Leatherback Sea Turtle Nest Monitoring

Sampling methods were approved by St. George’s University Institutional Animal Care and Use Committee (IACUC-16017-R); permits were acquired from the Fisheries Division of the Grenada Government Ministry of Agriculture, Lands, Forestry, Fisheries, and the Environment.
Data for this study were collected from Levera Beach (12°13′75″ N, 61°36′78″ W) in Grenada, from the 2015 to 2019 nesting seasons from March through August (Figure 1). The beach is within a Ramsar Protected Area and is closed to public use during the leatherback nesting season. Data collection methods are those used with nest monitoring strategies employed by Ocean Spirits Inc. [4 ]. Nightly beach patrols were conducted every 30 min between 19:30 and 06:00 to detect nesting female leatherback sea turtles. Biometric data, including curved carapace length (CCL) and curved carapace width (CCW), and details from Monel (National Band and Tag Company, Kentucky, USA) and Passive Integrated Transponder (PIT) tags (Biomark, Idaho, USA) were collected to associate individual turtles with nesting data.
The 750 metre white, fine sand beach was divided into four 187 metre wide zones (zone 1–4) and subdivided with wooden markers placed 30 m apart (Zones A-Z) to allow nests to be found for excavation (Figure 1). Nest distances from the seaward edge of vegetation and high-water marks were recorded. Doomed nests laid within known washout/erosion areas, below the high-water mark, or sited too close to vegetation, were relocated to an area on the beach where the nest would be at a lower risk [4 ]. Nest relocations were dug by hand and measured using a soft tape to ensure they were of similar depth and width to a natural nest, to ensure incubation was not impacted by the relocation. Nest relocation likely influenced environmental data and overall hatchling success recorded in this project but priority was given to efforts to support conservation efforts.
From May to September of each nesting season, 10% of the total confirmed in situ and relocated nests laid at Levera Beach were selected at random and excavated, either two days post-hatchling emergence or 70 days post-ovipositioning if emergence was not observed. This delay in excavation was to provide adequate time for complete emergence of any viable hatchlings. Nest locations were excavated to a depth of one metre deep and a width of one metre wide by hand (latex gloves were worn), the excavator determining lower sand desnity by touch. Depth to the top and bottom of the egg chamber, was determined using a soft 1 m tape.
Excavated contents were catergorised based on WIDECAST (Wider Caribbean Sea Turtle Conservation Network) protcols as being: (1) empty shells, signifying hatched eggs; (2) unhatched eggs containing embryos measuring <5 mm in length to full term; (3) yolked eggs with no gross signs of development; and (4) unfertilized shelled albumin masses (Figure 2). Embryonic development success rate was calculated as the sum of the number of hatched eggs and eggs with embryos divided by the number of laid eggs (excluding shelled albumin masses), with the embryonic development success rate representing laid eggs that had the potential to develop into hatchlings. Hatchling success rate was calculated as the number of hatched eggs divided by the number of laid eggs (excluding shelled albumin masses) [25 ]. This represented the percentage of eggs that hatched. Unhatched eggs were examined for the presence of visible external or internal pink to purple discolouration, interpreted to be bacterial or fungal growth, and/or inspissation of yolk which imparted a coagulated appearance to the internal contents (Figure 2).