A Necropsy-based Study of Green Turtles (Chelonia mydas) in South-East Queensland

Gordon, Anita Nancy (2005). A Necropsy-based Study of Green Turtles (Chelonia mydas) in South-East Queensland PhD Thesis, School of Veterinary Science, University of Queensland.

       
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Author Gordon, Anita Nancy
Thesis Title A Necropsy-based Study of Green Turtles (Chelonia mydas) in South-East Queensland
School, Centre or Institute School of Veterinary Science
Institution University of Queensland
Publication date 2005
Thesis type PhD Thesis
Supervisor Roger Kelly
Abstract/Summary Causes of morbidity and mortality were investigated for 108 green turtles (Chelonia mydas) stranded in south-east Queensland between 1990 and 1996. This study was undertaken as part of a broader carcass salvage program for south Queensland, and within the context of a population study of C. mydas in the Moreton Bay feeding ground. Accurate pathological characterisation of disease in C. mydas was achieved by detailed necropsy and histological examination. Varied inflammatory responses and degenerative changes were observed in stranded C. mydas. Supportive disciplines of microbiology, parasitology, and clinical chemistry were used to elucidate aetiology and pathogenesis of selected conditions. Heavy metal and pesticide levels were assessed in a sub-sample of turtles. Direct anthropogenic causes (including trauma, foreign body ingestion and drowning) accounted for 34% of mortalities of C. mydas in this study. The majority of the trauma cases were turtles with skull fractures resulting from blunt impacts. The remainder had boat propeller injuries, or miscellaneous trauma. Almost half of the turtles with lethal boat propeller damage had evidence of pre-existing disease which may well have predisposed them to boat strike, emphasising the importance of full necropsy examination, even when the cause of death appears obvious. Fishing line was the only ingested foreign body consistently implicated in the production of fatal intestinal obstruction. Marine turtle fibropapillomatosis, a panzootic viral disease which is considered to involve some indirect anthropogenic factors, accounted for 7% of mortalities. The findings in this study were consistent with much of the previously described pathology of this condition. Naturally-occurring diseases (for which human influences are unknown) accounted for the remaining 59% of strandings. Coccidiosis, caused by Caryospora cheloniae, was recorded for the first time in wild C. mydas. It occurred both as an epizootic (in 1991) and as sporadic cases. A variety of manifestations, including disseminated and enteric forms, were recognised. Infection with a Cryptosporidium-like protozoan appeared to occur concurrently with coccidiosis in one turtle in this study. Attempts to establish experimental coccidial infections in hatchling C. mydas were unsuccessful. Infections with cardiovascular (spirorchid) flukes were almost universal in stranded C. mydas in this study. They ranged from mild, incidental findings (such as occasional fluke egg granulomas evident microscopically in otherwise normal tissues) to a variety of severe changes, including thrombosis, which were likely to have produced morbidity. The present study clarified the range of cardiovascular lesions associated with spirorchidiasis, including the sequence of thrombus resolution and exteriorisation from vessels. In some cases spirorchid vasculitis was associated with fatal disseminated bacterial infections. Other sporadic, naturally-occurring diseases included mycotic pneumonia, bacterial meningoencephalitis and a miscellany of gastrointestinal conditions, including chronic intestinal tympany and obstipation, for which the underlying cause could not always be determined. Evidence indicated that gastrointestinal motility in C. mydas was prone to both direct and indirect disturbance and that tympany and obstipation could be final common outcomes of a range of insults. Eighteen abnormally buoyant turtles were examined during this study. The cause could usually be ascribed to an underlying disease, including (in decreasing order of frequency) trapped internal gas, usually intestinal; neurological disease such as traumatic brain injuries; and pulmonary disease. In two cases, no underlying cause was detected. Trace metal (arsenic, cadmium, mercury, selenium and zinc) concentrations were determined in the livers and kidneys of 50 turtles of mixed species (mostly C. mydas). These results were considered to provide baseline data for sea turtles in SE Qld. This study offered the largest dataset available for some metals in C. mydas, and provided evidence of high background levels of cadmium as a normal feature for the species. Some unusual age–related trends in metal accumulation were detected. Concentrations of cadmium, zinc and selenium in the kidney decreased with increasing age, whereas zinc concentrations in the liver tended to increase. Determining the impact of disease on wildlife populations is an increasingly necessary task, which will require multidisciplinary teams. Necropsy surveys like the present study are an essential component of the growing field of conservation medicine. In addition to providing data relevant to management, such as the relative proportions of anthropogenic and naturally-occurring mortalities, necropsy surveys can identify a range of endemic pathogens, and help to collect prevalence data for determining disease impacts at the population level.

 
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Created: Fri, 21 Nov 2008, 16:23:14 EST