Environmental and Nesting Variables Associated with Atlantic Leatherback Sea Turtle (Dermochelys coriacea) Embryonic and Hatching Success Rates in Grenada, West Indies

Abstract

Annual monitoring of leatherback sea turtle (Dermochelys coriacea) nesting grounds in Grenada, West Indies has identified relatively low hatch rates compared to worldwide trends. This study investigated the impact of selected environmental variables on leatherback sea turtle embryonic development and hatching success rates on Levera Beach in Grenada between 2015-2019. The mean number of nests per year and eggs per nest were 667.6 ± 361.6 and 80.7 ± 23.0 sd, respectively. Within excavated nests, 35.6% ± 22.0 sd of eggs successfully developed embryos and 30.6% ± 22.6 sd of eggs successfully hatched. The number of eggs per nest, along with embryo and hatching success rates, differed by nesting year. Embryo development success rate was associated with nest location, and both embryo development and hatching success rates were positively associated with nest depth and negatively associated with the percentage of eggs exhibiting microbial growth and with the presence of inspissated yolk. There was no embryo development or hatchling success association with month of the nesting season, distance from the high-water mark, distance from vegetation, nor maternal carapace length. The mean nest temperature was 31.7 °C ± 1.64 sd and mean temperatures during the middle third of egg incubation suggest clutches are highly skewed towards a preponderance of female hatchlings. Histopathologic findings in hatchling mortalities included severe, acute, multifocal, heterophilic bronchopneumonia with intralesional bacteria in 4/50 (8%) hatchlings. Data from this study guide conservation strategies by identifying risk factors and further avenues of research needed to support reproductive success of leatherback sea turtles in Grenada and the greater Caribbean region.

Keywords: hatchling; leatherback sea turtle; nesting; reproductive success.

Figure 1

Geographic location of leatherback sea turtles (Dermochelys coriacea) nesting grounds on Levera Beach, Grenada (red square) and schematic of 187 m zones 1–4 and 30 m subzones A-Z used to mark and relocate nests at excavation. (Photo courtesy of Nicolas Winkler).

Figure 2

Leatherback sea turtle (Dermochelys coriacea) egg development stages used to characterize embryonic development success and selected observed gross changes. (a) No gross signs of development and variously staged embryo development at (b) <5 mm, (c) 5 mm–2 cm, and (d) >2 cm in size and (e) full term. Embryos were examined for pathologic changes consisting of yolk discolouration (f) and/or (g) yolk inspissation, (photo credit KEC).

Figure 3

Time-series plot of nest temperatures recorded by temperature loggers deployed in leatherback sea turtle (Dermochelys coriacea) nests in March (Nest 1–3), April (Nest 4–5), May (Nest 6–7) in 2019 on Levera Beach, Grenada.

Figure 4

Histopathologic findings in leatherback sea turtle (Dermochelys coriacea) post-hatching mortalities. (a) Large focus of heterophilic debris and necrosis within the airway of a bronchi (circled). (b) Multiple areas of cellular and heterophilic debris within falveolar spaces (arrows). (c) Cellular and acellular debris within faveolar spaces is associated bacteria lining the bronchi epithelium (arrowheads). (d) Disruption of the sarcolemma of two skeletal muscle bundles by mineral deposits.