1. Development behind Levera Beach, with removal of buffer vegetation and exposure of fine sediments that wash over the beach in August 2002 (top) and again in August 2003 (bottom).

In 2004, an 18 hole golf course was completed as a first step in the development of a resort adjacent to Levera (Figure 1). Removal of near shore vegetation and lack of proper run-off prevention from the construction by the developer resulted in the deposition of fine sediments and mud over approximately 15% of the nesting beach. To evaluate the effects of this sedimentation on nesting activities, we documented the locations of nesting events over a 9 week period (May-June) of the 2005 nesting season and compared nest distribution to the distribution of nests from 2001- 2004.

For the 2005 nesting season, Levera Beach was divided into 24 zones (each 30m long). The locations of zones, marked by wooden stakes at the vegetation line, were similar to zones established previously by the Ocean Spirits, Inc. research project. Each stake’s location was documented with a handheld GPS. Beach profiles were recorded weekly originating from every other stake following methods described by Fish et al. (2005). During nightly beach patrols, the zone was recorded for observed nests and, where possible, nests were triangulated from the two nearest stakes by using a meter tape to determine the distance from each stake to the center of the nest. Using a combination of MapInfo™ and ArcGIS™ software, beach marker positions and waterline profiles were converted to latitude/longitude coordinates and plotted on a map. Historical nest distribution data from 2001-2004 were also acquired and used in this analysis. Nest locations for 2001-2004 seasons were reported according to the zone within which each nest occurred.

Figure 2. Distribution of turtle nests along Levera Beach in the 2005 nesting season.

There were 237 nests laid between 30 April and 28 June 2005; of these, we recorded zones for 219 nests. Most nesting occurred within zones B-C and T-X (Figure 2). There was a strong tendency in 2005 for nests to be laid along the northern side of the beach when compared to the east facing side of the beach. The percentage of total nests laid on the north facing side of the beach increased over the course of the nesting season with 39.6% in week 1 increasing to 64.3% of nests laid in week 8 located on the north facing side (Figure 3).

Figure 3. Over time, increasingly more nests are laid on the North side (diamonds) and in the affected area (zones U-X, squares).

Historical data gathered between 2001 and 2004 showed a similar pattern of nesting along the north and east sides of Levera Beach (Table 1). The percent of nests laid on the north coast varied from 47% - 82% between 2001 and 2004.

Table 1. Distribution of turtle nests on North Side and Zones U-X along Levera Beach from 2001-2005.

Figure 4. Beach profiles from north-facing (upper panel) and east-facing (lower panel) zones of Levera Beach show net erosion trends.

Erosion patterns varied by beach section in 2005, with the east facing beach eroding an average of 8.77 meters and the northern side of the beach expanding an average of 9.32 meters over the course of this study (Figure 4). Deposition of fine sediments from the construction project was highest between zones U through X (Figure 5).

Figure 5. Map showing beach markers and the full range of beach width observed over the course of the study period.

Our results suggest that turtles responded to the accretion of the north facing beach and erosion of the east facing beach in 2005 by nesting more often on the north facing beach. Changes in nesting density of leatherbacks as related to erosion/accretion patterns have been reported in French Guiana (e.g. Kelle et al. 2007) and Trinidad (Lee-Lum 2005). Erosion of the east facing beach over the season may have created a steeper approach slope; at times a steep berm was created at the shoreline. Accretion of the north facing side would presumably create a more gradual approach, gentler slope, and easier access for sea turtles (Sivasundar 1996; but see Hendrickson & Balsingham 1966, Mortimer 1982). The near shore environment at Levera is characterized by strong currents, which influence not only erosion and accretion patterns of the beach, but possibly turtle nesting behavior. For instance, multiple turtles emerging at the same time and place after long periods of inactivity in one evening has been observed at Levera, and may be explained in part by these currents or some other temporal or social variable not being considered.

While some studies suggest that offshore configurations and approaches are important for selection of nesting beaches by female turtles (Mortimer, 1982; Pritchard, 1971), selection of the nesting location on the beach remains poorly understood (e.g. Miller et al. 2003). Although leatherbacks tend to nest in open sand areas free of obstruction, above the high tide line but below the vegetation (Kamel & Mrosovsky, 2003; Nordmoe, et al., 2003), it has been suggested that individual leatherback turtles nest in a random pattern in order to maximize nest survival in unpredictable environments (Mrosovsky 1983; Eckert, 1987). From a management perspective, the first step is to document where turtles choose to deposit nests and perhaps address the question of ‘why’ as a secondary concern. Locations with higher nesting density indicate particular portions of beach that should be protected from severe alteration, especially because it is unclear what factors contribute to the selection of these particular sites.

In the case of Levera Beach, each season, nearly 20% of all nests laid occurred in the area (Zones U-X) that has been affected by development (Table 1). These zones are subjected to ongoing run-off that has resulted in deposition of finer material where turtle nests are laid. Karavas et al. (2005) reported that an increase in finer-grained sand is proportional to the reduction of loggerhead nesting activity, possibly because turtles prefer coarser-grained sand for their incubating eggs. Hendrickson & Balsingham (1966) suggested that species-specific preferences in sand grain size in Malayan sea turtles result in the separation of nesting beaches of greens (finer sand) and leatherbacks (coarser sand). Mortimer (1982) and Pritchard (1971) both pointed out, however, that in Malaya, sand grain size is correlated with the steepness of slope of the beach. Mortimer (1982) also noted that nests can fail in substrates that are either too fine or too coarse, but overall particle size is less important in nest site selection by females than offshore configuration. Leatherback females nesting at Levera Beach do not appear to be impacted by the change in sand grain size in Zones U-X, because comparable proportions of turtles nested in the affected area before and after changes occurred in sand composition and grain size.

The sediment deposited by runoff in Zones U-X may reduce hatch success of nests laid there by restricting gas exchange between developing eggs and finer sand (Prange & Ackerman 1974). For instance, leatherback eggs in Australia had high levels of early embryonic mortality when fine sand in and around the nest became wet and reduced gas exchange (Limpus et al. 1984). Also, loggerhead clutches laid in clay material on the beach in Cape Verde had reduced hatch success, presumably due to impeded gas exchange (Marco et al. 2008). Another impact of the runoff is that deposited material is darker in color than the naturally occurring sand, which in turn tends to cause temperatures at nest depth to be warmer through increased absorption of solar radiation (Hays et al. 2002). Increased sand temperatures may affect sex ratios of hatchlings and/or reduce hatch success (Matsuzawa et al. 2002). Additionally, material deposited by runoff may be more compacted than natural sand, which may impact hatchlings as they emerge from the nest (Crain et al. 1994). Finally, the runoff itself can occur during the nesting season, effectively burying incubating nests deeper under the deposited material, and likely reducing hatching success.

The current management strategy on Levera beach incorporates actions that are intended to maximize the reproductive success of Levera’s nesting leatherback population. This includes manual relocation of individual nests laid in unsuitable areas. In 2005, 20 out of 42 nests laid in the affected area were relocated to more suitable sites, due to projected impacts from the runoff. Without these relocations, up to 10% of the total nests laid during the study period may have been lost due to impacts of runoff from the development site. Continued implementation of this management tool is recommended as long as the north side of the beach continues to suffer from unfavorable altered sand composition. In addition, future monitoring should evaluate the success of these relocation efforts.

Continued monitoring of the impacts of coastal development on leatherback reproductive success is needed at Levera Beach. For example, the removal of coastal vegetation is likely to leave the north-facing side of Levera unprotected from higher seas encountered outside the nesting season and thus more vulnerable to erosion, and increased human traffic and artificial lighting on the beach associated with hotels may negatively impact nesting females and hatchlings. More information on these impacts should help inform future management actions on Levera Beach.

Acknowledgements: We thank the following: Ocean Spirits, Inc. for providing historical data, photographs, and additional guidance; the Summer 2005 Ocean Spirits volunteers Sleepy, Sneezy, Sweety, Stinky, and Smoky for their help in data collection and unrivaled company; Dr. Karen Eckert for her advice and guidance; Venance Msacky, Grenada Lands and Surveys Division for assistance collecting GPS data; Division of Fisheries, Ministry of Agriculture, Forestry and Fisheries, in particular Crafton Isaacs and Paul Phillips, Fisheries Officers; and the reviewers for their comments and suggestions that improved this manuscript. Project funding was provided by: Student International Discussion Group, The Kuzmier-Nikitine-Lee Fund, The Whitney Chamberlin Fund, and a Columbus Zoo Grant through WIDECAST.

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