seaturtle.org : MTN : ARCHIVES : Sign In

To address the matter of egg loss, the Institute of Marine Affairs (IMA) in consultation with GRNTGA developed a novel incubation device for leatherback eggs. The project was conducted in phases: Phase I was an investigation into the feasibility of utilizing wooden containers to incubate leatherback sea turtle egg clutches (Jobity et al. 2014), which gave consideration to the three main factors that must be optimized for sea turtle egg incubation: temperature, moisture and gas exchange (Koch et al. 2007). In Phase I, temperatures within sand-filled wooden containers were recorded and compared to the thermal tolerance range for leatherback embryos (Ackerman 1997), which was estimated at 25-35 °C. The study concluded that the temperature ranges within all three sand-filled wooden containers were 24.7-29.9 °C, 24.3-32.1 °C and 24.7-29.9 °C; all fell within the thermal tolerance range for leatherbacks (Ackerman 1997).

Figure 1. Experimental hatchery enclosure on Grande Riviere Beach.

Phase II of the project involved artificial incubation trials with leatherback egg clutches (Fig. 1) during the 2013 nesting season. Five leatherback clutches that were deemed “high risk of being lost” to natural phenomena (e.g., erosion and/or inundation) were relocated to five sand-filled wooden containers (Jobity et al. 2014). Only five nests were permitted to be relocated because, at the time of the study, leatherback turtles were considered Critically Endangered by the International Conservation Union (IUCN 2014); they are now globally listed as Vulnerable. The objective of this phase was to determine whether the sand-filled wooden containers were capable of incubating leatherback sea turtle eggs. The experimental hatchery housed five wooden containers constructed with pitch pine lathes of dimension 91.4 cm x 61 cm x 91.4 cm and were lined with fine mosquito mesh. Sand was collected from an area above the high tide where leatherbacks usually nest. The sand was hand-sieved with fine wire mesh and wooden handles, and used to fill the wooden containers. Sieving allowed for the removal of all stones and debris (including past seasons’ egg shells) that might impact incubation. An artificial ‘boot-shaped’ nest chamber was excavated inside the sand filled containers down to a depth of 70 cm in keeping with the average depth of a leatherback clutch (Chacon & Machado 2005). The chamber was made only when the eggs were collected for relocation. Once an egg clutch was deemed at “high risk of being lost” to natural phenomena, biometric data of the nesting female were collected she was also checked for flipper tags and for fisheries-related injuries. Her eggs were collected by carefully catching them in plastic bags (with no seam at the bottom of the bag, to prevent the bag from giving way) placed directly below the cloaca. The bag was then closed to prevent heat loss (Chacon & Machado 2005). To avoid contamination, eggs were singly and carefully placed in the artificial egg chamber using gloved hands and in the same order as they were laid; that is, larger fertile eggs followed by the smaller shelled albumin globs/yolkless eggs. The clutch size was simultaneously determined. Approximately halfway through the relocation, HOBO (UA-001-64) temperature loggers were placed with the clutches to automatically record hourly temperature for the duration of the incubation periods. The sand removed to create the chamber was then used to cover over the nest in the wooden container.

Figure 2. Map of Grande Riviere Bay showing the location of the experimental hatchery and natural nests. Map credit: Hamish Asmath - IMA

The five clutches were relocated to the wooden containers within two hours of oviposition, to minimize any movement-induced mortality (Limpus et al. 1979). The wooden containers were covered with mosquito mesh to prevent any infestation by maggots and to hold hatchlings safely in place before subsequent release. The normal incubation period for leatherback turtles is 60 days (Herrera 2006) and the expected date of emergence was calculated with hourly monitoring approximately 2-3 days prior to the expected date of emergence. The incubation period was defined as the time between oviposition and the emergence of the first hatchling.

For comparison to the hatchery nests, five natural nests were selected and data were collected in a similar manner to the artificially incubated nests. Unfortunately, three of the natural nests were lost to erosion so no data were collected on those. Fig. 2 shows the location of the experimental hatchery, the natural nests and the “at risk” nests that were relocated. At the end of the incubation period and after hatchling emergence, hatchling biometric data (curved carapace length, width and weight) were collected and nest excavations were conducted. For excavations, nest contents for both natural and artificially incubated nests were characterized according to (Bell et al. 2006, Hall & Parmenter 2006). The hatching success rate for both natural and artificially incubated nests was calculated using the following formula: Hatching Success Rate (%) = (Total Number of Empty or Hatched shells) / (Total Number of Eggs Incubated) x 100 (Herrera 2006). Unhatched eggs were also staged according to Chacon et al. (2008).

Generally, the project was conducted during the wet season and the average daily temperature for the period (n = 94) was 27.7±4.2 °C (range 24.1 ±0.1 °C to 30.3 ±6.1 °C). The mean temperatures for the two natural nests that were not lost to erosion were 31.1 ±0.2°C and 27.2 ±0.6°C; the hatching success rate was 0%. Average temperatures over the incubation period for artificially incubated nests (n = 5) was 30.2 ±0.8 °C; the mean hatching success rate was 25.1% (range 12.7-31.8; n = 639 eggs). The average worldwide hatching success rate for leatherbacks is 50% (Rafferty et al. 2011). Total hatchling production from the artificial incubation trial was 156 turtles. Fig. 3 outlines the mean ambient temperature inside the hatchery enclosure and the mean temperatures for natural and artificially incubated nests, with respect to the known thermal tolerance range for sea turtle embryos. The average weight of hatchlings that emerged from the trials from was 49.3 g (range 47.3-52.1; n = 15) and the average carapace length was 6.1 cm (range 6.0-6.3; n = 15). According to Rhodin (1985) leatherback hatchlings weigh approximately 30 grams and measure 6 cm in carapace length.

Figure 3. Comparison of ambient conditions at hatchery. Mean temperature in natural nests, Mean temperature in hatchery nests and thermal tolerance range for leatherback incubation (lower and upper limit, from Ackerman 1997).

A suitable gaseous, hydrous (moisture) and thermal (temperature) nest environment is essential for the development of sea turtle embryos (Koch et al. 2007). Throughout the incubation period the temperature for both the natural nests and the five hatchery nests fell within the thermal tolerance range (25-35 °C) for sea turtle embryos (Ackerman 1997).

Our results indicate that the low hatching success rates for both natural and hatchery nests were because of the high percentages of undeveloped and unhatched eggs. Only one natural nest showed high late stage embryonic mortality. In leatherbacks, low hatching success rates may be caused by embryonic mortality, which is poorly understood (Bell et al. 2003). Studies have also shown that undeveloped eggs may possess an embryo that may be invisible to the naked eye. Another factor that may have contributed to the low hatching success rates in both natural and artificially incubated nests was the presence of microorganisms in the nest environment. Sand from areas above the high tide was used to fill the wooden containers and that may have had a high bacterial load. A study conducted by Coutou et al. (2013, unpublished) during the 2011-2012 nesting season found that a host of bacteria existed in leatherback eggshells and in the nest sand on Grande Riviere Beach.

Overall, our results revealed that the containers have the potential to incubate leatherback turtle eggs. However, further studies must be conducted to determine whether an intervention such as artificial egg incubation is required for leatherback sea turtles nesting on Grande Riviere Beach. Recommendations for further studies include: 1) investigation of the overall hatching success rate (%) of leatherback natural beach nests and 2) evaluation of the spatial and temporal distribution of leatherback sea turtle nests and estimation of the extent of egg loss by natural phenomena over the nesting season.

Acknowledgements. The author thanks: The Forestry Division of Trinidad & Tobago for permission to relocate leatherback egg clutches on Grande Riviere Beach, The Green Fund Executing Unit of Trinidad and Tobago (GFEU) for funding this study, Grande Riviere Nature Tour Guide Association for assisting with the project’s activities, Professor Indar Ramnarine, Dr. Ann Marie Jobity, Hamish Asmath, Christopher Alexis, Addison Titus and Kamau Downes.

ACKERMAN, R.A. 1997. The nest environment and embryonic development of sea turtles. In: Lutz, P.E. & J.A. Musick (Eds.). Biology of Sea Turtles. CRC Press, Boca Raton, Florida. pp. 83-103.

BELL, B.A., J.R. SPOTILA, F.V. PALADINO & R.D. REINA. 2003. Low reproductive success of leatherback turtles, Dermochelys coriacea, is due to high embryonic mortality. Biological Conservation 115: 131-138.

CHACON, D. & H.L. MACHADO. 2005. Anidacion de Dermochelys coriacea en Playa Gandoca, Informe Temporada 2005. Projecto de Conservacion de Tortugas Marinas, Talamanca, Caribe Sur, Costa Rica.

CHACON, D., B. DICK, E. HARRISON, L. SARTI & M. SOLANO. 2008. Technical manual of management and conservation of marine sea turtles in Central America. San Jose, Costa Rica. 51pp.

COUTOU, J., S. RAJH, N. STEWART & A. WATSON. 2013. Bacterial flora identified from Leatherback turtle (Dermochelys coriacea) eggshells and nest sand at Grande Riviere beach, Trinidad. The School of Veterinary Medicine, Faculty of Medical Sciences. UWI, Trinidad and Tobago Trinidad and Tobago. 62 pp. Unpublished manuscript.

DUTTON, P.H., S.E. RODEN, K.R. STEWART, E. LA CASELLA, A. FORMIA, J.C. THOME, S.R. LIVINGSTONE, S. ECKERT, D. CHACON-CHAVERRI, P. RIVALAN & P. ALLMAN. 2013. Population stock structure of leatherback turtles (Dermochelys coriacea) in the Atlantic revealed using mtDNA and microsatellite markers. Conservation Genetics 14: 625-636.

ECKERT, S. 2013. An assessment of population size and status of Trinidad’s leatherback sea turtle nesting colonies. WIDECAST Information Doc. No. 2013-01. 14pp.

ECKERT, S.A. 2006. High-use areas for Atlantic leatherback sea turtles (Dermochelys coriacea) as identified using telemetered location and dive information. Marine Biology 149: 1247-1257.

HALL, S.C.B. & C.J. PARMENTER. 2006. Larvae of two signal fly species (Diptera: Platystomatidae), Duomyia foliate McAlphine and Plagiostenopterina enderleini Hendel, are scavengers of sea turtle eggs. Australian Journal of Zoology 54: 245-252.

HERRERA, A.E. 2006. The effects of management methods on sex ratio and hatching success of leatherback turtles (Dermochelys coriacea). Conservation Biology Centre for Ecology and Conservation, UK.27pp.

JOBITY, A.M.C., R. SHOY & J. ALEMU. 2014. Artificial incubation trials of leatherback turtle eggs at Grande Riviere Beach, Trinidad, West Indies. Marine Turtle Newsletter 142:3-6.

KOCH, A.U., M.L. GUINEA & S.D. WHITING. 2007. Effects of sand erosion and current harvest practices on incubation of the flatback sea turtle, Natator depressus. Australian Journal of Zoology 55: 97-105.

LEE LUM, L. 2005. Beach dynamics and nest distribution of the leatherback turtle (Dermochelys coriacea) at Grande Riviere, Trinidad. Revista de Biologiá Tropical 53: 239-248.

LIMPUS, C.J., V. BAKER & J.D. MILLER. 1997. Movement induced mortality of loggerhead eggs. Herpetologica 35: 335-338.

LIVINGSTONE, S.R. 2006. Sea Turtle Ecology & Conservation on the North Coast of Trinidad, West Indies. PhD Thesis, Division of Environmental & Evolutionary Biology. University of Glasgow. 284pp.

RAFFERTY, A.R., P. SANTIDRIÁN-TOMILLO, J.R. SPOTILA, F.V. PALADINO & R.D. REINA. 2011. Embryonic death is linked to maternal identity in the leatherback turtle (Dermochelys coriacea). PLoS ONE 6 (6): e21038. doi: 10.1371/journal.pone.0021038.

RHODIN, A.G. 1985. Comparative chondro-osseous development and growth of marine turtles. Copeia 1985: 750-771.