Conservation of the endangered loggerhead turtle (Caretta caretta): Correlations between environmental contaminants, genetic origin, health and hatching success of Western Australian populations.

A project undertaken by Dr Sabrina Trocini at the School of Veterinary and Biomedical Sciences, Murdoch University, and supervised by Prof Ian Robertson, Dr Mandy O’Hara, Prof Stuart Bradley and Dr Kristin Warren.

Worldwide, numbers of loggerhead sea turtles have declined dramatically, and they are now Endangered in Australia and internationally. Western Australia has major foraging and nesting grounds for loggerheads, including large rookeries in Ningaloo and Shark Bay. Despite WA loggerheads being distinct genetic stock from Eastern Australian populations, there have been no long-term data available for WA loggerheads. This multidisciplinary project has undertaken the first study, for WA loggerhead turtles, of genetic origins; environmental toxins; and correlations between these and human impacts, health, and hatching success. Results to date, and those emerging through 2010, will improve our knowledge of WA loggerhead population health, and will be important for sea turtle recovery efforts and WA biodiversity conservation.
This HSF study formed a distinct and key component of a broader study - the first assessment of the health status of WA loggerhead populations. The broader study aims to increase understanding of the factors involved in adult health/disease and hatching success, and to provide data to assess the significance of human-related disturbances, which are stated priorities in Australian sea turtle Recovery Plans. Our aims for this HSF-funded study were:

  1. To measure toxin levels in unhatched eggs, to quantify environmental toxins as risk factors that may reduce hatching success on WA beaches. The broader health/hatching success study is examining other factors in embryo/hatchling death/illness.
  2. To determine types/levels of deformities found in unhatched eggs/ dead hatchlings; and to correlate deformities with toxin levels. The broader study involves correlations between hatchling deformities and maternal clinical health/disease.
  3. To correlate toxicology data with disease prevalence. The broader study will investigate other health risk-factors, particularly in adults.
  4. To determine blood toxin levels in adult nesting females whose nests are sampled. The broader study will assess whether these contaminant levels are associated with abnormal health parameters.
  5. To correlate findings of the toxicological screenings and histopathology with hatching success and nesting female reproductive success.
  6. To determine genetic origins of turtles from which toxicological/health screening samples are collected, and to correlate genetic origin with toxin levels and the broader findings on health/disease/ hatching success.
Results to date

The experimental design incorporated two of WA’s three major loggerhead sea turtle nesting sites: Dirk Hartog Island in Shark Bay, and Bungelup Beach in Ningaloo Marine Park. Field data and biological samples were collected for two nesting seasons (Nov-Mar, 2006/07 and 2007/08).  Collection and analyses of samples are complete, and correlations are well underway between genetic origins, environmental toxins, health and hatching success.  Field work for the last season was affected by three cyclones that impacted heavily on nesting beaches, giving researchers the opportunity to study the impact of storms on hatching success, and findings have been collated as a journal paper (submitted) and thesis chapter (“Biotic and abiotic factors affecting hatching emergence success on Dirk Hartog Island”, final draft).  The cyclones’ impacts on nesting beaches included a large reduction in the number of eggs available for toxicology screening.  With HSF approval, excess funds allocated for toxicology of eggs were redirected to undertake toxicology on dead hatchlings, and other diagnostic tests for health screening of nesting females.  The screening of blood samples has provided reference ranges for several blood health parameters, including haematology, plasma biochemistry, plasma protein electrophoresis, and blood vitamin levels.  Outcomes to date from biochemistry-descriptive analyses and differential white blood cell counts include two papers and thesis chapters in final stages of preparation: (a) “Blood health parameters of nesting loggerhead turtles: reference ranges and comparison with ranges in literature”; and (b) “Does loggerhead turtle health affect reproductive fitness and how are blood health parameters influenced by barnacle load, traumatic injuries, and morphometric patterns?”.  In 2009, results presented at conferences included established reference ranges for haematology, blood chemistry and plasma concentrations of vitamin A, E and D from more than 150 nesting turtles, and comparison of these results with ranges reported in literature.

Highlights from our molecular diagnostics work included the discovery of a new intraerythrocytic protozoal parasite based on light microscopy and morphological ID.  No protozoan haemoparasites have been identified before in sea turtles. The parasite is morphologically similar to a malaria parasite such as Haemoproteus or Plasmodium spp; parasites which are vector-borne and generally transmitted by biting flies of the order Diptera.  Results were presented at 2009 International Sea Turtle Symposium, and a paper has been submitted.  Additional results include the design of a new set of primers to perform quantitative PCR, and genetics findings as noted below.

Results from investigations into deformities include a summary of deformities identified in embryos and hatchlings; and trends continue to be correlated with several nest/ clutch parameters. In particular, results indicating hatching success for individual females have been incorporated into the aforementioned paper “Does loggerhead turtle health affect reproductive fitness and how are blood health parameters influenced by barnacle load, traumatic injuries, and morphometric patterns?” Other results to date include: (a) Completion of sample database of all hatchlings stored in formalin; (b) Establishment of a new histological technique for sexing hatchlings; (c) Identification of skin lesions resembling fibropapillomas in 2 adult turtles, which are being investigated using immunohistochemistry and PCR-based techniques to determine aetiology; (d) Macroscopic categorisation of 658 hatchlings; and (e) Gross necropsy of 262 hatchlings to identify gross lesions.  Toxicology and histopathology results continue to be correlated with other health and hatching success data as part of the broader study, and have been incorporated into the following papers/ thesis chapters: (a) the aforementioned health and reproductive fitness paper/ chapter; (b) “Levels of organic and inorganic pollutants in blood and eggs of nesting Loggerhead turtles” (chapter); and (c) “Levels of heavy metals in blood of loggerhead turtles and influence on health and reproduction”(paper, chapter).

For our genetic sequencing to identify any distinct sub-populations within the WA loggerhead population, we screened samples from Dirk Hartog Island, Shark Bay and Cape Range for eight microsatellite loci. These loci showed very high levels of polymorphism and were suitable to address questions of population differentiation.  Analyses did not indicate genetic differentiation between the three sites.  We also sequenced 74 turtles for 660bp of the mtDNA control region, and found seven haplotypes, of which two were very common among all samples across sites; with no significant differentiation among all samples.  Further analyses suggested that the population has not undergone any genetic bottleneck.  Field observations support our genetic results, as two of the nesting turtles in Cape Range were later caught in Shark Bay.  In addition to these findings, turtles which were positive for specific diseases were matched to genotype, and correlations are continuing between health and genetics as part of the broader study.

Some of this project’s most important conservation outcomes relate to nest predation.  Our work has revealed that predation (by both native and introduced predators, including foxes, ghost crabs and varanid lizards) is a key limiting factor in hatchling success at Cape Range.  Levels of predation measured at Cape Range are considered unsustainable, with 80% of the marked nests showing signs of predation. Our findings suggest a shift in management focus to prioritise research and management on predator dynamics; including the impact of different predators on clutch survival, and effective mitigation strategies.  Key mitigation measures would include further fox control strategies at nesting beaches, and research into whether ghost crab numbers are increased due to anthropogenic factors.  To facilitate conservation decisions, some of these findings have been published in Trocini et al. (2009), a management-focused chapter in the 2009 Ningaloo Research Progress Report (full reference below). Results are also being incorporated into two management papers /thesis chapters: (a) “Nest predation in Cape Range National Park” (submitted), and (b) “High density island nesting beach versus a low density mainland nesting beach: conservation strategies and management options”. 
While HSF funding is now complete, this study is a key part of a broader study as noted above, and correlations are well advanced between genetic and toxicology results, health, and hatching success.  Results and management implications of this research are already proving of interest to conservation agencies, as demonstrated by publication of Trocini et al.'s (2009) chapter in the aforementioned Ningaloo Research Progress Report. We expect this will lead to modification of management protocols for mainland nesting beaches for loggerhead turtles in WA, to prioritize mitigation of current very high levels of predation such as those identified at Cape Range.


Trocini, S., Warren, K., O'Hara, M., Bradley, S. and Robertson, I. (2009) Health and hatching success of Western Australian loggerhead turtle (Caretta caretta) nesting populations, pp22-26 In: Waples, K. and Hollander, E. (eds) Ningaloo Research Progress Report: Discovering Ningaloo  - latest findings and their implications for management.  Ningaloo Research Coordinating Committee.  Department of Environment and Conservation, WA.
Trocini S, Robertson I and Bradley S (2009), Crime scene investigation on a loggerhead turtle nesting beach: Who ate the eggs?  29th Annual Symposium on Sea Turtle Biology and Conservation, International Sea Turtle Society, (presented by Dr Trocini), Brisbane, February 2009.
Trocini S, Spencer P, Bradley S, Warren K, O'Hara A, Perkins S and Robertson I (2009), Health assessment of nesting loggerhead turtles (Caretta caretta) in Western Australia, 29th Annual Symposium on Sea Turtle Biology and Conservation, International Sea Turtle Society, oral presentation (Presented by Dr Trocini), Brisbane, February 2009.
Earlier conference presentations at: (a) Second Annual Ningaloo Symposium, May 2008, (b) Wildlife Disease Association conference, oral presentation September 2008; (c)  International Sea Turtle Symposium January 2008; (d) Wildlife Disease Association 2007

Figure 1. Dr Sabrina Trocini and field assistant recording data. (Photo Dr Sabrina Trocini)

Figure 2. Dr Sabrina Trocini measuring the carapace length of a loggerhead turtle. (Photo Dr Sabrina Trocini)

Figure 3. Sea turtle tracks at Turtle Bay, Dirk Hartog Island. (Photo Dr Sabrina Trocini)


Figure 4. Ghost crab with loggerhead turtle hatchling (Photo D. Mancini)


Figure 5. Perentie excavating turtle nest (Photo Dr Sabrina Trocini)