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Health assessment and hatching success of two Western Australian loggerhead turtle (Caretta caretta) populations

Trocini, Sabrina (2013) Health assessment and hatching success of two Western Australian loggerhead turtle (Caretta caretta) populations. PhD thesis, Murdoch University.

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Most of the existing sea turtle populations worldwide are in decline, and loggerhead turtles (Caretta caretta), in particular, are listed as Endangered. The loggerhead nesting population in Western Australia is the largest nesting population in Australia and one of the largest in the Indian Ocean and the world.

This research project investigated hatching success and health, two critical aspects for loggerhead turtle conservation and management, on two important nesting sites in Western Australia: Turtle Bay on Dirk Hartog Island and Bungelup Beach in Cape Range National Park. This project undertook an inter-disciplinary approach encompassing the disciplines of conservation medicine, ecology and epidemiology to investigate questions about sea turtle conservation that could not be addressed by any of these disciplines alone.

Morphological and reproductive measurements were collected during two nesting seasons, between 2006 and 2008, obtaining important baseline reproductive data about the Western Australian population. It was found that the presence of deformed and yolkless eggs was associated with smaller clutch size. At the same time several biotic and abiotic factors were assessed in relation to embryonic and hatchling mortality. Hatching success was significantly reduced by high temperatures during the pre-emergent period, the presence of roots in the nest and nest location along the beach. Results suggest that bacterial contamination of sand on the high nesting density beach sectors may, in part, be responsible for the differences in hatching success along the beach. High nest temperature during the pre-emergent period also significantly reduced emergence success and influenced emergence patterns and duration. Prolonged emergence duration, associated with increased nest temperatures, may further reduce hatchling survival due to diminished energy reserves and increased risk of predation.

On the mainland nesting site, Bungelup Beach, predation of eggs and hatchlings severely limited reproductive success with over 80% of the monitored nests showing signs of partial or complete predation. In contrast with that reported in the literature, ghost crabs (Ocypode spp) were the main predator at this site and the first among the identified predators to dig into nests. Perentie (Varanus giganteus) and introduced foxes (Vulpes vulpes) also predated on eggs and hatchlings, making the level of predation recorded unlikely to be sustainable in the long term.

Health monitoring of the nesting populations enabled the determination of baseline blood health parameters and toxin levels in blood. Two cases of fibropapillomatosis were confirmed for the first time in Western Australian loggerhead turtles. Changes in the leukogram and some biochemical parameters were detected in association with the presence of barnacles, in particular burrowing barnacles. In order to establish the connection between the nesting turtles’ health and reproductive success, maternal health indices were compared to hatching success and reproductive output. Several blood health parameters, including alpha and gamma proteins, iron, zinc and vitamin E levels, were correlated with hatching success or clutch size, suggesting that these parameters influence reproduction in loggerhead turtles. Additionally, sea turtles with reproductive abnormalities, such as soft-shelled or deformed eggs, had higher blood mercury levels than turtles without any egg or clutch abnormalities. This finding raises important questions about the toxic effect of mercury, at low blood concentrations, on sea turtle reproduction.

During the health assessment, a novel intraerythrocytic protozoal parasite species, similar to a malaria parasite (Haemoproteus and Plasmodium spp), was identified for the first time in sea turtles and was described through the use of light microscopy and diagnostic molecular techniques. The phylogenetic analysis indicated that this new parasite is closely related to other haemosporidia isolated from chelonians, but is well separated from malaria parasites isolated from other hosts (e.g. mammals, birds and other reptiles). This parasite appears to be largely benign. Although parasitaemia was low in all infected individuals, further studies are required to assess the potential impact of this haemoparasite on sea turtle fitness.

In conclusion, this study provided further understanding of factors affecting reproductive success, identified threats to the Western Australian nesting population whilst at the same time enabling assessment of the general health of nesting loggerhead turtles in Western Australia.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Robertson, Ian, O'Hara, Amanda, Warren, Kristin and Bradley, Stuart
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